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.
Tsunamis are often referred to as local or distant. The type of tsunami depends on the location of the source of the tsunami and where it may strike land. The source of a local tsunami is close to the coast and may arrive in less than one hour. The danger is greatest for local tsunamis because the warning time is limited. A distant tsunami is the generated far away from a coast, so there is more time to issue and respond to the warnings.
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.
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.
Facts about tsunami:
- A tsunami is a series of ocean waves caused by an underwater earthquake, landslide, or volcanic eruption. More rarely, a tsunami can be generated by a giant meteor impact with the ocean. These waves can reach heights of over 100 ft.
- About 80% of tsunamis happen within the Pacific Ocean’s “Ring of Fire.”
- The first wave of a tsunami is usually not the strongest, successive waves get bigger and stronger.
- Tsunamis can travel at speeds of about 500 miles or 805 kilometers an hour, almost as fast as a jet plane.
- The states in the U.S. at greatest risk for tsunamis are Hawaii, Alaska, Washington, Oregon, and California.
- If caught by a tsunami wave, it is better not to swim, but rather to grab a floating object and allow the current to carry you.
- Tsunamis retain their energy, meaning they can travel across entire oceans with limited energy loss.
- Tsunami means “harbor wave” in Japanese (tsu = harbor + nami = wave), reflecting Japan’s tsunami-prone history.
- Scientists can accurately estimate the time when a tsunami will arrive almost anywhere around the world based on calculations using the depth of the water, distances from one place to another, and the time that the earthquake or other event occurred.
- Hawaii is always at great risk for a tsunami – they get about 1 per year and a severe one every 7 years. The biggest tsunami that occurred Hawaii happened in 1946, the coast of Hilo Island was hit with 30 ft waves at 500 mph.
- In 2004, the Indian Ocean tsunami was caused by an earthquake with the energy of 23,000 atomic bombs. After the earthquake, killer waves radiating from the epicenter slammed into the coastline of 11 countries. The final death toll was 283,000.
You can read about also kookaburras: KOOKABURRAS THE LAUGHING JACKASS/ Erakina
-by Dibyakalpa Tali (21/11/21)