I have been watching the eruption of Mt ChaitÃ©n in Chile, South America very closely for the last few weeks. It appears as if it may produce a major eruption soon. The last known eruption was in 7420 BC Â± 75. The progress of the 2008 eruption has been as follows.
April 30: A significant earthquake preceded the first explosions;
May 2: More earthquakes arrayed radially around the caldera implying a very large magma chamber;
May 15: Near steady-state explosive eruptions (Plinian) releasing about two cubic kilometers of ejecta of 4-5km in altitude.
Eruptions are rated by the Volcanic Explosivity Index (VEI). The following are examples of recent eruptions and their VEI.
VEI=5 Plinian, ejecta > 1 kmÂ³, e.g. St. Helens (1980)
VEI=6 Plinian/Ultra-Plinian, ejects > 10 kmÂ³, e.g. Mount Pinatubo (1991)
VEI=7 Plinian/Ultra-Plinian, ejecta > 100 kmÂ³, e.g. Tambora (1815)
VEI=8 Ultra-Plinian, ejecta > 1,000 kmÂ³, e.g. Toba (73,000 BP)
Mt ChaitÃ©n eruptions have ejected around 2 kmÂ³ of ash, giving it a solid VEI=5 on a par with Mt. St. Helens.
Mt ChaitÃ©n eruptions are not yet of sufficient energy to reach the 10km to the stratosphere (Ultra-Plinian), needed to affect weather on the global scale, although emissions reached an altitude of 8 km on the 12th May.
Some of the stunning lighning images being taken of the Mt ChaitÃ©n eruption.
The initial fuselage of shallow focus earthquakes (10 km depth), larger than magnitude 4, delineate a potentially very large magma chamber, accompanied the start of the Plinian phase on May 2.
4.4 April 30, 2008 at 11:52 PM 17km E 5.3 May 02, 2008 at 01:51 AM 30km NE 4.9 May 02, 2008 at 07:13 AM 13km NW 4.1 May 02, 2008 at 06:13 PM 16km SW 5.0 May 02, 2008 at 10:36 PM 30 km NE
Note the epicenters arrayed radially around the caldera. Their locations imply a very large magma chamber might be released.
Today the Volcanism blog reports changes in seismic activity indicating fragmentation and instability around the volcanoâ€™s central conduit and beneath the lava dome. The volcano may go ultra-plinian if the magma conduit breaks up, and the capping lava dome explodes away. The consequences of large-scale injections of ash and gases into the stratosphere are disruptions of global climate, particularly initial cooling for a few years, depending on the amount of material released. A Mt Tambora scale eruption would cause enough disruption of normal climate to cause widespread crop losses.
Below are some resources that I will update over the next few days.
Volcanism blog.– Latest reports from Chile
Satelite Image – of cloud-top height
Volcano Live – Reports by Jon Seach