California and Philippines

Question 1

Hazards in the Philippines?

Answer 1

It sits across a major plate boundary, the Philippine and Eurasian tectonic plates, so it faces significant risks from volcanoes and earthquakes.
The Eurasian plate is forced beneath the Phillipine, creating the deep Manila Ocean Trench, to the west.
Its northern and eastern coasts face the Pacific, the world’s most tsunami-prone ocean.
It lies within South-East Asia’s major typhoon belts. In most years, it is affected by 15 typhoons and struck by 5 or 6 of them.
Landslides are common in mountain districts.

Question 2

Mount Pinatubo’s volcanic eruption in June 1991.

Answer 2

Mount Pinatubo’s eruption was the biggest the world had seen for over 50 years. The volcano showed signs of eruption in April 1991, with steam explosions and minor earthquakes.
By 9 June 1991, 58,000 people had been evacuated, reaching 200 000 by 12 June when the first eruption sent a cloud of ash 20 km into the atmosphere, spreading over South-East Asia. The second eruption on 15 June was cataclysmic; a dome on the side of the volcano collapsed, creating a pyroclastic blast and causing huge lahars. However, effective monitoring and management reduced Pinatubo’s death and injury toll to just over 4300 people.

Question 3

Some hazard risks in the Philippines are complex because they have multiple effects. One earthquake in 2006:

Answer 3

• killed 15 people, injured 100 and damaged or destroyed 800 buildings
• generated a local tsunami 3 metres high
• triggered landslides which breached the crater wall of Parker Volcano, and then fell into Maughan Lake…
• …creating a flood which washed away houses.

Question 4

Physical causes of the Guinsaugon landslide

Answer 4

There was unseasonable torrential rain; 2000mm of rain fell in 10 days in February- normally the dry season.
La Nina- a cyclic ocean and wind current affecting South-East Asia- was probably the cause of the rainfall
A 2.6 magnitude earthquake struck just before the slide and may have triggered it.

Question 5

Human causes of the Guinsaugon landslide

Answer 5

Deforestation of native forest cover protecting the soil. In 50 years, logging has reduced several million hectares of forest to about 600 000 today.
Replacement of native forest by shallow rooted trees, such as coconuts, further reducing soil protection.

Question 6

Hazards in California

Answer 6

San Francisco lies along the San Andreas fault, where the Pacific Plate moves north-westwards past the North American Plate. The two move in the same direction but the Pacific Plate moves more quickly, thus creating friction.
In 1906, San Francisco was destroyed in an earthquake measuring 8.2 on the Richter Scale. It fractured gas pipes (which caused explosions and fires) and water mains (which could have prevented fire spread). A further earthquake, of magnitude 7.1, occurred in 1989. With its epicentre at Loma Prieta. It caused major damage and deaths- some buildings collapsed/ were damaged. Five years later a further earthquake shook Northridge in LA.