Here we present a selection of satellite data showing ash clouds produced by the May 2008 eruption of Chaitén volcano, Chile. The eruption produced sustained ash emissions and several stratospheric ash plumes that deposited ash over southern Chile and Argentina. For background information see the following article: S.A. Carn, J.S. Pallister, L. Lara, J. Ewert, S. Watt, A.J. Prata, R.J. Thomas, G. Villarosa (2009). The unexpected awakening of Chaitén volcano, Chile. EOS Trans. AGU, 90(24), 205-206.
Below we provide links to online GOES satellite images loops showing eruptions of Chaitén on 6 and 8 May 2008. Many thanks to Dan Lindsey and Bernie Connell (NOAA CIRA) and Mike Fromm (NRL) for these loops.
GOES loops of the 6 May eruption (these show deposition of ash from the trailing edge of the 6 May eruption cloud as it drifts over Argentina):
Ch2 (3.9 µm): http://rammb.cira.colostate.edu/projects/pyrocu/chile_volcano/ch2loop.asp
Ch4 (11 µm): http://rammb.cira.colostate.edu/projects/pyrocu/chile_volcano/ch4loop.asp
GOES loops of 8 May eruption:
3.9 µm: http://rammb.cira.colostate.edu/projects/pyrocu/chile_volcano_may8/ch2loop.asp
11 µm: http://rammb.cira.colostate.edu/projects/pyrocu/chile_volcano_may8/ch4loop.asp
11-12 µm: http://rammb.cira.colostate.edu/projects/pyrocu/chile_volcano_may8/lwdiffloop.asp
MODIS visible imagery of Chaitén ash plumes
A selection of visible images from the Terra and Aqua MODIS sensors showing ash plumes from Chaitén over Chile and Argentina. Images are courtesy of the MODIS Rapid Response Project at NASA/GSFC (http://rapidfire.sci.gsfc.nasa.gov/).
May 2, 13:50UT: Chile.A2008123.1350.1km.jpg
May 3, 14:35UT: Chile.A2008124.1435.1km.jpg
May 5, 14:25UT: Chile.A2008126.1425.1km.jpg
May 5, 18:35UT: Chile.A2008126.1835.1km.jpg
May 6, 19:15UT: Chile.A2008127.1915.1km.jpg
May 9, 18:10UT: Chile.A2008130.1810.2km.jpg
MODIS ash mass retrievals
Dr Fred Prata, Norwegian Institute for Air Research, Norway
Email: firstname.lastname@example.orgThe total mass, mass loading, particle size and (infrared) optical depth of fine ash (particles with radii < 10 µm) from the eruption of Chaitén volcano, Chile, is retrieved using the infrared channels of the Terra and Aqua MODIS instruments. The retrieval relies on brightness temperature measurements at 11 and 12 µm (MODIS channels 31 and 32) and utilizes a microphysical model of volcanic ash and the discrete ordinates method for radiative transfer calculations. Volcanic ash contains large amounts of silicates that scatter and absorb infrared radiation differently to meteorological water and ice clouds. By coupling a microphysical model of the ash (e.g. refractive indices, particle size distribution) to a radiative transfer model, the infrared optical depth and effective particle size can be retrieved from two infrared MODIS measurements on a pixel-by-pixel basis. Since the method relies on infrared radiation, the technique works equally well during the day or night.
The results shown provide 4 views from two satellites each day for the Chaitén ash plume on 3 and 5 May, 2008. Mass loadings are determined from the particle size and infrared optical depth by assuming a plume of 2 km thickness and integrating over the size distribution. The total mass is determined by summing the masses in each pixel over the entire image.
Fine ash is hazardous to jet aircraft and can remain in the atmosphere for many hours as it is transported by the winds. The ash can be tracked and identified using the 11 and 12 µm MODIS channels and areas with high densities of ash delineated as hazardous. Ashfall can also cause damage to infrastructure (buildings and roads), disrupt power and contaminate water supplies. Respirable (fine) ash is a hazard to humans, causing breathing difficulties, eye irritation and is a risk to people with asthma. In the thickest parts of the plume, mass loadings can be very high, sometimes exceeding 50 mg m-3. Even several hundred kilometres downstream from the volcano fine ash mass loadings are significant and high enough to cause damage to jet aircraft engines. The Chaitén ash travelled as far as South Africa and at least one aircraft encounter has been reported.
Further information can be found in:
Baxter, P.J., 1999, Impacts of eruptions on human health: In H. Siggurdson (ed.), Encyclopaedia of Volcanoes, Academic Press, New York, p.1035-1043.
Prata, A. J., 1989, Radiative transfer calculations for volcanic ash clouds, Geophys. Res. Lett., 16, 1293 – 1296.Prata, A. J., 2008, Satellite detection of hazardous volcanic clouds and the risk to global air traffic, Natural Hazards, doi:10.1007/s11069-008-9273-z (in press).
Prata, A. J. and Grant, I. F., 2001, Retrieval of microphysical and morphological properties of volcanic ash plumes from satellite data: Application to Mt. Ruapehu, New Zealand., Quart. J. Roy. Meteorol. Soc., 127(576B), 2153--2179, doi:
Wen, S. and Rose, W.I., 1994, Retrieval of sizes and total masses of particles in volcanic clouds using AVHRR channels 4 and 5, J. Geophys. Res., 99(D3), 5421 – 5431.
Images showing retrievals of ash concentration (in mg m-3) in the Chaitén ash plumes:
CALIPSO dataThese images show data from the CALIOP lidar instrument aboard the CALIPSO satellite, taken at ~4:30 UT on 7 May. The left image shows lidar backscatter at 532 nm, and the right image shows the depolarization ratio (which is an indication of the shape and phase of aerosol particles). The prominent feature extending from ~5-16 km altitude in the top image is the drifting volcanic cloud produced by the 6 May 2008 eruption of Chaitén. The moderate depolarization measured in this cloud (lower image) indicates that the particles are likely solid, perhaps volcanic ash or ice. The persistence of this signal in the CALIPSO data suggests small particle sizes.