Tsunamis in lakes

A tsunami is defined as a series of water waves caused by the displacement of a large volume of a body of water, such as an ocean. This is misleading as destructive water waves are not restricted to the ocean, in the case of this article the body of water being investigated will be a lake rather than an ocean. Tsunamis in lakes are becoming increasingly important to investigate as a hazard, due to the increasing popularity for recreational uses, and increasing populations that inhabit the shores of lakes. Tsunamis generated in lakes and reservoirs are of high concern because it is associated with a near field source region which means a decrease in warning times to minutes or hours.

Inland tsunami hazards can be generated by many different types of earth movement. Some of these include earthquakes in or around lake systems, landslides, debris flow, rock avalanches, and glacier calving. Volcanogenic processes such as gas and mass flow characteristics are discussed in more detail below.

Tsunamis in lakes can be generated by fault displacement beneath or around lake systems. Faulting shifts the ground in a vertical motion through reverse, normal or oblique strike slip faulting processes, this displaces the water above causing a tsunami (Figure 1). The reason strike-slip faulting does not cause tsunamis is because there is no vertical displacement within the fault movement, only lateral movement resulting in no displacement of the water. In an enclosed basin such as a lake, tsunamis are referred to as the initial wave produced by coseismic displacement from an earthquake, and the seiche as the harmonic resonance within the lake.

In order for a tsunami to be generated certain criteria is required:

These tsunamis are of high damage potential due to being within a lake, making them of a near field source. This means a vast decrease in warning times, resulting in organised emergency evacuations after the generation of the tsunami being virtually impossible, and due to low lying shores even small waves lead to substantial flooding. Planning and education of residents needs to be done beforehand, so that when an earthquake is felt they know to head to higher ground and what routes to take to get there.

Lake Tahoe is an example of a lake that is in danger of having a tsunami due to faulting processes. Lake Tahoe in California and Nevada USA lies within an intermountain basin bounded by faults, with most of these faults at the lake bottom or hidden in glaciofluvial deposits. Lake Tahoe has had many prehistoric eruptions and in studies of the lake bottom sediments, a 10m high scarp has displaced the lake bottom sediments, indicating that the water was displaced by the same magnitude, as well as generating a tsunami. A tsunami and seiche in Lake Tahoe can be treated as shallow-water long waves as the maximum water depth is much smaller than the wavelength. This demonstrates the interesting impact that lakes have on the tsunami wave characteristics, as it is very different from ocean tsunami wave characteristics due to the ocean being deeper, and lakes being relatively shallow in comparison. With ocean tsunami waves amplitudes only increase when the tsunami gets close to shore, in lake tsunami waves are generated and stay in a shallow environment.

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Wikipedia