StarDestroyer.Net BBS

 Post subject: Affects of A tidal wave on the Outer Banks

Posted: 2012-04-19 08:41pm 

What precisely would one expect to happen to the Outer Banks of North Carolina, if a tidal wave were to smash into them? I get that they would be swept away, but would they significantly decrease the waves power? Would the Banks return after a few decades due to shifting sandbars and such?

 Post subject: Re: Affects of A tidal wave on the Outer Banks

Posted: 2012-04-19 10:00pm 

How tall is the wave? A tsunami an inch high can be detectable, on the other hand ones over a hundred feet tall may be plausible, and the tallest wave of any form known was around a thousand feet high but resulted from suspected melt water bursting out a glacier. Hurricanes have actually broken new inlets into the banks a number of times only to have the gaps close back up, and at least one major inlet was closed by a giant sand dune. The gap shown below was caused in 2003 by hurricane Isabel.



If a wave was big enough it'd sweep away everything, but all those islands behind the main barrier chain would provide some basis for reestablishing barrier islands through longshore drift of sand. If they'd ever completely reform would depend on the how bad the damage was, and how bad the hurricane seasons were for years afterwards. Its possible it'd come back, its also possible the entire coastline would simply change... as sea level rise may do anyway. If a Japan class tsunami would be big enough to eliminate the islands, well, I think it'd destroy the thinner but not thicker points based on the Google earth images of the damage. The 2011 Japan quake however also SANK the land by as much as a meter, a similar sinking could submerge a lot of land that might otherwise survive. In Japan the land loss from sinking was minimal because even the flatter parts of the coastline tend to have steady increases in elevation.

 Post subject: Re: Affects of A tidal wave on the Outer Banks

Posted: 2012-04-19 10:08pm 

What I had in mind was more of a tidal wave caused by a asteroid impact, something like the movie 'Armageddon'.

 Post subject: Re: Affects of A tidal wave on the Outer Banks

Posted: 2012-04-20 10:48am 

Hurricane Irene damaged the banks extensively. There is a repository of satellite images here. One breach was around 100 feet wide and 8 feet deep.

This paper details the damage caused by tsunamis on the barrier islands of Colombia. It seems to indicate that while the water literally wipes the surface of the islands clean, most of the damage to the underlying sand bars and such is due more to earthquake or pre-tsunami subsidence. While the waves from a theoretical asteroid impact would be larger and more powerful than those caused by the tsunamis, most likely, I don't know how "deep" the damage would be, so long-term affects would be primarily be effected by what the weather is like post-tidal wave. If it is normal, you would probably expect the islands to recover, although they would be altered in size and shape (and new channels would likely connect the sounds to the open ocean).

I don't know the Outer Banks that well, are any of those islands forested? Or are they just sandy, with grass of some sort? Because trees actually do a very good job of helping mitigate damage caused by tsunamis and flooding.

 Post subject: Re: Affects of A tidal wave on the Outer Banks

Posted: 2012-04-21 03:17pm 

A tsunami probably would erode less land than strong hurricane because tsunami lasts maybe half an hour while hurricane can last for a day or more. Hurricanes also bring storm surge which can reach 5 - 6 m above normal sea level which is kinda like medium sized tsunami that lasts many hours and allows wind driven waves to penetrate inland causing erosion.

 Post subject: Re: Affects of A tidal wave on the Outer Banks

Posted: 2012-05-01 11:06pm 

for a hurricane, if you give me the wind speeds, wave chareteristics, storm surge height and starting beach slope, i can give you an estimate of the new beach afterward and how long it'd take to form.
(of course, as soon as the hurricane is over all those characteristics change again and the beach starts changing to a new profile similar to the original. In a week long storm last year we lost about 2.5m of sand height. Ie the beach line tried to move back about 25m)

For a single hit tsunami - it might be possible to estimate the 1st stage erosion caused by overwash, and then the 2nd stage channelling caused by runback. Again, beach characteristics are needed.