Irish Weather Online: Nabro Volcano Stops Erupting After 16 Days
Satellite imagery has confirmed that the Nabro volcano in north east Africa is no longer emitting ash, sulphur dioxide or water vapour.
The Eritrean stratovolcano has been spewing ash continuously since it erupted for the time in its recorded history on June 12 last. During the 16-day period much of northern Ethiopia and parts of neighbouring Djibouti and Sudan have been affected by the ash cloud, which also disrupted air traffic in the region.
The below image from Modis, captured at 11am (GMT) on Thursday reveals that eruption activity at the volcano has ceased. This is also confirmed by the Toulouse-based Volcanic Ash Advisory Centre (VAAC).
Nabro began erupting on Sunday 12 June, 2011, the first ever recorded eruption of the stratovolcano. The resultant ash plume, extending up to 15km into the air, led to some flight cancellations in neighbouring Sudan, Djibouti and Ethiopia. The ash cloud was carried as far away as Saudi Arabia, Israel, Turkmenistan, Somalia, the Central African Republic (CAR) and Egypt. A second eruption on Thursday 16th June sent a massive ash plume westnorthwest over Sudan. The volcano had continued to emit varying amounts of ash, SO2 and water vapour since.
Part of the Afar Triangle, Nabro is one of many volcanic caldera complexes in the north easternmost part of the East African Rift valley region. The stratovolcano is located in the Danakil Depression, close to Eritrea’s border with Ethiopia and north of Djibouti, and has not erupted in at least 150 years. According to data, a similar volcanic eruption in Eritrea occurred in 1861, in Dubbi, Southern Denkel.
Nabro is the most prominent of 3 large volcanoes (Nabro, Dubbi, Mallahle) in the region, each containing a large summit caldera. Nabro comprises lava domes, lava flows, and two calderas, 8 and 5 km in diameter.
The volcano is located along the Great Rift Valley, also known as the East African Rift. the divergent plate boundary extends from the Afar Triple Junction southward across eastern Africa, and is in the process of splitting the African Plate into two new separate plates, the Nubian Plate and the Somali Plate. Seismic activity is frequent in Ethiopia In 1961 alone three thousand tremors were recorded from the centre of the Wollo province resulting in a 20km fissure being opened on the slopes of the Borkena graben.
Thursday, June 30, 2011
World Travel Watch: Puyehue Volcano Could Blow Again;
Hartford Courant: World Travel Watch: Puyehue Volcano Could Blow Again
Chile: Chile's National Service of Geology and Mining has warned that another eruption at the Puyehue volcano is possible after a cork of lava emerged, blocking more lava from spewing out of the mountain. The cork means that a build-up of pressure can occur, possibly leading to another massive explosion. Minor tremors continue to be measured around the volcano, increasing the potential for another eruption. Puyehue is the site of the June 4 blast that caused hundreds of flight delays and cancellations.
Chile: Chile's National Service of Geology and Mining has warned that another eruption at the Puyehue volcano is possible after a cork of lava emerged, blocking more lava from spewing out of the mountain. The cork means that a build-up of pressure can occur, possibly leading to another massive explosion. Minor tremors continue to be measured around the volcano, increasing the potential for another eruption. Puyehue is the site of the June 4 blast that caused hundreds of flight delays and cancellations.
Monday, June 27, 2011
Humans Dwarf Volcanoes for CO2 Emissions
Discover News: [The headline is reversed, and I fixed it in the title to this blog, but leave it the way it appears on the website here]: Volcanoes Dwarf Humans for CO2 Emissions
Colossal, mind-bogglingly hot and capable of spewing billowing clouds of flight-grounding smoke and searing, molten lava, volcanoes are spectacular displays of the massive forces at work inside our planet. Yet they are dwarfed by humans in at least one respect: their carbon dioxide emissions.
Despite statements made by climate change deniers, volcanoes release a tiny fraction of the amount of carbon dioxide emitted by human activities every year.
In fact, humans release roughly 135 times more carbon dioxide annually than volcanoes do, on average, according a new analysis. Put another way, humans emit in under three days the amount that volcanoes typically release in a year, according to the best estimates of volcanic emissions.
"The question of whether or not volcanoes emit more CO2 than human activity is one I get more than any question in my email from the general public.' said Terrence Gerlach, a retired volcanologist, formerly with the Cascades Volcano Observatory, part of the US Geological Survey in Vancouver, Wash. Even earth scientists who work in other areas often pose him the question, he said.
To lay out a clear answer, Gerlach compiled the available estimates of CO2 emissions from all global volcanic activity on land and undersea and compared them with estimates for human emissions. He published the compilation in Eos, a publication of the American Geophysical Union.
Researchers estimate the amounts of carbon dioxide released by terrestrial volcanic eruptions by methods including remote sensing or flying through clouds of erupting volcanic gas, and by measuring certain isotope concentrations near undersea volcanoes. Carbon dioxide is dissolved in magma at great depths and is released as the magma rises to the surface.
"A lot of climate skeptics claim that volcanoes emit more CO2 than humans do," Gerlach said. "They never give any numbers, but the fact is you will never be able to find the volcanic gas scientist that will agree to that," he said.
One example of these skeptic's claims is the 2009 book, "Heaven and Earth: Global Warming, the Missing Science" by Ian Plimer of the University of Adelaide, who did not respond to Discovery News' requests for comment.
"The main reason, I think, that this myth persists," Gerlach said: "First of all, the emissions are extremely spectacular. When people see volcanic eruptions on television and it's awesome, and it's very easy for people to imagine that huge amounts of CO2 are being emitted to the atmosphere."
"However, these spectacular volcanic explosions that are so stunning on TV last only a few hours," he added. [Actually that is incorrect. Some volcanoes spew gases for weeks.[ "They are ephemeral. In contrast, the sources of anthropogenic CO2 (smokestacks, exhaust pipes, etc) are comparatively unspectacular, commonplace, and familiar, and in addition they are ubiquitous, ceaseless, and relentless. They emit CO2 24/7."
While there is uncertainty in the measurements--researchers estimate between 0.13 and 0.44 billion metric tons per year, with their best estimates between 0.15 and 0.26 billion tons--even the highest end of the range is dwarfed by anthropogenic emissions of 35 billion metric tons in 2010.
Gerlach noted that human land-use changes alone, which include deforestation, release 3.5 billion metric tons per year. Cars and light-duty trucks produce 2 billion metric tons; even cement production produces 1.5 billion tons. Any of these by itself is still several times higher than the annual emissions of all of the world's volcanoes .
Pakistan or Kazakhstan each produce about the amount of CO2 as volcanoes do each year, Gerlach noted in the article.
In yet another comparison, Gerlach reported that in order for volcanic emissions to match those made by humans, the May 18, 1980, Mount St. Helens eruption would need to happen every 2.5 hours. The June 15, 1991, Mount Pinatubo eruption would need to occur every 12.5 hours.
"There is no way you can escape the fact that volcanoes are releasing a tiny amount of emissions right now," said Bernard Marty of the Centre de Recherches Petrographiques et Geochimiques in Nancy, France. "There is no doubt about this."
"Even if you do the reverse and you compute how much volcanism should happen to match atmospheric levels, you end up with completely unrealistic eruption rates," he said.
Marie Edmonds, a volcanologist at Cambridge University agreed. While volcanoes are the most important natural source of atmospheric CO2, she noted, "The results show clearly that the amount is 100-150 times less than anthropogenic amounts."
Colossal, mind-bogglingly hot and capable of spewing billowing clouds of flight-grounding smoke and searing, molten lava, volcanoes are spectacular displays of the massive forces at work inside our planet. Yet they are dwarfed by humans in at least one respect: their carbon dioxide emissions.
Despite statements made by climate change deniers, volcanoes release a tiny fraction of the amount of carbon dioxide emitted by human activities every year.
In fact, humans release roughly 135 times more carbon dioxide annually than volcanoes do, on average, according a new analysis. Put another way, humans emit in under three days the amount that volcanoes typically release in a year, according to the best estimates of volcanic emissions.
"The question of whether or not volcanoes emit more CO2 than human activity is one I get more than any question in my email from the general public.' said Terrence Gerlach, a retired volcanologist, formerly with the Cascades Volcano Observatory, part of the US Geological Survey in Vancouver, Wash. Even earth scientists who work in other areas often pose him the question, he said.
To lay out a clear answer, Gerlach compiled the available estimates of CO2 emissions from all global volcanic activity on land and undersea and compared them with estimates for human emissions. He published the compilation in Eos, a publication of the American Geophysical Union.
Researchers estimate the amounts of carbon dioxide released by terrestrial volcanic eruptions by methods including remote sensing or flying through clouds of erupting volcanic gas, and by measuring certain isotope concentrations near undersea volcanoes. Carbon dioxide is dissolved in magma at great depths and is released as the magma rises to the surface.
"A lot of climate skeptics claim that volcanoes emit more CO2 than humans do," Gerlach said. "They never give any numbers, but the fact is you will never be able to find the volcanic gas scientist that will agree to that," he said.
One example of these skeptic's claims is the 2009 book, "Heaven and Earth: Global Warming, the Missing Science" by Ian Plimer of the University of Adelaide, who did not respond to Discovery News' requests for comment.
"The main reason, I think, that this myth persists," Gerlach said: "First of all, the emissions are extremely spectacular. When people see volcanic eruptions on television and it's awesome, and it's very easy for people to imagine that huge amounts of CO2 are being emitted to the atmosphere."
"However, these spectacular volcanic explosions that are so stunning on TV last only a few hours," he added. [Actually that is incorrect. Some volcanoes spew gases for weeks.[ "They are ephemeral. In contrast, the sources of anthropogenic CO2 (smokestacks, exhaust pipes, etc) are comparatively unspectacular, commonplace, and familiar, and in addition they are ubiquitous, ceaseless, and relentless. They emit CO2 24/7."
While there is uncertainty in the measurements--researchers estimate between 0.13 and 0.44 billion metric tons per year, with their best estimates between 0.15 and 0.26 billion tons--even the highest end of the range is dwarfed by anthropogenic emissions of 35 billion metric tons in 2010.
Gerlach noted that human land-use changes alone, which include deforestation, release 3.5 billion metric tons per year. Cars and light-duty trucks produce 2 billion metric tons; even cement production produces 1.5 billion tons. Any of these by itself is still several times higher than the annual emissions of all of the world's volcanoes .
Pakistan or Kazakhstan each produce about the amount of CO2 as volcanoes do each year, Gerlach noted in the article.
In yet another comparison, Gerlach reported that in order for volcanic emissions to match those made by humans, the May 18, 1980, Mount St. Helens eruption would need to happen every 2.5 hours. The June 15, 1991, Mount Pinatubo eruption would need to occur every 12.5 hours.
"There is no way you can escape the fact that volcanoes are releasing a tiny amount of emissions right now," said Bernard Marty of the Centre de Recherches Petrographiques et Geochimiques in Nancy, France. "There is no doubt about this."
"Even if you do the reverse and you compute how much volcanism should happen to match atmospheric levels, you end up with completely unrealistic eruption rates," he said.
Marie Edmonds, a volcanologist at Cambridge University agreed. While volcanoes are the most important natural source of atmospheric CO2, she noted, "The results show clearly that the amount is 100-150 times less than anthropogenic amounts."
Nabro Volcano Eruption In Eritrea Rumbles Into Third Week
IrishWeatheronline: Nabro Volcano Eruption In Eritrea Rumbles Into Third Week
A volcano that erupted for the first time in recorded history more than two weeks ago is continuing to emit large volumes of ash and sulphur dioxide (SO2) into the skies over Eritrea and northern Ethiopia.
The Nabro stratovolcano, which is located close to Eritrea’s border with Ethiopia in northeast Africa, temporarily affected air traffic two weeks ago when the ash plume drifted as far away as Israel, Jordan, Turmenistan and the Central African Republic (CAR).
Images from the MODIS satellite showed a thick ash plume drifting over Eritrea’s border into Ethiopia Monday afternoon. The volcanic ash was drifting SSW. Winds in the region were light NNE when the below images were captured at midday Monday.
Meanwhile, the eruption of the stratovolcano has created a new landmass, according to the director general of Mines at the Ministry of Energy and Mines, Mr. Alem Kibreab. Mr. Alem said that the ash and lava emitted from the Southern Red Sea region volcano has created a new land mass measuring hundreds of square metres. The director general also disclosed that a team composed of geological and volcanic experts is conducting studies in the area.
According to reports, 7 people have died while 3 people have sustained injuries due to the eruption. The Ministry confirmed that inhabitants of the area have been moved to safer locations while at the same time they are being given basic provisions.
Nabro began erupting on Sunday 12 June, 2011, the first ever recorded eruption of the stratovolcano. The resultant ash plume, extending up to 15km into the air, led to some flight cancellations in neighbouring Sudan, Djibouti and Ethiopia. The ash cloud was carried as far away as Saudi Arabia, Israel, Turkmenistan, Somalia, the Central African Republic (CAR) and Egypt. A second eruption on Thursday 16th June sent a massive ash plume westnorthwest over Sudan threatening to bring further disruption to air traffic in the east Africa region. The volcano has continued to emit varying amounts of ash, SO2 and water vapour since..
Part of the Afar Triangle, Nabro is one of many volcanic caldera complexes in the north easternmost part of the East African Rift valley region. The stratovolcano is located in the Danakil Depression, close to Eritrea’s border with Ethiopia and north of Djibouti, and has not erupted in at least 150 years. According to data, a similar volcanic eruption in Eritrea occurred in 1861, in Dubbi, Southern Denkel.
Nabro is the most prominent of 3 large volcanoes (Nabro, Dubbi, Mallahle) in the region, each containing a large summit caldera. Nabro comprises lava domes, lava flows, and two calderas, 8 and 5 km in diameter.
The volcano is located along the Great Rift Valley, also known as the East African Rift. the divergent plate boundary extends from the Afar Triple Junction southward across eastern Africa, and is in the process of splitting the African Plate into two new separate plates, the Nubian Plate and the Somali Plate. Seismic activity is frequent in Ethiopia In 1961 alone three thousand tremors were recorded from the centre of the Wollo province resulting in a 20km fissure being opened on the slopes of the Borkena graben.
A volcano that erupted for the first time in recorded history more than two weeks ago is continuing to emit large volumes of ash and sulphur dioxide (SO2) into the skies over Eritrea and northern Ethiopia.
The Nabro stratovolcano, which is located close to Eritrea’s border with Ethiopia in northeast Africa, temporarily affected air traffic two weeks ago when the ash plume drifted as far away as Israel, Jordan, Turmenistan and the Central African Republic (CAR).
Images from the MODIS satellite showed a thick ash plume drifting over Eritrea’s border into Ethiopia Monday afternoon. The volcanic ash was drifting SSW. Winds in the region were light NNE when the below images were captured at midday Monday.
Meanwhile, the eruption of the stratovolcano has created a new landmass, according to the director general of Mines at the Ministry of Energy and Mines, Mr. Alem Kibreab. Mr. Alem said that the ash and lava emitted from the Southern Red Sea region volcano has created a new land mass measuring hundreds of square metres. The director general also disclosed that a team composed of geological and volcanic experts is conducting studies in the area.
According to reports, 7 people have died while 3 people have sustained injuries due to the eruption. The Ministry confirmed that inhabitants of the area have been moved to safer locations while at the same time they are being given basic provisions.
Nabro began erupting on Sunday 12 June, 2011, the first ever recorded eruption of the stratovolcano. The resultant ash plume, extending up to 15km into the air, led to some flight cancellations in neighbouring Sudan, Djibouti and Ethiopia. The ash cloud was carried as far away as Saudi Arabia, Israel, Turkmenistan, Somalia, the Central African Republic (CAR) and Egypt. A second eruption on Thursday 16th June sent a massive ash plume westnorthwest over Sudan threatening to bring further disruption to air traffic in the east Africa region. The volcano has continued to emit varying amounts of ash, SO2 and water vapour since..
Part of the Afar Triangle, Nabro is one of many volcanic caldera complexes in the north easternmost part of the East African Rift valley region. The stratovolcano is located in the Danakil Depression, close to Eritrea’s border with Ethiopia and north of Djibouti, and has not erupted in at least 150 years. According to data, a similar volcanic eruption in Eritrea occurred in 1861, in Dubbi, Southern Denkel.
Nabro is the most prominent of 3 large volcanoes (Nabro, Dubbi, Mallahle) in the region, each containing a large summit caldera. Nabro comprises lava domes, lava flows, and two calderas, 8 and 5 km in diameter.
The volcano is located along the Great Rift Valley, also known as the East African Rift. the divergent plate boundary extends from the Afar Triple Junction southward across eastern Africa, and is in the process of splitting the African Plate into two new separate plates, the Nubian Plate and the Somali Plate. Seismic activity is frequent in Ethiopia In 1961 alone three thousand tremors were recorded from the centre of the Wollo province resulting in a 20km fissure being opened on the slopes of the Borkena graben.
Friday, June 24, 2011
Red alert as 'cork' plugs volcano
SMH.com.au: Red alert as 'cork' plugs volcano
Chilean experts have warned that a ''cork'' of lava could lead to another explosion at the Puyehue volcano, which has caused major flight disruptions from Argentina to Australia.
Seismic activity has declined, with two tremors of a magnitude of about 2.5 recorded every hour on Tuesday, compared with several hundred of a magnitude four or five in the hours preceding the initial June 4 eruption.
But Chile's National Service of Geology and Mining said on Wednesday that the volcano had to be kept on red alert because of the possibility of another explosion.
Geologists said a ''cork'' of lava, which emerged on Tuesday and was blocking even more lava from spewing forth, had the potential to create a huge build-up in pressure. If this continues, ''an explosive event remains possible, because the path the lava is taking is obstructed''.
Chilean experts have warned that a ''cork'' of lava could lead to another explosion at the Puyehue volcano, which has caused major flight disruptions from Argentina to Australia.
Seismic activity has declined, with two tremors of a magnitude of about 2.5 recorded every hour on Tuesday, compared with several hundred of a magnitude four or five in the hours preceding the initial June 4 eruption.
But Chile's National Service of Geology and Mining said on Wednesday that the volcano had to be kept on red alert because of the possibility of another explosion.
Geologists said a ''cork'' of lava, which emerged on Tuesday and was blocking even more lava from spewing forth, had the potential to create a huge build-up in pressure. If this continues, ''an explosive event remains possible, because the path the lava is taking is obstructed''.
Wednesday, June 22, 2011
Chilean Volcano Colors Southern Hemisphere Skies
Our Amazing Planet: Chilean Volcano Colors Southern Hemisphere Skies
After lying dormant for decades, Chile's Puyehue-Cordon Caulle volcano suddenly erupted on June 4 and has since hurled a tremendous cloud of ash, as well as plumes of sulfur dioxide into the air. This material has been circling the Southern Hemisphere and has been seriously disrupting air traffic for most of South America, and as far away as Australia and New Zealand.
But along with these negative aspects, the volcano has also been responsible for producing very colorful displays of deep reds and purplish hues as well as ripples of white both at dawn and dusk for many localities south of the equator.
This phenomenon of volcanic material coloring the twilight sky is well known and has been observed many times before in the aftermath of major eruptions. But just why does this occur? Before getting into an explanation, we should first explain how light is scattered to produce the various colors we see in our daytime sky. [See photos of the ash-colored sunsets.]
Sky colors
Why is the sky blue? That question was a befuddling one for a very long time. Around 1500, Leonardo da Vinci noticed that when white light passed through a cloud of smoke it appeared to have a bluish hue, but didn't make any connection with the color of the daytime sky.
Isaac Newton thought the color was due to the reflection of sunlight off of hollow water droplets, but this was wrong since hollow water droplets or bubbles do not occur in Earth's atmosphere. Then, in 1847, a German researcher, Ernst von Brücke performed a simple experiment with light passing through a cloud of smoke and observed that the light took on a bluish color similar to what da Vinci saw, and realized that it might have something to do with the color of the sky, but he couldn't prove it.
Finally, in 1881, John William Strutt, 3rd Baron Rayleigh (now known in most circles simply as Lord Rayleigh), provided the explanation: The blue color of the sky is due to air molecules which can scatter (or reflect) the light waves that pass by. If there were no air molecules, the sky would appear as black as night, and the stars would be visible even during the daylight hours. The sun would appear even brighter than it is now. Sky light is due to countless billions of air molecules and other minute dust particles called aerosols that scatter sunlight so that it can reach our eyes from all directions.
The sky appears blue because air molecules scatter blue light more easily. This is because the air molecules are far smaller than light waves. "Selective scattering," also known as Rayleigh scattering, is used to describe scattering that varies with the wavelength of the incident light. Atmospheric particles are good Rayleigh scatterers when they are very small compared to the wavelength of the light. Most light waves can easily bypass these tiny molecules and continue on their way. However, the shorter the wavelength of light, the more difficulty it will have in bypassing the molecules and the more likely that it will strike the molecules and be scattered in some other direction.
Add a volcano
The fine ash injected by a volcanic eruption into the stratosphere can be carried by winds all over the world and exist as thin veils of dust or sulfuric acid droplets (also called sulfate aerosols) at altitudes generally between 12 to 18 miles (19 to 29 kilometers). Now when the sun sets, its rays have more atmosphere to travel though to reach our eyes, so more of the long-wavelength red light can make the journey. Sulfate aerosols add more obstacles for the light to get through and as a result the effect of sky light that is directed more toward the red end of the spectrum becomes accentuated.
The beautiful colorations associated with the Puyehue-Cordon Caulle volcano might persist for quite some time to come. Experts from Chile's national service of geology and mining have said the volcano shows no sign of stabilizing. If the eruptions intensify, it could increase the amount of ash spewed up into the stratosphere. So for those living south of the equator, the colorful sunrises and sunsets which started appearing a couple of weeks ago might indeed continue for a number of days and even weeks or months.
In addition, Chilean volcanoes tend to spew more ash than North American or European volcanoes (such as Alaska’s Kasatochi or Iceland's Grimsvotn) because the magma is thicker and rises more slowly, resulting in more ash being expelled. Chile's chain of about 2,000 volcanoes is the world's second-largest after Indonesia. Some 50 to 60 volcanoes are on record as having erupted, and 500 are potentially active.
Other effects
Another unusual sight that southern skywatchers might look for is a diffuse halo of light, called a Bishop's Ring around the sun and moon, which occur when the aerosols diffract the light from either source. The first recorded observation of a Bishop's Ring was by Rev. Sereno Bishop of Honolulu, after the stupendous eruption of the Krakatoa volcano of 1883. The inner rim of the ring tends to appear bluish white while the outer part of the ring is tinted in hues of browns, reds or even purple. The area of the sky enclosed by the ring is significantly brighter than its surroundings.
Deep-red sunsets and Bishop's Rings were also widely seen after the massive eruption of the Philippines' Mount Pinatubo volcano in 1991, though that eruption was on a far larger scale than Puyehue-Cordon Caulle. In fact, the ash and aerosols that spewed from Mount Pinatubo covered much of the Northern Hemisphere for a couple of years acting almost like a gigantic sunscreen; they were so pervasive that global temperatures in the year after the eruption were cooler than normal.
After lying dormant for decades, Chile's Puyehue-Cordon Caulle volcano suddenly erupted on June 4 and has since hurled a tremendous cloud of ash, as well as plumes of sulfur dioxide into the air. This material has been circling the Southern Hemisphere and has been seriously disrupting air traffic for most of South America, and as far away as Australia and New Zealand.
But along with these negative aspects, the volcano has also been responsible for producing very colorful displays of deep reds and purplish hues as well as ripples of white both at dawn and dusk for many localities south of the equator.
This phenomenon of volcanic material coloring the twilight sky is well known and has been observed many times before in the aftermath of major eruptions. But just why does this occur? Before getting into an explanation, we should first explain how light is scattered to produce the various colors we see in our daytime sky. [See photos of the ash-colored sunsets.]
Sky colors
Why is the sky blue? That question was a befuddling one for a very long time. Around 1500, Leonardo da Vinci noticed that when white light passed through a cloud of smoke it appeared to have a bluish hue, but didn't make any connection with the color of the daytime sky.
Isaac Newton thought the color was due to the reflection of sunlight off of hollow water droplets, but this was wrong since hollow water droplets or bubbles do not occur in Earth's atmosphere. Then, in 1847, a German researcher, Ernst von Brücke performed a simple experiment with light passing through a cloud of smoke and observed that the light took on a bluish color similar to what da Vinci saw, and realized that it might have something to do with the color of the sky, but he couldn't prove it.
Finally, in 1881, John William Strutt, 3rd Baron Rayleigh (now known in most circles simply as Lord Rayleigh), provided the explanation: The blue color of the sky is due to air molecules which can scatter (or reflect) the light waves that pass by. If there were no air molecules, the sky would appear as black as night, and the stars would be visible even during the daylight hours. The sun would appear even brighter than it is now. Sky light is due to countless billions of air molecules and other minute dust particles called aerosols that scatter sunlight so that it can reach our eyes from all directions.
The sky appears blue because air molecules scatter blue light more easily. This is because the air molecules are far smaller than light waves. "Selective scattering," also known as Rayleigh scattering, is used to describe scattering that varies with the wavelength of the incident light. Atmospheric particles are good Rayleigh scatterers when they are very small compared to the wavelength of the light. Most light waves can easily bypass these tiny molecules and continue on their way. However, the shorter the wavelength of light, the more difficulty it will have in bypassing the molecules and the more likely that it will strike the molecules and be scattered in some other direction.
Add a volcano
The fine ash injected by a volcanic eruption into the stratosphere can be carried by winds all over the world and exist as thin veils of dust or sulfuric acid droplets (also called sulfate aerosols) at altitudes generally between 12 to 18 miles (19 to 29 kilometers). Now when the sun sets, its rays have more atmosphere to travel though to reach our eyes, so more of the long-wavelength red light can make the journey. Sulfate aerosols add more obstacles for the light to get through and as a result the effect of sky light that is directed more toward the red end of the spectrum becomes accentuated.
The beautiful colorations associated with the Puyehue-Cordon Caulle volcano might persist for quite some time to come. Experts from Chile's national service of geology and mining have said the volcano shows no sign of stabilizing. If the eruptions intensify, it could increase the amount of ash spewed up into the stratosphere. So for those living south of the equator, the colorful sunrises and sunsets which started appearing a couple of weeks ago might indeed continue for a number of days and even weeks or months.
In addition, Chilean volcanoes tend to spew more ash than North American or European volcanoes (such as Alaska’s Kasatochi or Iceland's Grimsvotn) because the magma is thicker and rises more slowly, resulting in more ash being expelled. Chile's chain of about 2,000 volcanoes is the world's second-largest after Indonesia. Some 50 to 60 volcanoes are on record as having erupted, and 500 are potentially active.
Other effects
Another unusual sight that southern skywatchers might look for is a diffuse halo of light, called a Bishop's Ring around the sun and moon, which occur when the aerosols diffract the light from either source. The first recorded observation of a Bishop's Ring was by Rev. Sereno Bishop of Honolulu, after the stupendous eruption of the Krakatoa volcano of 1883. The inner rim of the ring tends to appear bluish white while the outer part of the ring is tinted in hues of browns, reds or even purple. The area of the sky enclosed by the ring is significantly brighter than its surroundings.
Deep-red sunsets and Bishop's Rings were also widely seen after the massive eruption of the Philippines' Mount Pinatubo volcano in 1991, though that eruption was on a far larger scale than Puyehue-Cordon Caulle. In fact, the ash and aerosols that spewed from Mount Pinatubo covered much of the Northern Hemisphere for a couple of years acting almost like a gigantic sunscreen; they were so pervasive that global temperatures in the year after the eruption were cooler than normal.
Monday, June 20, 2011
Iceland volcano farmer thankful for ash cover
Ice News: Iceland volcano farmer thankful for ash cover
Hay making began near the Eyjafjallajokull glacier, site of the 2010 volcanic eruption, this Wednesday — a week earlier than last year. The farmer at Thorvaldseyri says the ash has saved a lot of money on fertiliser and that the best grass is growing where the most ash fell.
The farmer, Olafur Eggertsson, was surrounded by freshly cut hay when Visir.is contacted him on Wednesday. He reported that the grass growing season has been slow to start, “It has of course been unusually cold here like elsewhere, but now in recent days it has grown very fast and the little bit of rain we had made a massive difference”.
He was afraid that the massive amount of volcanic ash that fell from Eyjafjallajokull last year would have a long-term negative impact on his hay grass. “But it actually seems it has a positive long-term effect and we are seeing very nice grass which is only receiving half the usual dose of fertiliser,” Eggertsson said. “There is great saving to be made there and despite the very cold spring it is an okay time, now in mid-June, to be cutting this good grass.”
The tale of optimism from Eyjafjallajokull will come as pleasant news to farmers near the Vatnajokull glacier, under which the Grimsvotn volcano erupted earlier this year.
Toronto Sun: Chilean volcano evacuees return as eruption eases
A volcanic eruption in southern Chile that sent a plume of ash circling the globe and caused air traffic chaos has eased, allowing more than 4,200 evacuees to return home, the government said Sunday.
Airborne ash from the volcano in Chile’s Puyehue-Cordon Caulle chain, which erupted on June 4 after decades of dormancy, was carried around the world by winds.
The fine particles, which can damage jet engines, forced the sporadic cancellation of hundreds of flights from Argentina to Australia in recent weeks.
Ash could potentially hamper flights for months, experts said.
But a decrease in the force of the eruption has raised hopes the situation is stabilizing.
That was good news for more than 4,200 people who were evacuated.
“We have decided those who had to evacuate can return to their homes, because the volcanic activity is decreasing,” Interior Minister Rodrigo Hinzpeter told a news conference.
He said, however, the volcano would likely emit ash for some time. The eruption sent an ash cloud up to 20 miles into the atmosphere.
The air traffic chaos in South America buffeted operations at carriers, including Chile’s LAN, Brazil’s TAM and Gol.
LAN briefly interrupted domestic Chilean flights south to Patagonia on Friday, before resuming service.
Iceland’s most active volcano at Grimsvotn sent a thick plume of ash and smoke 15.5 miles into the sky last month, disrupting air travel in northern Europe and Britain.
The eruption of another Icelandic volcano in April 2010, Eyjafjallajokull, led to 100,000 canceled flights, affecting 10 million people at a cost of $1.7 billion.
The Chilean eruption has also coated tourist towns in southern Argentina with gray ash, impacting livestock and deterring visitors during the lucrative winter season.
It was the latest in a series of volcanic eruptions in Chile in recent years. Chile’s Chaiten volcano erupted spectacularly in 2008 for the first time in thousands of years, spewing molten rock and a vast cloud of ash that reached the stratosphere.
The Llaima volcano, one of South America’s most active, erupted in 2008 and 2009.
Chile’s chain of about 2,000 volcanoes is the world’s second-largest after Indonesia’s. Some 50 to 60 are on record as having erupted, and 500 are potentially active.
Feature of the Week: Crater in One
Iceland Review: Feature of the Week: Crater in One
In the crater of a volcano, on a black sandy beach, under a glacier… in Iceland, golfing is always in touch with nature.See link for complete article
Published in the No. 3 2011 June-July issue of Atlantica. By Sari Peltonen, photos by Páll Stefánsson.
Waves crash against the rocks. North-Atlantic winds tear at trousers and sleeves. The view from the tee opens onto an 11,000-year-old volcanic crater. High up the hillside, little more than white dots, is the audience—a flock of daredevil sheep. Welcome to golf, the Westman Islands way.
This cluster of 18 islands, located a stones-throw from the mainland, was birthed by underwater volcanic eruptions. The Heimaey fishing community has a dramatic past: One January night in 1973, without warning, the volcano Eldfell erupted. Entirely unexpected, it was only thanks to the town’s fishing fleet that the inhabitants managed to miraculously escape the cataclysm. Nonetheless the village was buried in ash, with some of the houses remaining underground to this day.
Ash also covered the golf course on the outskirts of the village, but it was dug up immediately after the 5-month-long eruption finished. Life only goes on if the golfing does too. Built in 1939, the Heimaey course is one of the oldest in Iceland and hole 17 is a local legend. To reach the green one must hit the ball across the Atlantic, crosswind and all. Reports that golfers can now cross the ocean on a bridge of balls driven too short are unconfirmed.
THE NATIONAL SPORT
An 18-hole course in a volcanic crater outside a village of 2,000 fishermen is the perfect illustration of Icelandic golf culture. The second most popular sport after football, over 10% of the nation tees off five times a year or more (2009). The golf union was established in 1942, and its membership figures have grown steadily ever since. In 2010, there were over 13,000 registered amateur golfers (4% of the population).
Golf courses are built everywhere: in a geothermal valley where hot springs steam on the hillsides; on a beach where rough means one large bunker of black volcanic sand; in the bay of a desolate fjord. In total there are currently 65 golf courses in Iceland. One of them has 27 holes, fifteen are full 18-hole courses and the rest are 9-hole courses. In relation to the number of inhabitants (320,000), there are more golf courses in Iceland than anywhere else in the world; one for every 5,000 Icelanders.
Friday, June 17, 2011
Kizimen, Karymsky volcanoes spew ash in Russia
UPI.com: Kizimen, Karymsky volcanoes spew ash in Russia
MOSCOW, June 17 (UPI) -- The Kizimen and Karymsky volcanoes on Russia's Kamchatka Peninsula spewed ash and gas, accompanied by earth tremors, a Russian science agency said Friday.
A spokesman for the Geophysical Service of the Russian Academy of Sciences said as many as 400 tremors have been registered, ITAR-Tass reported Friday.
The "orange" aviation alert code was activated, warning of the danger volcanic dust and emitted gases can pose to aircraft, officials said.
Rising to an altitude of 7,795 feet, the Kizimen volcano is about 265 kilometers from Petropavlovsk-Kamchatsky. Geologists estimate the volcano formed about 12,000 years ago.
One of 29 active volcanoes on the Kamchatka peninsula, Kizimen was violent in 1928 and 1929. It began to exhibit activity again in 2009.
The 4,875-foot Karymsky is the most active volcano of Kamchatka's eastern volcanic zone and a symmetrical stratovolcano, the academy spokesman said. Its activity increased dramatically in 1996 and still erupts periodically.
MOSCOW, June 17 (UPI) -- The Kizimen and Karymsky volcanoes on Russia's Kamchatka Peninsula spewed ash and gas, accompanied by earth tremors, a Russian science agency said Friday.
A spokesman for the Geophysical Service of the Russian Academy of Sciences said as many as 400 tremors have been registered, ITAR-Tass reported Friday.
The "orange" aviation alert code was activated, warning of the danger volcanic dust and emitted gases can pose to aircraft, officials said.
Rising to an altitude of 7,795 feet, the Kizimen volcano is about 265 kilometers from Petropavlovsk-Kamchatsky. Geologists estimate the volcano formed about 12,000 years ago.
One of 29 active volcanoes on the Kamchatka peninsula, Kizimen was violent in 1928 and 1929. It began to exhibit activity again in 2009.
The 4,875-foot Karymsky is the most active volcano of Kamchatka's eastern volcanic zone and a symmetrical stratovolcano, the academy spokesman said. Its activity increased dramatically in 1996 and still erupts periodically.
Chile volcano ash circles globe, returns home
SFGate: Chile volcano ash circles globe, returns home
The ash cloud from a Chilean volcano that has been erupting for nearly two weeks has circled the globe and come home again.
The returning cloud — which has disrupted flights in Argentina, Brazil, Uruguay, Australia and New Zealand on its around-the-world trip — on Friday forced Chilean officials to cancel domestic flights for the first time since the Cordon Caulle volcano began erupting June 4.
LAN airlines suspended flights to the cities of Puerto Montt, Coyhaique and Punta Arenas in the far south of the South American country. While ash from Cordon Caulle has wreaked havoc with air travel abroad, it had left Chile's internal flights largely untouched until Friday.
"The tip of the cloud that has traveled around the world is more or less in front of Coyhaique," said Civil Aviation Office chief Pablo Ortega. Coyhaique is 800 kilometers (500 miles) south of the volcano.
Chilean authorities evacuated 3,500 people living near the volcano after it began erupting but some have since returned.
The governor of Ranco province, Eduardo Holck, said the volcano is emitting a fine ash that is scattering over the Nilahue river valley.
The government, however, maintained a red alert for communities near Cordon Caulle. Chile's National Geology and Mines Service warned that volcanic activity could begin again "with episodes similar or greater in intensity that was has occurred."
On Thursday, the government of the Argentine province of Neuquen declared an economic emergency to aid towns where falling ash from Chile's volcano is endangering livestock and keeping tourists away.
The decree by Gov. Jorge Sapag will mean that those affected can receive tax benefits, among other measures.
The ash has blanketed towns across the border in Argentina.
In the area of Villa La Angostura up to one foot (30 centimeters) of ash has accumulated on the ground. The eruption came just as resorts in the mountain towns were preparing for ski season.
Argentina's regional airports in Patagonia have also been shut down for more than a week due to the cloud of fine grit, which can damage airplane engines.
The ash cloud from a Chilean volcano that has been erupting for nearly two weeks has circled the globe and come home again.
The returning cloud — which has disrupted flights in Argentina, Brazil, Uruguay, Australia and New Zealand on its around-the-world trip — on Friday forced Chilean officials to cancel domestic flights for the first time since the Cordon Caulle volcano began erupting June 4.
LAN airlines suspended flights to the cities of Puerto Montt, Coyhaique and Punta Arenas in the far south of the South American country. While ash from Cordon Caulle has wreaked havoc with air travel abroad, it had left Chile's internal flights largely untouched until Friday.
"The tip of the cloud that has traveled around the world is more or less in front of Coyhaique," said Civil Aviation Office chief Pablo Ortega. Coyhaique is 800 kilometers (500 miles) south of the volcano.
Chilean authorities evacuated 3,500 people living near the volcano after it began erupting but some have since returned.
The governor of Ranco province, Eduardo Holck, said the volcano is emitting a fine ash that is scattering over the Nilahue river valley.
The government, however, maintained a red alert for communities near Cordon Caulle. Chile's National Geology and Mines Service warned that volcanic activity could begin again "with episodes similar or greater in intensity that was has occurred."
On Thursday, the government of the Argentine province of Neuquen declared an economic emergency to aid towns where falling ash from Chile's volcano is endangering livestock and keeping tourists away.
The decree by Gov. Jorge Sapag will mean that those affected can receive tax benefits, among other measures.
The ash has blanketed towns across the border in Argentina.
In the area of Villa La Angostura up to one foot (30 centimeters) of ash has accumulated on the ground. The eruption came just as resorts in the mountain towns were preparing for ski season.
Argentina's regional airports in Patagonia have also been shut down for more than a week due to the cloud of fine grit, which can damage airplane engines.
Tuesday, June 14, 2011
Volcanology: Shield Volcanos
A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes. This results in the steady accumulation of broad sheets of lava, building up the shield volcano's distinctive form.
Etymology
Shield volcanoes are built up by effusive eruptions, which flow out in all directions to create a shield like that of a warrior. The word shield has a long history, and is derived from the Old English scield or scild, which is in turn taken from the Proto-Germanic skeldus taken from various derivations of the Gothic skildus, meaning "to divide, split, or separate". Shield volcano itself is taken from the German term schildvulkan.
Geology
Shield volcanoes are one of the three major types of volcanoes, distinguished from the two other major volcanic types, stratovolcanoes and cinder cones, by distinct differences in structure and composition.
Stratovolcanoes are built up by the accumulation of thick, viscous lavas, whereas cinder cones are constructed of tephra ejected in explosive eruptions. In comparison, shield volcanoes are built of relatively weakly viscous basaltic lavas that erupts in longer cycles than that of a stratovolcano. Shield volcanoes are distinctive products of hotspot volcanism, but can form at rift and subduction zones as well.
The types of eruptions that occur at shield volcanoes have been named Hawaiian eruptions, after the Hawaiian chain in which they are most prominent. Hawaiian eruptions are characterized by the effusive emission of fluid lavas.
The mobile nature of these lavas allows shield volcano flows to travel a longer distance than those of other volcanic types, resulting in a larger and thinner sheets of lava, often just 1 m (3 ft) thick. Over long periods of time, the gradual buildup of thousands of these flows slowly constructs the characteristically low, broad profile of a mature shield volcano.
Because of their gradual buildup and near-continuous eruptive characteristics, shield volcanoes vary widely in size with their age. Mature shield volcanoes are the largest volcanoes on Earth. Shield volcanoes often measure 3 to 4 mi (5 to 6 km) in diameter and surpass 1,500 to 2,000 ft (460 to 610 m) in height. The largest shield volcano (and the largest active volcano) in the world is Mauna Loa in Hawaiʻi, which projects 13,677 ft (4,169 m) above sea level, and is over 60 mi (97 km) wide.
The volcano is estimated to contain 80,000 km3 (19,000 cu mi) of basalt,[6] a mass is so great that it has slumped into the Earth's crust. Their lower slopes are generally gentle (~2 degrees), but steepen with elevation (reaching ~10 degrees) before flattening near the summit, giving the volcanoes a convex shape. The height of a shield volcano is typically 1/20th of its width.
The Hawaiian shield volcanoes and the Galápagos islands are unique in that they are not located near any plate boundaries; instead, the two chains are fed by the movement of oceanic plates over an upwelling of magma known as a hotspot. Over millions of years, the tectonic movement that moves continents also creates long volcanic trails across the seafloor. The Hawaiian and Galápagos shields, and other hotspot shields like them, are both constructed of oceanic island basalt. Their lavas are characterized by high levels of sodium, potassium, and aluminum.
Rift zones are a prevalent feature on shield volcanoes that is rare on other volcanic types. The large, decentralized shape of Hawaiian volcanoes as compared to their smaller, symmetrical Icelandian cousins can be attributed to rift eruptions. Fissure venting is common in Hawaiʻi; most Hawaiian eruptions begin with a so-called "wall of fire" along a major fissure line before centralizing to a small number of points. This accounts for their asymmetrical shape, whereas Icelandian volcanoes follow a pattern of central eruptions dominated by summit calderas, causing much evener lava.
Another hallmark of shield volcanism are lava tubes. Lava tubes are cave-like volcanic straights formed by the hardening of overlaying lava. These structures help further the propagation of lava, as the walls of the tube insulates the lava within. Lava tubes can account for a large chunk of shield volcano activity; for example, an estimated 58% of the lava forming Kilauea comes from lava tubes.
Most mature shield volcanoes have multiple splatter (or cinder) cones on their flanks. The cones are a result of tephra ejection during incessant activity, building up a volcanic cone at the eruption site, and thus marking the site of former and current eruptive sites on the shield volcano. A prominent example of a shield volcano-bound cinder cone is is Puʻu ʻŌʻō on Kīlauea. The cone has been erupting continuously since 1983 in one of the longest-lasting rift eruptions in history, and was built up to its present height of 2,290 ft (698 m) by over 25 years of activity.
In some shield volcano eruptions, basaltic lava pours out of a long fissure instead of a central vent, and shrouds the countryside with a long band of volcanic material in the form of a broud plateau. Plateaus of this type exist in Iceland, Washington, Oregon, and Idaho; the most prominent ones are situated along the Snake River in Idaho and the Columbia River in Washington and Oregon, where they have been measured to be over a 1 mi (2 km) in thickness. Many eruptions start as a so-called "curtain of fire"—a long eruptive chain along a fissure vent on the volcano. Eventually these eruptions die down and start to focus around a few points on the fissure, where activity is concentrated.
Calderas are a common feature on shield volcanoes. They are formed and reformed over the volcano's lifespan. Long eruptive periods form cinder cones, which then collapse over time to form calderas. The calderas are often filled up by future eruptions, or formed elsewhere, and this cycle of collapse and regeneration takes place throughout the volcano's lifespan.
Interactions between water and lava at shield volcanoes can cause some eruptions to become hydrovolcanic. These explosive eruptions are drastically different from the usual shield volcanic activity, and are especially prevalent at the waterbound volcanoes of the Hawaiian Isles.
Distribution
Shield volcanoes are found worldwide. They can form over hotspots (points where magma from below the surface wells up), such as the Hawaiian-Emperor seamount chain and the Galápagos Islands, or over more conventional rift zones, such as the Icelandic shields and the shield volcanoes of the shield volcanoes of East Africa. Many shield volcanoes are found in ocean basins, although they can be found inland as well—East Africa being one example of this.
Hawaiian islands
Mauna Kea, Hawaiʻi, the largest volcano on Earth.The largest and most prominent shield volcano chain in the world are the Hawaiian Islands, a chain of hotspot volcanoes in Pacific Ocean. The Hawaiian volcanoes are characterized by frequent rift eruptions, their large size (thousands of km3 in volume), and their rough, decentralized shape. Rift zones are a prominent feature on these volcanoes, and account for their seemingly random volcanic structure.
They are fueled by the movement of the Pacific Plate over the Hawaii hotspot, and form a long chain of volcanoes, atolls, and seamounts 2,600 km (1,616 mi) long with a total volume of over 750,000 km3 (179,935 cu mi). The chain contains at least 43 major volcanoes, and Meiji Seamount at its terminus near the Kuril-Kamchatka Trench is 85 million years old. The volcanoes follow a distinct evolutionary pattern of growth and death.
The chain includes the largest volcano on Earth, Mauna Loa, which stands 4,170 m (13,680 ft) above sea level and reaches a further 13 km (8 mi) below the waterline and into the crust, approximately 80,000 km3 (19,000 cu mi) of rock. Kilauea, meanwhile, is one of the most active volcanoes on Earth, with the current ongoing eruption having begun in January 1983.
Galápagos islands
An animated tour of the Galápagos Islands.The Galápagos Islands are an isolated set of volcanoes, consisting of shield volcanoes and lava plateaus, located 1,200 km (746 mi) west of Ecuador. They are driven by the Galápagos hotspot, and are between approximately 4.2 million and 700,000 years of age.
The largest island, Isabela Island, consists of six coalesced shield volcanoes, each delineated by a large summit caldera. Española, the oldest island, and Fernandina, the youngest, are also shield volcanoes, as are most of the other islands in the chain.
The Galápagos Islands are perched on a large lava plateau known as the Galápagos Platform. This platform creates a shallow water depth of 360 to 900 m (1,181 to 2,953 ft) at the base of the islands, which stretch over a 174 mi (280 km)-long diameter. Since Charles Darwin's famous visit to the islands in 1835, there have been over 60 recorded eruptions in the islands, from six different shield volcanoes. Of the 21 emergent volcanoes, 13 are considered active.
The Galápagos islands are geologically young for such a large chain, and the pattern of their rift zones follows one of two trends, one north-northwest, and one east-west. The composition of the lavas of the Galápagos shields are strikingly similar to those of the Hawaiian volcanoes. Curiously, they do not form the same volcanic "line" associated with most hotspots.
They are not alone in this regard; the Cobb-Eickelberg Seamount chain in the North Pacific is another example of such a delineated chain. In addition, there is no clear pattern of age between the volcanoes, suggesting a complicated, irregular pattern of creation. How exactly the islands were formed remains a geological mystery, although several theories have been fronted.
Iceland
Skjaldbreiður, Iceland, is eponymous for shield volcanoes. Another major center of shield volcanic activity is Iceland. Located over the Mid-Atlantic Ridge, a divergent tectonic plate in the middle of the Atlantic Ocean, Iceland is the site of about 130 volcanoes of various types.
Icelandic shield volcanoes are generally of Holocene age, between 5000 and 10000 years old, except for the island of Surtsey, a Surtseyan shield. The volcanoes are also very narrow in distribution, occurring in two bands in the West and North Volcanic Zones. Like Hawaiian volcanoes, their formation initially begins with several eruptive centers before centralizing and concentrating at a single point. The main shield then forms, burying the smaller ones formed by the early eruptions with its lava.
Icelandic shields are generally small (~15 km3 (4 cu mi)), symmetrical (although this can affected by surface topography), and characterized by eruptions from summit calderas. They are composed of either tholeiitic olivine or picritic basalt. The tholeiitic shields tend to be wider and shallower than the picritic shields. They do not follow the pattern of caldera growth and destruction that other shield volcanoes do; caldera may form, but they generally do not disappear. None of the shield volcanoes in the region are known to have erupted within the last 5000 years.
East Africa
East Africa is the site of volcanic activity generated by the development of the East African Rift, a developing plate boundary in Africa, and from nearby hotspots. Some volcanoes interact with both. Shield volcanoes are found near the rift and off the coast of Africa, although stratovolcanoes are more common. Although sparsely studied, the fact that all of its volcanoes are of Holocene age reflects how young the volcanic center is. One interesting characteristic of East African volcanism is a penchant for the formation of lava lakes; these semi-permanent lava bodies, extremely rare elsewhere, form in about 9% of African eruptions.
The most active shield volcano in Africa is Nyamuragira. Eruptions at the shield volcano are generally centered within the large summit caldera or on the numerous fissures and cinder cones on the volcano's flanks. Lava flows from the most recent century extend down the flanks more than 30 km (19 mi) from the summit, reaching as far as Lake Kivu. Erta Ale in Ethiopia is another active shield volcano, and one of the few places in the world with a permanent lava lake, which has been active since at least 1967, and possibly since 1906. Other volcanic centers include Menengai, a massive shield caldera, and Mount Marsabit, near the town of Marsabit.
The volcanoes of Mars are very similar to the shield volcanoes on Earth. Both have gently sloping flanks, collapse craters along their central structure, and are built of highly fluid lavas. Volcanic features on Mars were observed long before they were first studied in detail during the 1976-1979 Viking mission. The principal difference between the volcanoes of Mars and those on Earth is in terms of size; Martian volcanoes are over 17 mi (27 km) high and 350 mi (563 km) in diameter, far larger than the 6 mi (10 km) high, 74 mi (119 km) wide Hawaiian shields. The most famous example is Olympus Mons, a shield volcano that is the highest known mountain in the solar system.
Venus also has over 150 shield volcanoes which are much flatter, with a larger surface area than those found on Earth, some having a diameter of more than 700km (435 miles). Although the majority of these are long extinct it has been suggested, from observations by the Venus Express spacecraft that many may still be active.
Dangers
The Hawaiian eruptions of shield volcanoes do not pose much threat to humans, as they emit large amounts of slow moving lava over long periods of time. However, they are hazardous to agriculture and infrastructure; the ongoing 1983 eruption of Kīlauea has destroyed over 200 structures and buried kilometers of highways.
Pyroclastic shields
Rarer pyroclastic shield volcanoes are similar to normal mafic shields in shape. But rather than being formed entirely by basalt lavas, pyroclastic shields are mainly formed from explosive eruptions of ignimbrite.
Monday, June 13, 2011
Nabro Volcano - Eritrea
Nabro
Elevation 2,218 m (7,277 ft)
Type Stratovolcano
The Nabro Volcano is a stratovolcano located in the Northern Red Sea Region of Eritrea. It is located in the Danakil Depression.
Geology
Part of the Afar Triangle, the Nabro Volcano is one of many volcanic caldera complexes in the northeasternmost part of the East African Rift valley region. The twin calderas likely formed about during an eruption of about 20 to 100 cubic kilometres consisting of ignimbrite, although the date of their formation is unknown. The subaerial volume of volcanic material within the Nabro Volcanic Range mantle plume is likely on the order of 550 km3.
2011 eruption
Despite having undergone no eruptions in recent history, the Nabro Volcano likely erupted shortly after midnight on June 13, 2011 local time, after a series of earthquakes in the Eritrea-Ethiopia border region, ranging up to magnitude 5.7. The ash plume was observed on satellite drifting to the west-northwest along the border, and spanned about 50 km wide and several hundred kilometres across in the hours immediately following the reported eruption. The ash plume reportedly reached 8 miles (15km) high.
Elevation 2,218 m (7,277 ft)
Type Stratovolcano
The Nabro Volcano is a stratovolcano located in the Northern Red Sea Region of Eritrea. It is located in the Danakil Depression.
Geology
Part of the Afar Triangle, the Nabro Volcano is one of many volcanic caldera complexes in the northeasternmost part of the East African Rift valley region. The twin calderas likely formed about during an eruption of about 20 to 100 cubic kilometres consisting of ignimbrite, although the date of their formation is unknown. The subaerial volume of volcanic material within the Nabro Volcanic Range mantle plume is likely on the order of 550 km3.
2011 eruption
Despite having undergone no eruptions in recent history, the Nabro Volcano likely erupted shortly after midnight on June 13, 2011 local time, after a series of earthquakes in the Eritrea-Ethiopia border region, ranging up to magnitude 5.7. The ash plume was observed on satellite drifting to the west-northwest along the border, and spanned about 50 km wide and several hundred kilometres across in the hours immediately following the reported eruption. The ash plume reportedly reached 8 miles (15km) high.
Volcano eruption in Eritrea cuts short Hillary Clinton visit
The Telegraph: Volcano eruption in Eritrea cuts short Hillary Clinton visit
By Aislinn Laing, Johannesburg
8:07PM BST 13 Jun 2011
The eruption of the Nabro volcano close to the east African country's border with Ethiopia came at around midnight local time on Sunday and was preceded by a series of earthquakes, the most powerful with a magnitude of 5.7 on the Richter scale.
Plumes of ash were sent eight miles upwards into the air. The ash cloud has already seen the cancellation of flights to Eritrea and neighbouring Ethiopia, and is expected to cause severe disruption in Saudi Arabia, Jordan and Israel, to the north.
Mrs Clinton arrived in Ethiopia today to address a meeting of the 53-member of the African Union and meet with Ethiopian Prime Minister Meles Zenawi.
But amid warnings that the Ethiopia's aviation authorities were considering closing Addis Ababa's main airport as the ash cloud headed to the capital, she cancelled a media briefing and flew home 24 hours early.
An official travelling with Mrs Clinton said they had been forced to make a snap decision or risk being stranded.
Volcano eruption in Eritrea cuts short Hillary Clinton visit
Hillary Clinton, the US Secretary of State, was forced to cut short a tour of Africa after an Eritrean volcano that has lain dormant since modern records began erupted.
Image 1 of 2
NASA image shows a plume of smoke from an erupting volcano in southern Eritrea, seen at top right, is carried by winds blowing across northern Ethiopia Photo: AP
Image 1 of 2Mrs Clinton arrived in Ethiopia today to address a meeting of the 53-member of the African Union and meet with Ethiopian Prime Minister Meles Zenawi Photo: REUTERS
By Aislinn Laing, Johannesburg
8:07PM BST 13 Jun 2011
The eruption of the Nabro volcano close to the east African country's border with Ethiopia came at around midnight local time on Sunday and was preceded by a series of earthquakes, the most powerful with a magnitude of 5.7 on the Richter scale.
Plumes of ash were sent eight miles upwards into the air. The ash cloud has already seen the cancellation of flights to Eritrea and neighbouring Ethiopia, and is expected to cause severe disruption in Saudi Arabia, Jordan and Israel, to the north.
Mrs Clinton arrived in Ethiopia today to address a meeting of the 53-member of the African Union and meet with Ethiopian Prime Minister Meles Zenawi.
But amid warnings that the Ethiopia's aviation authorities were considering closing Addis Ababa's main airport as the ash cloud headed to the capital, she cancelled a media briefing and flew home 24 hours early.
An official travelling with Mrs Clinton said they had been forced to make a snap decision or risk being stranded.
Related Articles
Volcanic ash from Chile grounds Australian flights
12 Jun 2011
Chile volcano eruption causes ash cloud
05 Jun 2011
Related Links
You might like:Scientists create cow that produces 'human' milk10 Jun 2011(Telegraph News)Duchess of Cambridge makes Prince William blush at Garter Day procession13 Jun 2011(Telegraph News)WikiLeaks: Hillary Clinton questions the mental health of Cristina Kirchner10 Jun 2011(Telegraph News)
From the WebFORM THE WEB:China Accuses U.S. of Launching Global 'Internet War' to Bring Down Arab Governments03 Jun 2011(FoxNews.com)Powerful quake rattles New Zealand city (Reuters)12 Jun 2011(Yahoo! News)White IPhone Sparks Skirmish at Beijing Apple Store09 May 2011(PC World)[what's this]"If the plane leaves without us, it's unclear when it or another plane could come get us because the ash cloud is moving towards Addis and it could cover the city for an indeterminate length of time," he said as the delegation departed. "Therefore (what we have decided) to do, which the air force is recommending, is to leave."
Mrs Clinton was not alone in having her plans disrupted by volcanoes this week. The continued eruption of Chile's Puyehue volcano, which has disrupted air travel from South America to Australia, forced a flight carrying Ban Ki-moon, the UN Secretary General, to divert to the northern Argentine city of Cordoba.
Mr Ban was forced to travel the remaining 400 miles to the capital Buenos Aires for a meeting with President Cristina Kirchner by car.
The 5,331ft Nabro volcano is close to Eritrea's border with Ethiopia and north of Djibouti, and has not erupted in at least 150 years.
It is located within the Danakil Depression, a junction of three tectonic plates spanning Eritrea and Ethiopia, whose spreading ridges could some 10 million years from now form a new ocean and split Africa in two.
By Aislinn Laing, Johannesburg
8:07PM BST 13 Jun 2011
The eruption of the Nabro volcano close to the east African country's border with Ethiopia came at around midnight local time on Sunday and was preceded by a series of earthquakes, the most powerful with a magnitude of 5.7 on the Richter scale.
Plumes of ash were sent eight miles upwards into the air. The ash cloud has already seen the cancellation of flights to Eritrea and neighbouring Ethiopia, and is expected to cause severe disruption in Saudi Arabia, Jordan and Israel, to the north.
Mrs Clinton arrived in Ethiopia today to address a meeting of the 53-member of the African Union and meet with Ethiopian Prime Minister Meles Zenawi.
But amid warnings that the Ethiopia's aviation authorities were considering closing Addis Ababa's main airport as the ash cloud headed to the capital, she cancelled a media briefing and flew home 24 hours early.
An official travelling with Mrs Clinton said they had been forced to make a snap decision or risk being stranded.
Volcano eruption in Eritrea cuts short Hillary Clinton visit
Hillary Clinton, the US Secretary of State, was forced to cut short a tour of Africa after an Eritrean volcano that has lain dormant since modern records began erupted.
Image 1 of 2
NASA image shows a plume of smoke from an erupting volcano in southern Eritrea, seen at top right, is carried by winds blowing across northern Ethiopia Photo: AP
Image 1 of 2Mrs Clinton arrived in Ethiopia today to address a meeting of the 53-member of the African Union and meet with Ethiopian Prime Minister Meles Zenawi Photo: REUTERS
By Aislinn Laing, Johannesburg
8:07PM BST 13 Jun 2011
The eruption of the Nabro volcano close to the east African country's border with Ethiopia came at around midnight local time on Sunday and was preceded by a series of earthquakes, the most powerful with a magnitude of 5.7 on the Richter scale.
Plumes of ash were sent eight miles upwards into the air. The ash cloud has already seen the cancellation of flights to Eritrea and neighbouring Ethiopia, and is expected to cause severe disruption in Saudi Arabia, Jordan and Israel, to the north.
Mrs Clinton arrived in Ethiopia today to address a meeting of the 53-member of the African Union and meet with Ethiopian Prime Minister Meles Zenawi.
But amid warnings that the Ethiopia's aviation authorities were considering closing Addis Ababa's main airport as the ash cloud headed to the capital, she cancelled a media briefing and flew home 24 hours early.
An official travelling with Mrs Clinton said they had been forced to make a snap decision or risk being stranded.
Related Articles
Volcanic ash from Chile grounds Australian flights
12 Jun 2011
Chile volcano eruption causes ash cloud
05 Jun 2011
Related Links
You might like:Scientists create cow that produces 'human' milk10 Jun 2011(Telegraph News)Duchess of Cambridge makes Prince William blush at Garter Day procession13 Jun 2011(Telegraph News)WikiLeaks: Hillary Clinton questions the mental health of Cristina Kirchner10 Jun 2011(Telegraph News)
From the WebFORM THE WEB:China Accuses U.S. of Launching Global 'Internet War' to Bring Down Arab Governments03 Jun 2011(FoxNews.com)Powerful quake rattles New Zealand city (Reuters)12 Jun 2011(Yahoo! News)White IPhone Sparks Skirmish at Beijing Apple Store09 May 2011(PC World)[what's this]"If the plane leaves without us, it's unclear when it or another plane could come get us because the ash cloud is moving towards Addis and it could cover the city for an indeterminate length of time," he said as the delegation departed. "Therefore (what we have decided) to do, which the air force is recommending, is to leave."
Mrs Clinton was not alone in having her plans disrupted by volcanoes this week. The continued eruption of Chile's Puyehue volcano, which has disrupted air travel from South America to Australia, forced a flight carrying Ban Ki-moon, the UN Secretary General, to divert to the northern Argentine city of Cordoba.
Mr Ban was forced to travel the remaining 400 miles to the capital Buenos Aires for a meeting with President Cristina Kirchner by car.
The 5,331ft Nabro volcano is close to Eritrea's border with Ethiopia and north of Djibouti, and has not erupted in at least 150 years.
It is located within the Danakil Depression, a junction of three tectonic plates spanning Eritrea and Ethiopia, whose spreading ridges could some 10 million years from now form a new ocean and split Africa in two.
Saturday, June 11, 2011
Volcano Watch: The Founding of the Hawaiian Volcano Observatory
Hawaii24/7.com: Volcano Watch: The Founding of the Hawaiian Volcano Observatory
(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)
(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)
As we approach the 100th anniversary of the Hawaiian Volcano Observatory (HVO), we have realized that, while 1912 has long been recognized as the year HVO was established, the actual founding date is not clear.
There was no ribbon-cutting ceremony or “grand opening” celebration to mark the occasion.
We know that HVO’s origin began in 1909 and that it was fully established by July 1912. But, the question of when HVO was actually founded remains. To answer it, we look back at when it all started.
In April 1909, Thomas A. Jaggar, Jr., was traveling to Japan to learn how its scientists monitor volcanoes. On the way, he stopped in Honolulu, where he delivered a speech on the need for careful and systematic study of volcanoes.
He said that “no better place could be found for it than … close to the crater of Kilauea.”
He also extolled the accomplishments of American scientist, Frank A. Perret, so successful at studying Italian volcanoes and forecasting their behavior that the Crown of Italy decorated him “for his splendid service to science and humanity.”
While in Honolulu, Jaggar spoke with Lorrin A. Thurston, who mentioned that establishing an observatory at Kilauea had been discussed locally for many years. Thurston and other local businessmen promised to raise money in support.
So, as early as April 1909, HVO’s founding was underway. It was a “twinkle in the eye,” but not yet a certainty.
Jaggar had difficulty getting the Massachusetts Institute of Technology (MIT) to allow the funds, set aside to establish an earth observatory in Massachusetts, to be spent in Hawaii. But by October 1910, he had found a way to purchase specialized equipment and have it shipped to Honolulu in anticipation of starting his work.
The “Jaggar plan” was in motion.
In January 1911, Frank Perret travelled from Italy to Boston, where he delivered lectures and met with Jaggar to discuss the latter’s “Hawaiian plan.” Jaggar had been trying (unsuccessfully) to get back to Hawaii since 1909 — He knew that a “demonstration” of his plans and intentions was needed to sustain the interest of his Honolulu supporters. Perret promised to go to Hawaii that summer (1911), even after Jaggar backed out.
Frank Perret, the most famous volcanologist of that time, arrived July 2, 191 at the edge of Kilauea caldera. During their first week, he began observing the lava lake within Halemaumau Crater, stretching a 1200-ft cable across the crater, and constructing a hut for observers and instruments at the eastern edge of the crater.
By the end of July, the temperature of molten lava was measured with sensors lowered from the cable – a first. The “Technology Station,” named after its sponsor, MIT, was completed, and immediately occupied. Perret had indeed set Jaggar’s vision in motion, but HVO had not yet been founded.
The date of Jaggar’s arrival kept slipping, and, eventually, Perret felt he had to return to his beloved Italy. So, unfortunately, the careful, continuous observations of Halemaumau activity, recorded by Perret, were interrupted for several months at the end of 1911.
Jaggar finally arrived Jan. 17, 1912 at the Volcano House hotel. That afternoon, he resumed observations and documentation of the active lava lake in Halemaumau. Thus began the continuous record of volcanic activity, which was one of Jaggar’s goals for an observatory.
Because that basis of the observatory was solidly established on this date, it is often cited as the founding of HVO.
But there is another interpretation on the start of HVO. John Dvorak, a former HVO staff scientist who has spent years researching Jaggar, reports HVO was founded when Jaggar received his first paycheck July 1, 1912.
Dvorak has written an excellent article on HVO’s beginnings, which can be accessed at http://ptonline.aip.org/journals/doc/PHTOAD-ft/vol_64/iss_5/32_1.shtml
No matter how one defines HVO’s founding, or what date is chosen, it’s clear that it occurred some time between July 2, 1911 (Perret’s arrival), and July 1, 1912 (Jaggar’s first paycheck).
HVO’s current staff will begin the celebration of the observatory’s 100th anniversary in January 2012 and continue it throughout the year. Information about events and activities will be posted in local newspapers and on the HVO Web site.
Stay tuned for an exciting centennial year.
Thursday, June 9, 2011
NASA Provides a Two-Satellite View and Video of the Chilean Volcano Eruption
Nasa.gov: NASA Provides a Two-Satellite View and Video of the Chilean Volcano Eruption
NASA's Aqua satellite and the GOES-13 satellite both captured their own unique views of the eruption of the Puyehue-Cordón Caulle volcano in Chile this week. One satellite provided a high-resolution image of the ash plume while the other provided a video showing the plumes movement over several days.
NASA's GOES Project released a satellite animation of the Puyehue-Cordón Caulle volcano that shows the movement of the ash plume over several days. The NASA GOES Project, located at NASA's Goddard Space Flight Center, Greenbelt, Md. created the animation from images obtained by the Geostationary Operational Environmental Satellite, GOES-13. The GOES series of satellites are operated by NOAA.
The GOES-13 animation includes visible and infrared imagery from GOES-13 that runs from June 4 at 1745 UTC (1:45 p.m. EDT) to June 6 at 1445 UTC (10:45 a.m. EDT). On June 4, the plume was blowing to the southeast. Through June 5 and 6, the winds shifted and viewers of the animation can see the plume start turning in a counterclockwise motion to the east, northeast and then north as high pressure moves in (In the south high pressure system winds rotate opposite they way they do in the northern hemisphere, so they shifted the winds from southeast to the north.
A visible image was taken on June 8 at 18:30 UTC (2:30 p.m. EDT) by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument that flies aboard NASA's Aqua satellite. The plume from the Puyehue-Cordón Caulle volcano in Chile has now expanded to the south and is now covering a much wider angle than earlier this week. The image shows the plume of ash now blowing to the east over Argentina in what almost appears to be a 90 degree triangle.
The MODIS Rapid Response Team is also located at NASA Goddard, and creates images from the MODIS instrument that flies aboard NASA's Aqua and Terra satellites.
According to MSNBC on June 8, flights in and out of Chile, Argentina and Buenos Aires, Brazil were suspended or delayed over the last several days and travelers should check with their airlines. The Associated Press and CBS News noted that the organization in Chile that monitors volcanic eruptions: the National Geology and Mines Service considers the eruption moderate so far, but it could change.
Meanwhile, satellite data from NASA and NOAA will help airlines determine the direction of the ash plumes and whether air travel can resume.
Tuesday, June 7, 2011
Chile's staggering volcanic spectacle
Salon.com: Chile's staggering volcanic spectacle
This morning's news that an estimated 42 million people were displaced by natural disasters in 2010 comes quick on the heels of a volcanic eruption in Chile that has caused 3,500 people to flee their homes.
According to AP, the eruption, which started on Saturday afternoon and continued throughout the day on Sunday, produced an ash cloud six miles high. No related injuries or deaths have been reported.
Ash from the Chilean volcano has blanketed a wide area -- including parts of Argentina -- and caused a Chilean-Argentinian border crossing to be temporarily closed. The Puyehue-Cordon Caulle chain of volcanoes, where the eruption took place, has lain dormant for more than 50 years.
Scroll down for astonishing images and raw footage of the eruption.
A column of smoke and volcanic lightning are seen over the Puyehue volcano [AP/Francisco Negroni, AgenciaUno]:
(You need to go to the original link to see these photos, but here's one:)
This morning's news that an estimated 42 million people were displaced by natural disasters in 2010 comes quick on the heels of a volcanic eruption in Chile that has caused 3,500 people to flee their homes.
According to AP, the eruption, which started on Saturday afternoon and continued throughout the day on Sunday, produced an ash cloud six miles high. No related injuries or deaths have been reported.
Ash from the Chilean volcano has blanketed a wide area -- including parts of Argentina -- and caused a Chilean-Argentinian border crossing to be temporarily closed. The Puyehue-Cordon Caulle chain of volcanoes, where the eruption took place, has lain dormant for more than 50 years.
Scroll down for astonishing images and raw footage of the eruption.
A column of smoke and volcanic lightning are seen over the Puyehue volcano [AP/Francisco Negroni, AgenciaUno]:
(You need to go to the original link to see these photos, but here's one:)
Friday, June 3, 2011
Why volcanoes are likely to continue to cause chaos in Europe
Blogs.reuters.com: Why volcanoes are likely to continue to cause chaos in Europe
By Dr Andy Hooper. The opinions expressed are his own.
Within the space of just over a year, aircraft have now been grounded in Europe twice by ash blowing in from Iceland. This has caused many millions of pounds of disruption.
A key question uppermost in many minds is whether the frequency of eruptions in Iceland is increasing. The short answer here is ‘yes, probably’. But, it is not just the frequency of eruptions that matters. To impact the airspace of the United Kingdom and continental Europe, the ash has to be ejected high enough, and be fine enough that it can remain airborne for days. Then the winds have to conspire to push it towards Europe, and the winds blow over Iceland from the north only a small fraction of the time.
Studies by researchers at the University of Iceland have noted that the frequency of eruptions from volcanoes beneath the Vatnajökull ice cap (including Grímsvötn, which erupted in May this year) seems to wax and wane with a cycle of about 140 years.
Prior to the 1980s, there were no such eruptions from these volcanoes for over 40 years and there have now been four within 15 years. The reason for the apparent cyclicity is not established but, in any case, we appear very likely to have entered a phase of more eruptions.
The volcanoes beneath the Vatnajökull ice cap are not, of course, the only ones in Iceland — Eyjafjallajökull, for instance, which erupted last year, is not covered by the Vatnajökull ice cap — and the same patterns may not apply elsewhere. However, perhaps more importantly than the number of eruptions, the University of Iceland study also noted that the intensity of eruptions increases in times of high activity, meaning that the height of the ash, and therefore the chances of it reaching Europe, also increases.
Perhaps of even greater concern is that the major fissure eruptions have also occurred during periods of high volcanic activity, although with only two of these within the last 800 years, this could be coincidence. Here the concern is not so much for air traffic, but for something far worse.
The Laki fissure eruption in 1783-1784 killed a quarter of the Icelandic population and led to the deaths of thousands throughout Europe, due to poisoning and extreme cold. In the twenty-first century, we might be able to mitigate the direct effects of poisoning somewhat, but the climatic effects would still be devastating for susceptible portions of the population and for agriculture.
On top of this pattern of variable eruption frequency, the ice caps in Iceland have been shrinking since the late nineteenth century. Vatnajökull, for instance, has lost an estimated 400 billion tonnes of ice over this time period. This has decreased the pressure on the hot mantle material beneath the crust, which feeds Icelandic eruptions, leading to increased magma generation.
As the last ice age ended, volcanism in Iceland was some 30 times higher than usual. The current rate of ice loss is now much less, but it is likely that on the order of two cubic kilometres of extra magma have been generated since the recent ice retreat began — equivalent to more than ten 2010 Eyjafjallajokull eruptions!
Perhaps our one saving grace, in the short term, at least, is that it may take quite some time for this extra magma to find its way to the surface. Trying to assess more fully the impact of the melting ice on future eruptions is something that colleagues and I continue to work on.
Dr Andy Hooper is a geophysicist at Delft University of Technology and is an expert on volcano deformation.
Mexican volcano rumbles
Xomjianet.com: Mexican volcano rumbles
MEXICO CITY, June 3 (Xinhua) -- Mexico's tallest volcano released a column of ash that reached three kilometers in height, but the prospect of an eruption remains remote, Mexican civil protection officials said.
The Popocatepetl Volcano, located approximately 70 kilometers southeast of Mexico City, has made five exhalations since 11 a.m. on Thursday, releasing columns of steam and ash. The ash was expected to fall onto the city of Puebla.
Civil protection officials have maintained the same alert level for the 5,426-meter Popocatepetl, urging people to stay away from the crater.
Popocatepetl, the second-tallest peak in Mexico, poses no risk to nearby Mexico City, although some smaller communities near the volcano have been evacuated in recent years.
MEXICO CITY, June 3 (Xinhua) -- Mexico's tallest volcano released a column of ash that reached three kilometers in height, but the prospect of an eruption remains remote, Mexican civil protection officials said.
The Popocatepetl Volcano, located approximately 70 kilometers southeast of Mexico City, has made five exhalations since 11 a.m. on Thursday, releasing columns of steam and ash. The ash was expected to fall onto the city of Puebla.
Civil protection officials have maintained the same alert level for the 5,426-meter Popocatepetl, urging people to stay away from the crater.
Popocatepetl, the second-tallest peak in Mexico, poses no risk to nearby Mexico City, although some smaller communities near the volcano have been evacuated in recent years.
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