Mount Pinatubo Phillippines 1991 Background It was heavily

Mount Pinatubo Phillippines, 1991

Background • It was heavily eroded and had never erupted in recorded history, until June 15 th 1991 • Mount Pinatubo is a Strato volcano • It lies on the boundary between the Philippines plate and the Pacific plate • Major Eruption 500, 3000, 5000 years ago • The second biggest eruption of the century • Approximately 30, 000 people lived on the flanks of the volcano

Causes • In 1990 there was a magnitude 7. 8 earthquake 100 kilometres (62 miles) northeast of the Pinatubo region. • This was a result of the reawakening of Mount Pinatubo. • Starting from April 2 nd 1991 small amounts of ash began to be projected into the atmosphere • For the next two months, tremors were recorded within the volcano • Just days before the major eruption up to 2, 000 earthquakes a day were recorded • This suggests the magma was near the surface • From early June ash and gas was constantly coming out of the volcano • At approximately 8: 52 am three explosions sent a mushroom cloud 20 km into the sky

Was it Predicted? • The USGS and volcanologists monitored the volcano weeks before the eruptions • They began to notice that tremors were gradually becoming larger and more frequent • All the signs point towards a volcanic eruption • However the scientists were faced with a problem • If they said it was going to erupt at a certain point and it erupted before, then thousands of people could have died • On the other hand, predict it too early and people that have been evacuated may start to come back to their villages and agricultural land, then if it erupted thousands may have died

Predicting the eruption • Three successful evacuations were put in place, first they evacuated everything within 10 km of the summit, this increased to 20 km, then 40 km. • The 10 km and 10– 20 km zones had a total population of about 40, 000, while some 331, 000 people lived in the 20– 40 km zone. • Five stages of alert were defined, from level 1 (low level seismic disturbances) up to level 5 (major eruption in progress). Daily alerts were issued • This prevented many people being killed by the eruption and its effects

Immediate Effect • A huge pyroclastic flow was triggered • The ice cap at the summit melted and mudflows charged down the volcano • Travelling at over 100 km/h the dust and hot ash buried nearby villages • Ten cubic kilometres of material were launched into the upper atmosphere • The summit was replaced by a caldera 2. 5 km wide • The height of the summit decreased by 260 m

Effects • Huge amounts of ash began to settle in nearby areas • Typhoon Yunya then shortly followed and this ash became heavy when wet • This caused poor quality houses to collapse and the death toll to rise • This caused most of the 800 deaths recorded

Effects • 800 square kilometres (200, 000 acres) of rice-growing farmland destroyed, and almost 800, 000 head of livestock and poultry killed, destroying the livelihoods of thousands of farmers • 20 million tons of SO 2 being ejected meant that global temperatures fell by around 0. 5 degrees C • 1. 2 million people affected • Schools and transport lines destroyed • Jobs lost • The eruption was ten times larger than the 1980 eruption of Mount St. Helens

Nevado Del Ruiz Colombia, 1985

Background • 3: 06 pm, on November 13, 1985, Nevado Del Ruiz erupted • Second largest volcanorelated disaster of 20 th Century • Nevado Del Ruiz is a Strato Volcano • It lies on the Andes mountain range and on the edge of the Pacific Ring of Fire • It is also on the boundary where the Nazca plate is subducting below the South American plate

Causes • Nov. 1984 signs of small earthquakes • Steam and gas were detected near the summit • Sept 11, 1985 large ejection of ash from the peak of the volcano • Nov 10, 1985 signs of magma movement and tremors • An Italian volcanological mission analyzed gas samples. • They reported the risk of lahars to be very high

Was it Predicted? • Clear signs of an Active Volcano • There was no evacuation • Authorities would not take costly preventative measures to evacuate • Last eruption over 140 years ago • People thought there was no danger • Armero's mayor reassured city after an ash eruption • On the afternoon of November 13, Nevado Del Ruiz erupted

Effects • Lahar produced • Land flow or land slide, composed of pyroclastic material and water • Caused by a small eruption • Deadliest lahar in recorded history • Pyroclastic flow melted the ice cap that set off the lahar at 60 km/h • The nearby town of Armero was completely destroyed

Effects on Armero (nearby town) • At the time Armero's population was 28, 700 • Over 23, 000 were killed • 5, 000 were injured • 5, 000 homes destroyed • All jobs and agricultural land lost

Effects • The estimated cost of the disaster is $1, 000, 000 • Total mass ejected: 35 million tons • Over 23, 000 deaths

“Scientists later looked back to the hours before the eruption and noticed that several long-period earthquakes, which start out strong and then slowly die out, had occurred in the final hours before the eruption. Volcanologist Bernard Chouet said that, "the volcano was screaming 'I'm about to explode'", but the scientists who were studying the volcano at the time of the eruption were not able to read this signal. ”