Tsunamis in lakes
A tsunami is a series of water waves caused by the displacement of a large volume within a body of water, often caused by earthquakes, or similar events. This may occur in lakes as well as oceans, presenting threats to both fishermen and shoreside inhabitants. Because they are generated by a near field source region, tsunamis generated in lakes and reservoirs result in a decreased amount of warning time.
Modern example[edit]
Askja[edit]
At 11:24 PM on 21 July 2014, in a period experiencing an earthquake swarm related to the upcoming eruption of Bárðarbunga, an 800m-wide section gave way on the slopes of the Icelandic volcano Askja. Beginning at 350m over water height, it caused a tsunami 20–30 meters high across the caldera, and potentially larger at localized points of impact. Thanks to the late hour, no tourists were present; however, search and rescue observed a steam cloud rising from the volcano, apparently geothermal steam released by the landslide. Whether geothermal activity played a role in the landslide is uncertain. A total of 30–50 million cubic meters was involved in the landslide, raising the caldera's water level by 1–2 meters.[8]
Spirit Lake[edit]
On March 27, 1980, Mount St. Helens erupted and Spirit Lake received the full impact of the lateral blast from the volcano. The blast and the debris avalanche associated with this eruption temporarily displaced much of the lake from its bed and forced lake waters as a wave as high as 850 ft (260 m) above lake level on the mountain slopes along the north shoreline of the lake. The debris avalanche deposited about 430,000,000 cubic metres (350,000 acre⋅ft) of pyrolized trees, other plant material, volcanic ash, and volcanic debris of various origins into Spirit Lake. The deposition of this volcanic material decreased the lake volume by approximately 56,000,000 cubic metres (45,000 acre⋅ft). Lahar and pyroclastic-flow deposits from the eruption blocked its natural pre-eruption outlet to the North Fork Toutle River valley at its outlet, raising the surface elevation of the lake by between 197 ft (60 m) and 206 ft (63 m). The surface area of the lake was increased from 1,300 acres to about 2,200 acres and its maximum depth decreased from 190 ft (58 m) to 110 ft (34 m).[9][10]
Hazard mitigation for tsunamis in lakes is immensely important in the preservation of life, infrastructure and property. In order for hazard management of tsunamis in lakes to function at full capacity there are four aspects that need to be balanced and interacted with each other, these are:
When all these aspects are taken into consideration and continually managed and maintained, the vulnerability of an area to a tsunami within the lake decreases. This is not because the hazard itself has decreased but the awareness of the people who would be affected makes them more prepared to deal with the situation when it does occur. This reduces recovery and response times for an area, decreasing the amount of disruption and in turn the effect the disaster has on the community.
Future research[edit]
Investigation into the phenomena of tsunamis in lakes for this article was restricted by certain limitations. Internationally there has been a fair amount of research into certain lakes but not all lakes that can be affected by the phenomenon have been covered. This is especially true for New Zealand with the possible occurrence of tsunamis in the major lakes recognised as a hazard, but with no further research completed.