Tsunamis are giant waves caused by earthquakes or volcanic eruptions under the sea. But as the waves travel inland, they build up to higher and higher heights as the depth of the ocean decreases. The speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Tsunami waves may travel as fast as jet planes over deep waters, only slowing down when reaching shallow waters.

Much like any other water waves, tsunamis are reflected and refracted by the topography of the seafloor near shore and by the configuration of a coastline. Occasionally, the first arrival of a tsunami at a coast may be the trough of the wave, in which case the water recedes and exposes the shallow seafloor. It took place in the bay of Lisbon, Portugal, on November 1, 1755, after a large earthquake, many curious people were attracted to the bay floor, and a large number of them were drowned by the wave crest that followed the trough only minutes later.


Notable tsunamis

Other tsunamis of note include those that followed the spectacular explosive eruption of the Krakatoa volcano on August 26 and 27, 1883, and the Chile earthquake of 1960. A series of blasts from Krakatoa submerged the island of Rakata between Sumatra and Java, creating waves as high as 35 meters in many East Indies localities, and killing more than 36,000 people. The largest earthquake ever recorded took place in 1960 off the coast of Chile, and it caused a tsunami that killed approximately 2,000 people in Chile, 61 people 15 hours later in Hawaii, and 122 people 22 hours later in Japan.

Tsunami warning system


A warning may begin with an alert by a geological society that an earthquake large enough to disturb the ocean’s surface has occurred. Meteorological agencies may then report unusual changes in sea level, and then the warning center may combine this information with data on the depth and features of the ocean floor to estimate the path, magnitude, and arrival time of the tsunami.


Depending on the distance from the seismic disturbance, government authorities may have several hours’ notice to order the evacuation of coastal areas. The Pacific Tsunami Warning Center, located near Honolulu, Hawaii, was established in 1949. It serves as one of two regional warning centers for the United States the other is located in Palmer, Alaska and since 1965 it has also served as the warning center for 26 countries organized by UNESCO’s Intergovernmental Oceanographic Commission into the International Coordination Group for the Tsunami Warning System in the Pacific.

Latest tsunami update

On 30 October 2020, a significant tsunami triggered by an earthquake of magnitude 7.0 Mw hit the island of Samos (Greece) and the Aegean coast of the Izmir region (Turkey). The event shed light once again on the complexity of warning of locally generated tsunamis of rapid onset which challenged the ability of local authorities and communities at risk to take early action. According to Turkey’s Disaster and Emergency Management Authority (AFAD), one of the confirmed victims in Turkey drowned because of the tsunami.



This event is a bitter reminder after the wake-up call on 20 July 2017, following the Bodrum Kos tsunami, to increase tsunami preparedness through enhanced sea-level detection networks, education, as well as international cooperation.

Extraterritoral tsunamis

Tsunami waves are not limited to Earth’s surface. An analysis of the Martian surface conducted in 2016, which examined the desert planet’s northern plains by using photographs and thermal imagery, revealed evidence of two separate tsunami events that occurred long ago. These events are thought to have been caused by comet or asteroid impacts.


 Dibyakalpa Tali

Content Writer (Erakina by RTMN)



One Comment

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