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Tsunamis have gained worldwide notoriety following the two devastating tsunamis that have occurred in the course of the last ten years. These natural catastrophes have demonstrated that tsunamis are high-impact disasters that can cause massive destruction and death within a few minutes of their occurrence.
The impact of tsunamis is especially considerable since the world has a higher coastal population today than ever before in history. Considering the significance of tsunamis, this paper will set out to define tsunami, explain their causes and offer some real-life examples.
Tsunami: Definition and Causes
A tsunami is defined as a series of waves most commonly caused by violent movements of the sea floor (Dudley and Lee 61). The tsunami can travel up to the coastline with the water penetrating into the coastal area leaving great devastation in its wake. The first cause of tsunami is seismic activity on the ocean floor.
The second cause is submarine landslides, which can be triggered by earthquakes. These landslides cause large displacements of water thereby generating tsunamis. Coastal volcanoes are the third source of tsunamis. If a volcano originates from the ocean bed, it can displace water and generate large tsunamis. Most tsunamis occur in the Pacific Ocean since active features such as deep ocean trenches, explosive volcanic islands, and dynamic mountain ranges surround the ocean basin (Dudley and Lee 62).
Seismic activity on the ocean floor is the most prominent cause of tsunami and Bryant reveals that earthquakes have caused 82.3% of all tsunamis that have occurred in the Pacific Ocean over the past two millennia (127). The displacement of the Earth’s surface during underwater earthquakes produces great potential energy to the overlying water.
Dudley and Lee reveal that most of these earthquake tsunamis occur at the great ocean trenches where the tectonic plates that make up the earth’s surface collide and are forced under each other (62). Submarine earthquakes can generate dangerous tsunamis and that the intensity of this tsunami is generally proportional to the earthquake magnitude (2033).
In spite of their frequency, most of the tsunamis produced by seismic activity go unnoticed since their force dies down before they reach the shore or their amplitude is so small that they go unnoticed. Bryant reports, “damaging tsunamis are often associated with earthquakes with a surface wave magnitude of 7.5 or more” (125).
Dudley and Lee state that most of the tsunamigenic earthquakes occur in small thrusts and only small tsunamis are produced by these smaller quakes (62). However, large earthquakes periodically occur and these generate large and deadly tsunamis.
The two most recent tsunamis have been caused by large magnitude subduction zone earthquakes. The devastating Sumatra Tsunami of 2004 was caused by a mega-thrust earthquake at the floor of the Indian Ocean. Igarashi documents that the aftershock zone of this earthquake was longer than 1,300km and it generated a tsunami that killed nearly 230,000 people (2049). The coastal regions closest to the source suffered the most severe damage as big and powerful waves of water hit the coastline.
The powerful North Pacific Coast tsunami of 2011 was also caused by a 9.0 magnitude earthquake and the tsunami arrived within minutes after the earthquake shaking had stopped. Igarashi reports that ground shaking was felt at 3:46 pm and the tsunami generated by the earthquake occurred within 15 minutes (2049).
This tsunami hit the east coast of Japan at a speed of 800Km/hr and destroyed property along the coast. The tsunami waves continued to wash over the coastline for hours with wavelengths reaching 30 meters. The damages by the tsunami were increased exponentially by the breach on the Fukushima nuclear power plant.
Igarashi states that while governments were indifferent to tsunamis before 2004, the devastating effect of the Sumatra tsunami changed this (2049). Governments have invested in tsunami warning communication systems due to the realization that a tsunami can be hugely destructive. There are numerous efforts today aimed at establishing tsunami warning systems to protect life and property in coastal regions.
Tabuchi reports that predicting tsunami causing earthquakes is still an imperfect science and the estimated predictions are normally wrong. Seismic and sea level data offer the best means for predicting the likelihood of a tsunami occurring and alerts and warnings can be issued if necessary. Earthquake information provides the initial tsunami threat evaluation since this data provides the fastest early indicator of the tsunami’s potential.
This paper set out to briefly research on tsunamis with focus on the causes of these features and some examples that have happened in recent history. To this end, the paper has defined tsunamis and noted that seismic activity is the main cause of tsunamis.
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It has documented how enormous earthquakes originating from the ocean floor have generated the most devastating earthquakes in the world’s history. The research concluded by highlighting the efforts that governments have made to come up with effective warning systems that can help alert people of impeding tsunamis.
Bryant, Edward. Tsunami: The Underrated Hazard. NY: Springer, 2008. Print.
Campbell, Phillips. The 10 most destructive tsunamis in history. 16 Mar. 2011. Web. https://www.australiangeographic.com.au/topics/science-environment/2011/03/the-10-most-destructive-tsunamis-in-history/
Dudley, Walter and M. Lee. Tsunami! Hawaii: University of Hawaii Press, 1998. Print.
Igarashi, Yan. “Anatomy of Historical Tsunamis: Lessons Learned for Tsunami Warning.” Pure Appl. Geophys. 168.1 (2011): 2043–2063. Print.
Tabuchi, Hiroko. “Tsunami Projections Offer Bleak Fate for Many Japanese Towns.” The New York Times. 09 April. 2012. Web. https://www.nytimes.com/2012/04/10/world/asia/tsunami-projections-offer-bleak-fate-for-many-japanese-towns.html?pagewanted=all&_r=0