How do undersea earthquakes cause tsunamis




















Moderate earthquakes can sometimes launch huge tsunamis. An example is the earthquake that occurred off Unimak Island in the eastern Aleutian Island arc, just west of the tip of the Alaskan Peninsula. The earthquake's magnitude was "only" somewhere between 7. A subduction quake acting alone to generate waves of comparable size would have needed to have a magnitude of nearly nine. When in the island volcano Krakatau was blasted into pieces in the Straits of Sunda, Indonesia, a gigantic volcanic caldera formed on the seafloor, while the volcanic debris thrown into the air came down onto the surface of the sea surrounding the former island.

This double motion from below and above set off a tsunami crashing onto the shores across the entire Indian Ocean, in many places substantially exceeding the tsunami heights from the December 26, , earthquake off northern Sumatra.

Volcano- or earthquake-induced slides of portions of the Hawaiian Islands into the Pacific, or from the Canary Islands into the Atlantic are feared to put at risk most of the coasts in and across each of these two ocean basins. While such events have low probability, they could have catastrophic consequences. Humanity has not experienced a major global tsunami from a meteorite impact into an ocean. But probably one of the most extreme tsunamis in the geological history of the earth was caused by the impact of a meteorite near what is now known as the Chicxulub structure, on the Yucatan Peninsula in Mexico.

This event occurred some 65 million years ago and caused the extinction of many species, including the dinosaurs, most likely from a global drop of temperatures due to volcanic debris and dust in the atmosphere shielding the earth's surface from the sun's energy. But the meteor impact and associated ballistic debris fallout also caused a global tsunami estimated to be on the order of 1, feet high. Evidence of this great wave continues to be found at the coasts of many continents, including the U.

A very local, but still deadly tsunami occurred on Dec 12, , in the harbor of Halifax, Nova Scotia. The explosion of a World War I-ammunition-laden freighter in the harbor set off a local tsunami, causing a foot high wall of water to rush into town. When enclosed water bodies such as lakes, reservoirs or fjords are subjected to sudden displacements of their waters by rock or landslides, they can also cause deadly and often spectacular upward surges of water on the opposing shorelines.

The declared record in historic time is held by a rockslide in Lituya Bay in southeast Alaska, triggered by the Fairweather Fault strike-slip earthquake with an approximate magnitude of eight. A huge rockslide had gained high speed as it descended into the narrow fjordlike Lituya Bay, which made the displaced water run up on the opposing rock wall of the fjord to heights of 1, feet m. The surging water stripped millions of forest trees and all soil from the entire rock wall up to this height.

Large tsunamis have occurred in the United States and will undoubtedly occur again. Significant earthquakes around the Pacific rim have generated tsunamis that struck Hawaii, Alaska, and the U. One of the largest and most devastating tsunamis that Hawaii has experienced was in from an earthquake along the Aleutian subduction Filter Total Items: 9.

Year Published: Reducing risk where tectonic plates collide—U. Geological Survey subduction zone science plan The U. Gomberg, Joan S. View Citation. Gomberg, J. Geological Survey subduction zone science plan: U. Geological Survey Circular , 45 p. Geological Survey Fact Sheet —, 4 p. Jones, Jamie L. Attribution: Western Geographic Science Center. Jones, J. Geological Survey Scientific Investigation Report —, 32 p. Year Published: Community exposure to tsunami hazards in California Evidence of past events and modeling of potential events suggest that tsunamis are significant threats to low-lying communities on the California coast.

Wood, Nathan J. Year Published: Tsunami hazards to U. Ryan, Holly F. Tsunami hazards to U. Year Published: Variations in Community Exposure and Sensitivity to Tsunami Hazards on the Open-Ocean and Strait of Juan de Fuca Coasts of Washington Evidence of past events and modeling of potential future events suggest that tsunamis are significant threats to communities on the open-ocean and Strait of Juan de Fuca coasts of Washington.

Year Published: Tsunami hazards— A national threat In December , when a tsunami killed more than , people in 11 countries around the Indian Ocean, the United States was reminded of its own tsunami risks. Year Published: Tsunamis — Scourge of the Pacific Although tsunamis occur most often in the Pacific Ocean, they can be generated by major earthquakes in other areas. Lockridge, Patricia. Filter Total Items: 6. Date published: March 5, Date published: February 1, Date published: September 18, Attribution: Science Application for Risk Reduction.

Date published: August 20, Date published: September 5, Date published: March 17, Filter Total Items: List Grid. April 10, Tsunami-evacuation sign in the city of Nehalem, Oregon.

January 26, Attribution: Natural Hazards. November 28, Southeast Asia in May Tsunami brought in dangerous waves and destruction. DOI: Geoscience Australia is committed to support Australia's capability to manage the impact of natural hazards, including tsunami. Geoscience Australia:. Geoscience Australia receives real-time data from over 60 seismic stations in Australia and more than international seismic stations.

The seismic information is automatically analysed by Geoscience Australia's seismic monitoring and analysis systems that form part of the 24 hours a day, seven days a week operations centre.

When an earthquake occurs, this system automatically computes preliminary information on the earthquake's origin time time at which the earthquake happened , location, depth and magnitude. The Duty Seismologist assesses this information and then calculates a moment magnitude, Mwp, similar to a Richter magnitude to assist in determining the potential for the earthquake to cause a tsunami.

If Duty Seismologist considers that the earthquake has the potential to generate a tsunami that may impact Australia, the seismologist sends the information to the JATWC office in the Bureau of Meteorology in Melbourne via a dedicated data link.

This process is completed within 10 minutes of the earthquake's origin time. These instruments provide real-time sea level observations that can verify whether an earthquake has generated a tsunami and, if so, monitor its path.

The data are provided by coastal sea level stations and deep ocean tsunami detection sensors. Equipped with these sea level data and the Bureau of Meteorology's tsunami modeling, specially trained JATWC staff then issue a warning that is in keeping with the determined threat level.

These warnings identify affected coastal regions, initial tsunami arrival times and whether the tsunami threat is to land or marine areas. Upon receiving the earthquake alert from Geoscience Australia, the Bureau of Meteorology issues a tsunami bulletin within 10 minutes of receiving the alert. The JATWC is thus able to issue tsunami bulletins within 20 minutes of the origin time of the earthquake.

The Bureau of Meteorology issues advice and warnings on identified tsunami threat to emergency management agencies and the public using procedures similar to those used for warnings of other severe weather or hazardous events. Procedures include:.

What is a tsunami? How do tsunami differ from regular waves? What causes tsunami? Earthquakes Most tsunami are caused by large earthquakes on the sea floor when slabs of rock move past each other suddenly, causing the overlying water to move. The largest run-up resulted from the Java tsunami that was recorded at 7. The tsunami that reach the Australia coast at Steep Point on 17 July was generated by a magnitude 7. The tsunami caused widespread erosion of roads and sand dunes, extensive vegetation damage and destroyed several campsites up to metres inland.

The tsunami also transported a 4WD vehicle ten metres.



0コメント

  • 1000 / 1000