what is the indentation left in the land after a tsunami wave crests and crashes down on land?

Question

im specificly looking for the dent that would be left behind in the landmass after a huge wave hit land the name of the formation that would be left in the geological record from a tsunami making land fall in the past.

to be more specific my question comes after remembering about a discovery channel program where the narrator referred to this huge dent or slice/cut into the rock there next to where he was standing and said that it was initially a under water volcanic eruption that had originated from the hawaiian islands and that it was of such great magnitude of being at least 100 ft tall ect ect he referred to the dent as with calling it by a certain name can anyone help?

Answer 1

I think you may be asking about a bench collapse. A bench collapse is a landslide along the shore where lava has built up over a sandy beach. As the lava accumulates, the soft sediment underneath it eventually gives way and it starts off as an undersea landslide. As it accelerates the shoreline collapses along with it, and the resulting motion pulls water down with it creating a tsunami wave.
See this explanation:
http://hvo.wr.usgs.gov/volcanowatch/1994/94_08_26.html

While the shoreline topography will change how a tsunami affects the shore, many tsunamis that approach and overtake a shoreline will leave behind sediment rather than eroding it. The tremendous energy of the wave will strip the sand off of beaches and carry the sand and mud inland, and as the water drains back out it has less energy so much of the sediment load drops out leaving a deposit behind. These are sometimes identified and used to evaluate prehistoric tsunami events. Identification of deposts left behind by a tsunami is difficult where there is no historical record because large storms like typhoons or hurricanes can deposit large layers of sediment also. Here is an example:
http://www.oregongeology.com/sub/earthquakes/Coastal/CoastalHazardsMain.htm
And some research being done:
http://soundwaves.usgs.gov/2005/02/

Erosional features do form as a result of tsunamis. Some of these are channels and cuts through beach ridges, scours, scour ponds, and one that was newly reported after the Sumatra tsunami called beach pedestals. Beach pedestals are mesas formed as the result of erosion by wave runup. Since backwash tends to come back through the topographic lows, it will leave these high areas behind, which may have steep walls and flat tops.

Another feature left behind by tsunamis are deposits of boulders. I have seen one on Barbados that is the size of a large truck, that because it is made of coral rock, can be identified as being clearly upside down. The corals in the rock are all pointing downward, opposite the direction in which they grew. That rock has been dated as being deposited about 4600 years before present.

Answer 2

I don't remember anything like that from either geology or oceanography classes. I wasn't aware that tsunamis made dents. It's a lot of water, but anything that it swept away would get pulled back in the "dent" when the water sweeps back. I don't think you'll find evidence like that in any geological record. I mean, think about it--tsunamis happen near the ocean, right? What kind of geological record would you find on a beach? It's just sand or rocks or stuff that doesn't keep a good record. Unless you have some building with a high-water line, I don't think there'll be a long-term record of a tsunami wave.

Answer 3

I don't believe a tsunami can make a dent. It is a mass of water that propels across the land. You might be referring to a tidal wave that is a high wall of water that crashes into the land. However, I am unaware of any names that are caused by the destruction.

Answer 4

The only thing I can think of is that it would create an erosional surface, which might be an unconformtiy in the rock record? Perhaps they used the term 'inundation'? Tsunamis consist of multiple waves that run-up onto the landmass, eroding away sand in one place and depositing it in another. Here are a couple of websites that might help.

http://geology.com/articles/tsunami-geology.shtml
http://walrus.wr.usgs.gov/tsunami/basics.html

Answer 5

generally a wave will not make a 'dent'.
it may cover the land mass with water and push things around, but I doubt that anything soft enough to be dented by water will remain after the wave has passed.