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Chapter 2:
Landforms and earthquakes
In the previous chapter we saw how earthquakes
can produce a variety of waves, and that they can be helpful in providing information about the earth’s great tectonic plates and even about the nature of the centre of the
earth. In this chapter we look at how earthquakes alter
the landscape. To do this, we will first look at the example
of the Alaskan earthquake of 1964. Then we will look at
how repeated earthquakes can give rise to some dramatic landscapes.
The Alaskan earthquake
The great Alaskan earthquake, which lasted for about three minutes, was felt over a large area of Alaska and in parts of western Yukon Territory and British Columbia, Canada. It occurred in a region of the world with quite a small population; so although 125 people were killed (110 from the tsunami – often called a tidal wave – 15 from the earthquake), this was very low by most earthquake standards. For the same reason, damage costs were also quite low.
The epicentre was under Prince William Sound (now famous for the Valdez oil spill), but many of the most serious effects occurred elsewhere. For example, at Anchorage, about 120 kilometres northwest of the epicentre, there were large surface vibrations and landsliding.
landslides affected many properties that had been built on soft rock, including the downtown business section.
A huge area – 520,000 square kilometres – around the earthquake focus was moved vertically. About half of the area was lifted up; the rest sank lower. The major area of uplift extended northeast from southern Kodiak Island to Prince William Sound. The biggest uplift was 15 metres, while the biggest drop was 2.3 metres.
This shock generated a tsunami that devastated many