THE MAIN TYPES OF TSUNAMIS - GEOGRAPHY - 2025

The types of tsunamis can be classified according to two important values: the intensity of the phenomenon and the distance it travels.

A tsunami drifts out of the source that created it as a series of waves. Its speed will depend on the depth of the water, and it undergoes accelerations or decelerations depending on the seabed.

Tsunami waves in the deep ocean can reach speeds of between 500 and 1,000 kilometers per hour.

When it reaches a coast, because it is shallower, it travels at about 15 kilometers per hour. Depending on the depth of the beach, a wave that in the deep ocean is one meter high, on the shore it can grow to tens of meters.

Tsunamis can be classified according to the distance they travel from the source to the coast, and according to their intensity, using the modified Sieberg scale.

Classification based on distance

local

They come from a nearby source and have destructive effects on coasts less than 100 kilometers from the epicenter. The wave takes less than an hour to arrive.

They are almost always caused by earthquakes, although they can also be caused by a movement of the earth or a volcanic eruption.

These types of tsunamis are responsible for 90% of deaths, since there is no time to prepare.

Regional

They can cause destruction on shores up to 1,000 kilometers from the source. They take between one and three hours to arrive.

In areas outside the aforementioned region, it has practically no effect.

Most of the most destructive tsunamis are regional or local. Between 1975 and 2012, 39 local and regional tsunamis were recorded; 26 of them occurred in the Pacific Ocean and caused 260,000 deaths.

Far away

They are generated more than 1,000 kilometers away. They take 12 hours or more to arrive.

For example, an earthquake generated in Chile in May 1960 took 22 hours to reach the coast of Japan.

Classification based on intensity

Grade I

Very soft. The wave is so weak that it is only perceived in the records of the tide stations.

Grade II

Soft. The wave is perceived only by those people who live along the coast and are familiar with the sea. It is best perceived on very flat shores.

Grade III

Pretty strong. It is generally easily perceived. It causes flooding on gently sloping shores, and small sports boats are washed ashore. Produces slight damage to coastal structures.

Grade IV

Strong. It causes flooding on the coast, to a certain depth, and erodes man-made landfills. Jetties, levees and coastal structures are damaged.

Large sports boats and small vessels drift inland or out to sea. The coasts are littered with waste.

Grade V

Very strong. The coast is flooded to a certain depth. Damage to pier walls and solid structures near the sea. Coastal structures are destroyed, and erosion reaches nearby arable areas.

All vessels, even the largest, are swept inland or out to sea. Where there are river estuaries there is a great rise in these, and causes great damage to port facilities.

The wave is accompanied by a loud roar. Unfortunately it leaves many victims.

Grade VI

Disastrous. Partial or total destruction of structures erected by man at a certain distance from the coast.

It produces severe coastal flooding and trees are uprooted. Large ships are severely damaged. These tsunamis are the strongest and the ones that cause the most victims.

References

1. "Classification and propagation" in What are Tsunamis ?. Recovered in September 2017 from the Inocar Navy Oceanographic Institute at: inocar.mil.ec
2. "Tsunami Glossary" in International Tsunami Formation Center. Recovered in September 2016 from the International Tsunami Formation Center at: webserver2.ineter.gob.ni
3. "Tsunami Classification" in Scribd. Recovered in September 2017 from Scribd at: es.scribd.com
4. «Scales of earthquakes, tsunamis and hurricanes» in Radio Club Los Libertadores (July 2013). Recovered in September 2017 from Radio Club Los Libertadores in: ce2rdl.cl
5. «Tsunamis on the coast of Chile» in Sismo 24. Recovered in September 2017 from Sismo 24 in: sismo24.cl
6. «The different types of Tsunamis that earthquakes can cause» in La Tercera (March 2014). Recovered in September 2017 from La Tercera at: latercera.com