How are people affected by a

Volcano eruption?

In 1990 the US Geological Survey claimed that there were 540 active volcanoes in the world. Three-quarters of those were in the Pacific Ring of Fire. The list did not include a little known volcano in the Philippines which had not erupted since 1380. On 9June 1991, Mount Pinatubo hit the headlines. It became one of the three largest eruptions in the world in the 20th century.

The Philippines lie on a destructive plate margin. The Philippines Plate, composed of oceanic crust, moves north-westwards towards the Eurasian Plate, which is continental crust. Where they meet, the Philippines Plate is forced to dip steeply down under the Eurasian Plate. The oceanic crust is turned into magma, rises, and erupts on the surface. The Philippines owe their existence to the almost constant ejection of lava over a period of several million years. Even before Pinatubo erupted, there were over 30 active volcanoes spread across the country’s many islands.

Fortunately there were several advance warnings of a possible eruption. On 7 June the Americans evacuated all 15,000 personnel from their nearby airbase, From 9 June there were many eruptions, but none matched that of 12 June. An explosion sent a cloud of steam and ash 30km into the sky. As the ash fell back to earth, it turned day into night. Up to 50cm of ash fell on nearby farmland, villages and towns. Over 10cm fell within a 600km radius, and some even reached as far away as Australia. The eruptions continued for several days. They were accompanied by earthquakes and torrential rain – except that the rain fell as thick mud. The weight of the ash caused buildings to collapse, including 200,000 homes, a local hospital, most of the schools and many factories. Power supplies were cut off for three weeks and water supplies were contaminated. Roads became unusable and bridges were destroyed making relief operations even more difficult.

The area surrounding Mount Pinatubo was excellent for rice growing. The thick fall of ash, however, ruined the harvest in 1991, and made planting for 1992 impossible. Over one million farm animals died, either through starvation (no grass to eat) or from drinking contaminated water. Hundreds of farmers and their families were forced to move to cities to seek shelter and food. Huge shanty-type refugee camps were set up. Disease spread rapidly, especially malaria, chicken-pox and diarrhoea. Within a few days the monsoon rains started. Normally these rains are welcomed as they bring water for the rice crop. In 1991, and again in 1993, they were so heavy that they caused flooding and lahars (mud flows). Lahars form when heavy rain flows over, and picks up, large amounts of volcanic ash. Lahars and landslides covered many low-lying areas in thick mud. Finally, ash ejected into the atmosphere encircled the earth within a few days. It blocked out some of the sun’s heat for several months, and lowered world temperatures. Scientists believe the eruption may delay global warming by several years. The eruption and after effects caused the deaths of about 700 people. Only six died as a direct result of the initial eruption. Over 600 died later through disease, and another 70 were suffocated by lahars.

► Answer the questions.

1. Why did so many people live on the slopes of Mount Pinatubo in June 1991?

2. Do you believe that eruptions can be a considerable hazard to human activity and, sometimes, to human life?

3. What caused the eruption of Mount Pinatubo?

4. Is it true that the most violent volcanic eruptions occur at destructive plate margins?

5. List the: a) immediate effects

b) long-term effects of the eruption of Mount Pinatubo.

10. Read the text The Great Forests and say whether the statements after it true (T) or false (F).