Do Hurricanes help shape the US East Coast?

New off shore islands are produced in shallow water and other tiny islands change shape or are down graded to reefs when very large hurricanes approach. Larger islands and mainland changes are typically a wider or narrower beach. Neil

Here's a fun applet for getting hurricane track information: http://www.rsmas.miami.edu/~geoff/hurrframe-yr.html

Certainly Cape Cod has been re-shaped by storms. Cuts through the outer beaches, chunks of mainland falling to the beaches below. I have a cool photo of a road that just ended at a sandy cliff 50' high.

Hi LittleK,

Yeh, I guess I knew about the small scale erosion of islands and capes and stuff. I was more wondering about the real large scale shape of the coast around Georgia and Florida.

Your picture of the Cape sounds great though. Any chance you can post it?

Best Regards,

Hurricanes move quite a bit of sand around so I'd guess they do help to some extent. Beach is either eroded or deposited pretty quickly in some areas.

The area shown in the pinkish hue on this map should be the area most affected.

Interesting map Fishin.

The pink layer is fairly even along all coasts. But the only area which is a darker red is right along the section of coast I was wondering about.

What does this map show exactly? Is it depth/height, or material composition?

Best Regards,

Oh sorry, I guess I should have explained the map a little. It's a topo of the Atlantic Ocean's floor. The pinkish is the shallow coastal waters. The blue is deeper water which wouldn't get as churned up by the big storms.

It's kind of hard to see exactly what's going on, but you get the idea.

LittleK,

Yeh, it looks like what some people expect will happen to California one day

Fishin,

If it's a Topo, then it would seem that a layer of "pink" has been removed right around Georgia. I don't see any other similar "erosion" elsewhere in the image.

It might be evidence for what I suspect, but it could also be a coincidence I guess. I'm not sure.

Thanks,

i know that pic of that road littleK, just past nauset lighthouse.

Once I thought I saw you
in a crowded hazy bar,
Dancing on the light
from star to star.
Far across the moonbeam
I know that's who you are,
I saw your brown eyes
turning once to fire.

You are like a hurricane
There's calm in your eye.
And I'm gettin' blown away
To somewhere safer
where the feeling stays.
I want to love you but
I'm getting blown away.


hope ya don't mind a little singin' here . . .

If you know the picture, you know it from my little website. It is indeed just past Nauset light (or one of those lighthouses that they keep having to move because the land is falling into the ocean).

we go up that road almost daily,,,,,you can hook a left and follow the dirt road around til you get to the highest point of the dunes, where the seashore fire road starts that leads to marconi. it's chained off but you can get by it if you really want to and know how,,,,
familiar ground, great picture K.

Re: Do Hurricanes help shape the US East Coast?


I found this forum while Googling for something else. I'll try to keep the facts generalized, and the geologic details to a minimum in my reply...

Ocean waves [in general] transfer energy to a depth of one-half of their wavelength (lambda). Coastlines tend to have some curvature, and the tidal basin just offshore tends to be comprised of a concave-upward surface. As a result of all of this, incoming waves experience drag on the tidal basin and shoreline and are subsequently refracted. Since we are dealing with curved features, waves rarely crash ashore in a straight line.

As waves do crash ashore, and sediment [sands, shells, etc.] are picked up and erosion occurs. Next time you are at the beach, watch how the dirty wave rolls up the beach and curves, or drifts, slightly along the beach as it falls back toward the ocean. This effect occurs all along the wave fronts that are striking at olbique angles due to the curvilinear nature of shoreline. This sequential pattern of wave front striking, rolling out, and falling back to the ocean creates a migrating sheet of sand along the beach. This erosional process is commonly referred as Longshore Drift:





On the beach-scale, wind waves do sculpt the geometry of the beach all the time. Build a seawall perpendicular to the beach and you find sand piling up on one side of it in one season. Build a dam upstream of a river that is supplying sand for the beach, and in a few years the beach starts to thin out. With a hurricane, yes the wind waves are much larger, and half-lambda will be much deeper. However, the amount of rainfall inland will generate flooding and transport of immense quantities of sediment that a hurricane would displace at the beach. Off-setting erosional processes.


At the seaboard-scale, plate tectonics is the main process at work. Referring to Fishin's image of the topography of the mid-Atlantic Basin, note the location and geometry of the Mid-Atlantic Ridge. That is where sea-floor spreading has been occurring for about 250 million years or so. Mentally piece together the southeast coast of the United States to the northwest coast of the African Continent. Use the fracture traces and the Mid-Atlantic Ridge as a guide. You will see that the whole Eastern Seaboard fits quite well with Africa and parts of southern Europe:



I'll refrain from discussing the mountain building event that created the Appalachian Mountains. However, check this easy-to-follow graphic:

www.wm.edu/geology/virginia/tectonic_history.html


Now, back to hurricanes. What hurricanes will affect are areas of recent deposition in what would normally be in calm, shallow sedimentary basins. The Mississippi Delta and the Gulf of Mexico, for example. Deltas are loosely classified into two main groups: wave-dominated and tide-dominated. Some distributaries and mouth bars will be completely destroyed, let alone re-arranged. Channels clogged with sediment recently deposited by a storm surge will be forced to jump-channel [avulsion], and create a new distributary channel. This change in coastal geometry would be noticable at a pretty large scale, such as a view from an airliner cruising at an altitude of 30,000 feet.

Wordy, I know.

Hope it helps though! If there is one take-away from all this it is:

Geology is scale-dependant.[/u]

Re: Do Hurricanes help shape the US East Coast?


So, if I understand all this, you're saying the answer to the question is, "No, Hurricanes don't affect the shape of the US Coastline".

Welcome to A2K by the way, and thanks for your detailed input.

Best Regards,