CASE STUDY OF A VOLCANIC ERUPTION & AN EARTHQUAKE

(Spring 1980: On 20 March there was a minor earthquake, which measured 4.1 on the Richter scale. There were many more tremors over the next few days until, on 27 March, there was a small eruption of steam and ash. Minor eruptions occurred daily, attracting fin increasing number of tourists. By early May, the north side of the mountain began bulging by 1.5m a day, indicating a build-up of magma and an increase in pressure. This reached a peak on the morning of 18 May. On 18 May, at 08:32 an earthquake (magnitude 5 on the Richter scale) caused the bulge to move forwards and downwards. The released material formed a landslide of rock, glacier ice and soil. This raced downhill to fill in Spirit Lake and then, reinforced by the water displaced from this lake, moved rapidly down the northern fork of the Toutle Valley. The mudflow reached Baker Camp, but floodwater continued down the valley and sediment blocked the port of Portland On the Columbia River. At 08:30, the exposed magma exploded sideways sending out blast waves of volcanic gas, steam and dust (called a nuée ardente) which moved northwards for 25km. Within this range, every form of life - plant and animal - was destroyed. In the rest of morning, a series of eruptions ejected gas, ash and volcanic 'bombs' (rocks). The thicker ash rose 20km and drifted eastwards before settling. Inhabitants at Yakima, 120km away, could only go out if they wore facemasks. Three days later, the volcanic 'plume' (cloud) of fire ash reached the east coast of the USA. Several days later, the ash had completely, encircled the world.)

CASE STUDY OF AN EARTHQUAKE TREMOR: Kobe, Japan.

• Kobe is a on a minor fault, the Nojima Fault, which lies above a destructive plate margin. Here the Philippine Plate (oceanic crust) is forced downwards on contact with the Eurasian Plate (continental crust).
• The earthquake occurred at 05:46 of 17 January 1995. It recorded 7.2 on the Richer scale and lasted for 20 seconds. During this time, the ground moved 18cm horizontally and 12cm vertically. The widespread devastation was due to the earthquake’s focus being so near to the surface and its epicentre being so close to Kobe.
• Nearly 200.000.buildings collapsed, and also a 1km stretch of the elevated Hanshin Expressway and numerous bridges along a 130 km section of the bullet train route. Several trains on minor lines were derailed.
• 120 of the 150 quays in the port of Kobe were destroyed.
• Electricity, gas and water supplies were disrupted.
• Fires, caused by broken gas pipes and ruptured electricity mains, raged for several days, destroying a further 7500 houses (many of which were made of wood). At one time, the wall of fire extended for over 400 metres.
• Roads were at gridlock, delaying ambulances and fire-engines.
• An estimated 230 000 people were made homeless and had to live in temporary shelters (unheated school gyms or in open parks) at a time when night-time temperatures dropped to -2°C. There was a short-term shortage of blankets, clean water and food.
• People were afraid to return home as the 716 recorded aftershocks lasted several days after the main event (74 were strong enough to be felt by humans).
• Industries, including Mitsubishi and Panasonic, were forced to close.
• Final figure put the death toll at 5500, injuries at 40000 and houses totally destroyed at 180000. However, the newly opened Kansai International Airport and Akashi Bridge were presumably due to their high-tech at withstanding earthquakes.
• Kobe's infrastructure, including water, electricity, services, was fully operational by July
• The area worst affected by fire had been cleared nibble but little rebuilding had taken place. Most commercial buildings in central areas had been repaired.
• All rail services were back to normal by August. One year later the port of Kobe was 80 per cent functional but the Hanshin Expressway remained closed.
• Replacement buildings had to meet stronger earthquake-resistance standards. High-rise buildings had to have flexible steel frames, smaller buildings had to have concrete frames with reinforcing bars to absorb shockwaves, houses were not to be built just from brick (which shakes loose) or wood (which burns too easily) but with fire-resistant materials. New buildings had to be built on solid rock, not clay, as water rises to ground-level during an earthquake, causing clay to ‘liquefy’ into mud. This results in the collapse of buildings.
• There was an increase in the number of seismic instruments to record earth movements in the region.