Rf - Volcano Case Study

EARTHQUAKE CASE STUDY – MOUNT PINATUBO, 1991 ERUPTION

Before •Part of Kambales Mountain Range • approximately 7 million years old ◦active for 1.1 million ◦dormant for 450 years •holy place for people of Indonesia •7.8 Magnitude Earthquake in the Pinatubo region in July 1990 •USGS begins monitoring Mount Pinatubo •Rising amount of Magma in underneath the Earth causes minor earthquakes ◦Increased amount of Steam coming to the surface •March: Scientists begin to look for signs of Volcanic activity ◦Sulphur Dioxide released to the surface •Many small Earthquakes occur •June 5th – Level 3 alert issued (see below) •June 9th 1991 – Ash Eruptions •June 10th – Level 5 alert issued, US evacuates Marines and USGS center ◦Small(in comparison) Pyroclastic flows occur ▪Most flow into the local river stystem

Historical eruption zones vs Preparedness zones

Its important to note in the above two diagrams the differences between ancient rock deposits and the newer preparedness zones. The entire area is covered in some kind of volcanic rock (which makes sense when one considers the historical origins of the Island – created by a hotspot under the earths crust.), but one side of the volcano has much more rock deposited by old lahars and pyroclastic flows, as well as lava flows. It is interesting to note that this was not taken into consideration when the preparedness map was created. The Areas north of Angeles city are included in level 3, but yet the ground seems to include rock deposits from pyroclastic flows, which are the fastest moving of all the volcanic hazards. During •June 12th – considered to be the first of the eruptions, more significant than the 9th, but not as powerful as the following ones ◦Much ash and steam ejected, most of it finds its way into the river system •June 13th – more ash eruptions •June 14th ash Column approx. 25 Km stretches Into the air. Pyroclastic flows reach approx. 15 km from the source •June 15th – major explosion. Considered to be the second biggest that century and the largest in a densely populated area. Magma flowed out of the mountain when the Caldera blew. ◦Ash column extends to be about 35 Km up ▪Coincides with a cyclone, which although common to the region, blew the ash in many directions further away from the source. As well, the ash particles mixed with the water particles and actually rained down in some areas. ◦Pyroclastic flows fill some valleys, rivers ◦lahars flow out into the surrounding Luzon valley region. •USGS continues to provide information about the Volcano and the dangers associated with it •Early detection system is proven to be a success. •Approx 800 people killed ◦approx 1.18 million affected ◦Local Aeta people displaced from the slopes of the mountain ▪warned by early detection system ◦some 5000 people saved by early evacuation •approx 500 Million dollars in property damage ◦approx 250 million saved ◦destroyed approx 5000 homes and damaged approx 70000 •the ash from Pinatubo was so great that it affected global temperatures, lowering them by approx 0.5 Celsius

Top Left – Ash Column from Mount Pinatubo Mid Left – Ash fall caused by the rain from Mount Pinatubo Bottom left – Aircraft hangars destroyed by the falling ash Right – Before (A) and After(B) pictures of a valley filled by a pyrocalstic flow

Top – map showing extent of lahars/pyrocalstic flows Right – pictures showing damage of lahars and pyroclastic flows Bottom – map showing the time delay in the travel of the ash cloud.

After •Many Aetan people still awaiting to return home in massive resettlement camps •Philippine government has new emergency preparedness plan •Large amounts of Ash in many valleys ◦Some parts still as hot as 500 Celsius ◦water sometimes becomes super heated •many farms covered in sediments left by lahars ◦influx of people to Angeles city in search of work