Tsunamis in lakes: Difference between revisions

Inland tsunami hazards can be generated by many different types of earth movement. Some of these include [[earthquake]]s in or around lake systems, [[landslide]]s, debris flow, rock avalanches, and [[Ice calving|glacier calving]]. Volcanogenic processes such as gas and [[Mass flow rate|mass flow]] characteristics are discussed in more detail below. Tsunamis in lakes are very uncommon.

[[File:Tsunami comic book style.png|thumb|Figure 1: Diagram showing how earthquakes can generate a tsunami.]]

Tsunamis in lakes can be generated by [[fault (geology)|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.<ref>{{sfn|Ichinose .G.A, et al; |2000</ref>}}

These tsunamis are of high damage potential because they are contained within a relatively small body of water, and are near a field source. Warning time, after the event, is reduced, and organised [[emergency evacuation]]s after the generation of the tsunami is difficult. On low lying shores even small waves may lead to substantial flooding.<ref>{{sfn|Freundt Armin et al. |2007</ref>}} Residents should be made aware of emergency evacuation routes, in the event of an earthquake.

[[Lake Tahoe]] may be endangered by a tsunami, due to faulting processes. Located in [[California]] and [[Nevada]], it lies within an intermountain basin bounded by faults. Most of these faults are at the lake bottom or hidden in [[glaciofluvial deposits]]. Lake Tahoe has been effectedaffected by prehistoric eruptions, and in studies of the lake bottom sediments, a 10m high [[Fault scarp|scarp]] has displaced the lake bottom sediments, indicating that the water was once displaced, 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 impact that lakes have on tsunami wave characteristics, which is different from ocean tsunami wave characteristics because the ocean is deeper, and lakes are relatively shallow in comparison. With ocean tsunami, waves amplitudes only increase when the tsunami gets close to shore, however in lake tsunami, waves are generated and contained in a shallow environment.

This would have a major impact on the 34,000 permanent residences along the lake, and on tourism in the area. Tsunami run-ups would leave areas near the lake inundated due to permanent ground subsidence attributed to the earthquake, with the highest run-ups and amplitudes being attributed to the [[seiche]]s rather than the actual tsunami. Seiches cause damage because of resonance within the bays, reflecting the waves, where they combine to make larger standing waves.<ref>{{sfn|Ichinose .G.A, et al; |2000</ref>}} Lake Tahoe also experienced a massive collapse of the western edge of the basin that formed McKinney Bay around 50,000 years ago. This was thought to have generated a tsunami/[[seiche|seiche wave]] with a height approaching {{convert|330|ft|abbr=on}}.<ref>{{cite conference|last=Gardner|first=J.V.|title=The Lake Tahoe debris avalanche|conference=Geological Society of Australia|book-title=15th Annual Geological Conference |date=July 2000}}</ref>

[[subaerial|Sub-aerial]] mass flows ([[landslide]]s or rapid [[mass wasting]]) result when a large amount of sediment becomes unstable, as the result of shaking from an earthquake, or saturation of the sediment which initiates a sliding layer. The volume of sediment then flows into the lake, causing a sudden large displacement of water. Tsunamis generated by sub-aerial mass flows are defined in terms of the first initial wave being the tsunami wave, and any tsunamis in terms of sub-aerial mass flows, are characterised into three zones. A splash zone or wave generation zone, is the region where landslides and water motion are coupled and it extends as far as the landslide travels. Next, the near field area, which is based on the characteristics of the tsunami wave, such as amplitude and wavelength which are crucial for predictive purposes. Then the far field area, where the process is mainly influenced by dispersion characteristics and is not often used when investigating tsunamis in lakes. Most lake tsunamis are related only to near field processes.<ref>{{sfn|Walder J.S, et al; |2003</ref>}}

In the event of the [[Alpine fault]] in New Zealand rupturing in the [[South Island]], it is predicted that there would be shaking of approximately magnitudeModified eightMercali Intensity 5 in the lake-side towns of [[Queenstown, New Zealand|Queenstown]] ([[Lake Wakatipu]]) and [[WānakaWanaka]] ([[Lake WānakaWanaka]]). These could possibly cause sub-aerial mass flows that could generate tsunamis within the lakes. This would have a devastating impact on the 28,224 residents ([[2013 New Zealand census]]) who occupy these lake towns, not only in the potential losses of life and property, but the damage to the booming tourism industry, which would require years to rebuild.

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.<ref>{{cite web|title=Frumniðurstöður rannsókna á berghlaupi í Öskju 21. júlí 2014 |trans-title=Preliminary results of investigations on a rock slide in Öskja on 21 July 2014 |author1=Jón Kristinn Helgason |author2=Sveinn Brynjólfsson |author3=Tómas Jóhannesson |author4=Kristín S. Vogfjörð |author5=Harpa Grímsdóttir |author6=Ásta Rut Hjartardóttir |author7=Þorsteinn Sæmundsson |author8=Ármann Höskuldsson |author9=Freysteinn Sigmundsson |author10=Hannah Reynolds |language=Icelandic |date=5 August 2014|url=http://www.vedur.is/ofanflod/frodleikur/greinar/nr/2927}}</ref>

*[[DisasterList preparednessof tsunamis]]

*{{cite journal |last1=Walder |first1=J. S., et|first2=P. al|last2=Watts |first3=O.; E. |last3=Sorensen |first4=K. |last4=Janssen |display-authors=1 |date=2003; |title=Tsunamis generated by subaerial mass flows; JOURNAL|journal=Journal OFof GEOPHYSICALGeophysical RESEARCH,Research: VOL.Solid Earth |volume=108, NO. |issue=B5, |page=2236, {{doi|doi=10.1029/2001JB000707|bibcode=2003JGRB..108.2236W }}

*{{cite journal |last1=Ichinose |first1=Gene A. |last2=Anderson |first2=John G. |last3=Satake |first3=Kenji |last4=Schweickert |first4=Rich A., et|last5=Lahren al|first5=Mary M.; |display-authors=1 |date=2000; |title=The potential hazard from tsunami and seicheSeiche waves generated by large earthquakes within Lake Tahoe, California-Nevada; GEOPHYSICAL|journal=Geophysical RESEARCHResearch LETTERS,Letters VOL|volume=27 XX,|issue=8 NO|pages=1203–1206 |doi=10.1029/1999GL011119|bibcode=2000GeoRL..27.1203I X, PAGES XXXX-XXXX}}

*{{cite journal |last1=Freundt, |first1=Armin, et|first2=Wilfried al.|last2=Strauch |first3=Steffen |last3=Kutterolf |first4=Hans-Ulrich |last4=Schmincke |display-authors=1 |date=2007; |title=Volcanogenic tsunamis in lakes : Examples from Nicaragua and general implications; |journal=Pure and Applied Geophysics; {{ISSN|volume=164 |issue=2–3 |pages=527–545 |issn=0033-4553}},CODEN PAGYAV, |publisher=Springer, |location=Basel, SUISSE|doi=10.1007/s00024-006-0178-z|bibcode=2007PApGe.164..527F (1964) (Revue)}}

*{{cite tech report |last1=Heller, |first1=V., [[|author-link2=Willi H. Hager |last2=Hager, |first2=W. H.]], |last3=Minor, |first3=H.-E. (|date=2009). [|url=https://web.archive.org/web/20120803212716/http://www.vawresearch-collection.ethz.ch/publicationshandle/vaw_reports20.500.11850/2000-2009157446 |title=Landslide generated impulse waves in reservoirs – Basics and computation]. |id=VAW Mitteilung 211, |editor-last=Boes, |editor-first=R. ed. |publisher=ETH Zurich, |location=Zurich |doi=10.3929/ethz-b-000157446}}