Lascar Volcano, Chile
Volcano Lascar (23.32 S, 67.44 W), is the most active volcano in the central Andes and is characterised by persistent fumarolic activity, occasional vulcanian and steam eruptions.
Volcano Lascar was formed by subduction. Subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's crust, as the plates converge. Both the South American and the Nazca plate were involved in the forming of Volcano Lascar.
Since 1984, there have been four cycles of lava dome building within the summit crater, dome subsidence, and vulcanian to plinian eruptions. These culminated in the largest historic eruption of Lascar on April 19 and 20, 1993, which sent ash to the SE as far as Buenos Aires. The eruption lasted for two days. The highest intensity pulse occurred on the second day, forming a 23-km-high column above the volcano that dispersed a blanket of coarse pumice to the southeast and generated the most energetic pyroclastic flows, which extended 8.5 km NW of the summit.
The government declared the disaster zone as an 'open city' area to encourage aid from external groups. Power and water supply were cut off within the danger zone to further discourage residents from returning. The Commission on Human Rights allowed the use of emergency measures and gave clearance to forcibly evacuate residents who refused to leave.
The most effective method of detecting unrest at volcanoes is seismic (earthquake) monitoring. Direct visual observations are also important in confirming volcanic eruptions. They allow scientists to calibrate seismic data to remotely interpret volcanic activity. KVERT scientists have developed methods of estimating eruption plume height from the intensity of seismicity. Analysis of satellite imagery is also another powerful technique used to detect volcanic eruptions and track the movements of ash clouds.
Bibliography:
http://en.wikipedia.org/wiki/Lascar_Volcano, extracted 22-02-2010
http://geohazards.buffalo.edu/documents/Erosion.pdf, extracted 22-02-2010
