Pinatubo Effects Question | Back |

The local impacts of the 15th June 1991 eruption around Mount Pinatubo, Luzon, Phillippines (www.vulkaner.no/v/volcan/pinatubo/pinatub1.html ).

Adapted WJEC question… January 2005

a)    With reference to (resource 1 – the map above) explain two ways in which high intensity tectonic events do not always lead to large scale impacts.                                                                                                  4)

b)   Use examples to explain the causes of, and hazards associated with, two of the following:

         Tsunami;               lahars;      ground shaking;

         Ash fall;                Landslides;        pyroclastic flows;                           8)

c) Use a located example to discuss the effectiveness of strategies used to overcome the impacts of tectonic activity.       KI4    [see below]                    8)

 

Contrasting effects of ash loading on buildings, 1991 eruption of Mount Pinatubo, Philippines

 

 

Ashfall from the 15 June 1991 eruption of Mount Pinatubo resulted in the accumulation of  5-10 cm of wet ash in the area of former U.S. Clark Air Base, located 20 km northeast of the volcano. Densities of ash samples collected here ranged from 1,200 to 1,600 kg/m3 (dry) and 1,500 to 2,000 kg/m3 (wet).

A survey of damaged buildings in Castillejos, 27 km southwest of Mount Pinatubo identified the roof structure as the most significant indicator of damage in a comparison of residential and nonresidential buildings. Sixteen percent of surveyed buildings with short-span roofs suffered major damage, with 43 percent having no significant damage. Seventy-five percent of buildings with long-span roofs (greater than 5 m clear span) were severely damaged, and only 17 percent were without significant damage (Spence and others, 1996, p. 1059).

 
In the Philippines, 21 volcanoes are considered to be still active, having erupted within the last 600 years. In the twentieth century, eleven volcanoes recorded sixty-three eruptions. The eruptions of Mt. Pinatubo in Central Luzon, during the period 12-15 June 1991, and the subsequent effects of typhoons, heavy rainfall and lava flows resulted in extensive damage to public infrastructure and private property (see box 5). In early November 1993, Mt. Pinatubo erupted again killing 11 villagers. In minutes, 90 per cent of the 400 houses of a nearby village had disappeared. The eruption dumped billions of tons of rocks and ash on Pinatubo's slopes. As heavy rains came, those deposits turned into ferocious rivers of mud that could wipe out everything in their path. Furthermore, lava flows from Mt. Pinatubo continued to claim lives and destroy property and infrastructure.