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close this bookBasic Concepts in Environment, Agriculture and Natural Resources Management: An Information Kit (IIRR, 1993, 151 p.)
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View the documentNatural hazards

Natural hazards

Natural hazards

Natural hazards become disasters when the disruptions exceed the adjustment capacity of a community. This section describes three major natural disasters encountered in the Philippines: earthquakes, volcanoes and typhoons.


The earthquake that struck Luzon Island last July 16, 1990, at 4:16 p.m. was due to a break in the solid layer of the earth. The biggest shock was felt at Nueva Ecija, Tarlac, Pangasinan, Baguio, La Union and part of Nueva Viscaya. The Office of Civil Defense, Department of National Defense, estimated that about 1,666 people were killed and some 3,561 injured. Most injuries were sustained by people who were hit by falling objects. Many deaths occurred during escape.


Three things are emitted from volcanoes: projectiles, ashfall and lava or lahar. Projectiles can destroy infrastructure and harm people depending on the speed and size of the projectile. Ashfall has always been a source of anxiety among evacuees although the negative effects on health have generally been exaggerated. Residents nearer the eruption are actually more vulnerable to projectiles while those further away are more affected by finer ashfall materials which could enter the respiratory tract, potentially causing lung diseases. Injuries indirectly caused by ashfall occur when heavily-laden roof-tops collapse after a heavy rain. The effects of lava (molten rock) or lahar (volcanic mudflow) are almost similar. Both destroy communities by the property of mass impact or by blocking river channels, then causing flash floods. Lava has the property of intense heat and burns anything alone its path.

Tropical cyclones: depression, storms and typhoons

The impact of these calamities are due to their wind velocity or their potential to cause floods. For example, the destructive effect from wind was the main impact of Typhoon Ruping in 1990. On the other hand, the thousands of people killed in Ormoc City, Leyte, in 1991 was due to a flash flood brought about by a tropical storm. An average of 19 tropical cyclones enter the Philippine area of responsibility though only a small percentage of these are classified as destructive. The most common cause of injury during these calamities is drowning.

Frequency of tropical cyclone passage over each geographical zone in the Philippines.