Why are there so many barrier islands on the (US) Atlantic coast, but virtually none on the Pacific coast?

Question

By barrier islands I mean the narrow strips of land that lay across an intracoastal waterway like those off the Carolinas or southeast Florida. The Pacific coasts have been around much longer so one would naturally assume that it would harbor more barrier islands, but it harbors almost none.

Answer 1

The main reason is because the Pacific Coast is a very active plate margin with a steep drop off and a very narrow continental shelf. Barrier Islands don't really have an opportunity to form as well because a lot of the sediment gets trapped in the multitude of dams that have been built to try to make the western coast into an oasis, when in reality much of it is a desert.

The Atlantic Coast has been tectonically calm for millions of years, and has a very wide continental shelf. Also, I would guess that there have historically been less dams restricting the flow of sediment to the coast. However, recent construction activities and developments have shut off the sediment supply to a great deal, and we are losing a lot of the East Coast barrier islands, which had served as hurricane barriers.

Answer 2

Maybe the sea is more shallow close to the U.S. Atlantic shore than the sea on the Pacific side of the North American continent? A long continental shelf which forms a shallow sea allows sediment to built up to the point where it reaches the ocean surface (forming low islands). The Pacific side of the North American continent drops off suddenly, so the water is deeper. The same sediments build up, but since the water is deeper, the sediments never pile up high enough to reach the surface.

Why does the Pacific side have a much steeper drop-off (resulting in a deeper off-shore sea)? The North American continent is moving westward. This causes one tectonic plate to dive below the other one, forming a deep trench at the boundary between the plates just off-shore on the Pacific side. This also prevents sediment from building up on the Pacific seafloor near the American continent, because the Pacific ocean floor is diving down into the mantle, taking the sediments with it.

How is that for a theory?

Answer 3

The primary reason is that the US Pacific Coast is mostly rocky. Where it's largely sandy peninsulas and barrier islands form. However, a second factor comes into play on the west coast: It is a windward coast whereas the Atlantic coast is largely a leeward coast. That is, the prevailing wind is onshore on the west coast almost always and it blows like hell most of the time. The makes the waters much rougher and enables the waves to move the sand around more that it is moved on the east coast. Such movement is not conducive to the retention of barrier islands.

Answer 4

Wether or not a barrier island is formed depends upon two things..and what the balance between them is.
Amount of sediment:
In order to make a barrier island, you need to have sand/clay etc..some sort of sediment available in large enough quantities to actually pile up and make the island. The atlantic coast has a number of rivers columbia, deleware etc..that do supply sediment to Amount of wave energy:
If a river is dumping sediment out into a generally quiet basin, like the gulf of mexico, then the sediment tends to form a delta (i.e. the mississippi). If the shoreline is rougher (I mean higher wave energy) then the delta is never really able to prograde, or build itself out into the basin because the waves constantly rework it and push it back on to the shoreline.
Ideal conditions for barrier islands exist when the wave energy is somewhere in between the extremes so the sediment makes it into the basin, but is still reworked by longshore currents etc.. into long shore-parallel islands, barrier islands.

So...the west coast of the US is pretty much known for it's high energy shorelines (which is why surfers like it) and this high energy is simply too much for the amount of sediment being supplied to be reworked into an island. This is not the case on the east coast where the wave energy is lower, and longshore currents abound.

Answer 5

Most of the barrier islands of the Atlantic Coast are actually part of the North or South American continent the area between these islands and the continental coast has just been claimed over the centuries by the harsh Atlantic Ocean. The Pacific Ocean is much more calm (thus its name) therefore has done much less damage to our western coast. Atleast thats my best guess lol.

Answer 6

this is due to three reasons
pattern
process
landform