Ash and pumice particles were lofted high into the atmosphere after an explosive eruption of Chile's Calbuco volcano on April 22, 2015 and the debris has been darkening skies and burying parts of Chile, Argentina, and South America for nearly a week. Along with 210 million cubic meters of ash and rock, the volcano has been spewing sulfur dioxide (SO2) and other gases.
Near the land surface, sulfur dioxide is a acrid-smelling gas that can cause respiratory problems in humans and animals, but when it is higher in the atmosphere, it can have an effect on climate. When SO2 reacts with water vapor, it creates sulfate aerosols that can linger for months or years. Those small particles can have a cooling effect by reflecting incoming sunlight, NASA's Earth Observatory writes.
Image credit: NASA Aura/OMI. Acquired: April 23 – 26, 2015.
The images above show the average concentration of sulfur dioxide over South America and surrounding waters from April 23 to 26, 2015. The maps were made with data from the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite. Like ozone, atmospheric sulfur dioxide is sometimes measured in Dobson Units. If you could compress all the sulfur dioxide in a column of atmosphere into a single layer at the Earth’s surface at 0 degrees Celsius, one Dobson Unit would be 0.01 millimeters thick and would contain 0.0285 grams of sulfur dioxide per square meter.
On the maps above, data appear in stripes or swaths, revealing the areas observed (colored) or not observed (clear) by Aura on a given day. Note how the plume moves north and east with the winds.
By April 28, the plume of SO2 had reached the Indian Ocean, as visible in this 7-day movie by GNOME-2.
Image credit: The Global Ozone Monitoring Experiment-2 (GOME-2) onboard MetOp-A and MetOp-B.(via SpaceWeather)
So far, Calbuco has released an estimated 0.3 to 0.4 teragrams (0.3 to 0.4 million tons) of SO2 into the atmosphere. The gas was injected into the stratosphere (as high as 21 kilometers), where it will last much longer and travel much farther than if released closer to the surface. The SO2 will gradually convert to sulfate aerosol particles. However, it is not clear yet if there will be a cooling effect from this event.
The SO2 total is much lower than the recent Holuhraun eruption, which released about 11–12 teragrams, or 30 to 40 times more than Calbuco. “But the SO2 from Holuhraun was emitted over several months and was mostly confined to the lower troposphere, limiting its climate impacts,” said Simon Carn, a part of the OMI team and professor at the Michigan Technological University. “In terms of climate impacts, Calbuco is probably more significant due to the stratospheric SO2 injection.” (EO)
The natural color image below, acquired on April 25 by the Advanced Land Imager on NASA’s Earth Observing-1 satellite, shows Calbuco’s plume rising above the cloud deck over Chile.
Image credit: NASA EO-1/ALI. Acquired: April 25, 2015.
Another interesting feature of SO2 in the atmosphere is an impressive display of bright exotic colors in the evening twilight sky. Helio C. Vital took the following image from Rio de Janeiro, Brazil on April 26th:
Taken by Helio C. Vital on April 26, 2015 @ Rio de Janeiro, Brazil (via SpaceWeather)
Many of Vital's photos show a distinctly purple hue, one of the telltale signs of a volcanic sunset. Fine volcanic aerosols in the stratosphere scatter blue light which, when mixed with ordinary sunset red, produces a violet hue, SpaceWeather's Tony Phillips explains.
"But purple isn't the only thing to look for, says atmospheric optics expert Les Cowley. In addition, he advises, sky watchers should be alert for a very bright yellow twilight arch, fine cloud structure in the arch seen through binoculars, and long diffuse rays and shadows."
Featured image credit: NASA EO-1/ALI
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