So many great answers from readers! I'm impressed. This is a legitimately hard question (about which you could write many PhD theses), but people figured it out pretty quickly.
The short answer to:
..is..
Note that the Pacific plater butts up against California, while the North American plate extends way out into the Atlantic. That's a huge difference, and vastly changes the nature of the coastlines as well.
As several readers pointed out, this really is a big topic, and by giving a quick answer like this, we're obscuring many fascinating details. But this isn't a geology blog--it's a blog about search and how to find it effectively. Which is why reading the details of how people searched is so interesting.
A couple of observations.
1. You need to follow the search deeply enough to get a "real" answer. Several people (including people I chatted with) found that the East accumulated sediment, but couldn't say why. The intriguing thing about what they said was that they could make up (that is, rationalize) a story very quickly. But they didn't have any data to backup what they were saying. Word to the wise: When you don't have data, you usually know it. That's when you slip over the slippery slope edge into BS. It's easy to do and we all practice it all the time. But as researchers, we need to be aware of when this happens, and be able to stop ourselves and realize that this is the time for more research.
2. Starting this search was hard. Many people had difficulty getting started with searches that worked. Once they starting including barrier islands and terms like formation or East coast or West coast with barrier island formation they started getting results. When I was doing my searching, I added the context term geology in my searches to limit the number of off-topic results and focus more on scholarly articles.
3. Follow the people chain. I did find several articles that helped me in my search. By starting with [ west coast vs east coast barrier islands ] I found an article comparing the two by Molly Samuels (an environmental reporter). Reading the comments on that article lead me to start thinking about plate tectonics because of a comment left by Brian Romans, a geologist who writes about island formation in his blog, ClasticDetritus.
All this story is by way of pointing out that following the comments in a blog is often a great way to find experts. But be sure to check their bona fides. There are lots of random people commenting authoritatively on blog streams as well. If you can't prove that they actually know something about a topic (usually because of a history of good writing on that topic), then quickly file under "don't know" and move onto people whose comments you can trust.
4. Sometimes search requires... well, searching. Many people reported having to hunt around a bit for a way to phrase their search query to get something useful. This was true for me as well. Sometimes you get lucky and your first query gets you into a space that resolves the question. For something like this, it might take a few probes to find a valuable set of results. Get in, check out the results, if you don't see what you like, move on. But learn as you go--notice the terms used, the publications and the people involved. Usually that is enough to point you in the direction you need to go.
And... for people who asked me about the black/white map that started this whole question--it was the wonderful map made by the people at Raven Maps. I have no affiliation with them other then being a fan. Here's the link to the map that started the question. You have to see the map in person to get the full effect... but the right hand side of this map is VERY different than the left hand side. Hence my question.
The short answer to:
Why?
..is..
Because plate tectonics (specifically, the nearby edge of the Pacific plate) force the western coast to be steep without much chance to accumulate the sediments needed to make barrier and fringing islands. By contrast the East Coast has a long, gently sloping grad from coastline to the next plate edge, giving sediment an easy place to accumulate.See the following map (linked from the Wikipedia article on plate tectonics):
 |
| Tectonic plates map from Wikimedia |
Note that the Pacific plater butts up against California, while the North American plate extends way out into the Atlantic. That's a huge difference, and vastly changes the nature of the coastlines as well.
As several readers pointed out, this really is a big topic, and by giving a quick answer like this, we're obscuring many fascinating details. But this isn't a geology blog--it's a blog about search and how to find it effectively. Which is why reading the details of how people searched is so interesting.
A couple of observations.
1. You need to follow the search deeply enough to get a "real" answer. Several people (including people I chatted with) found that the East accumulated sediment, but couldn't say why. The intriguing thing about what they said was that they could make up (that is, rationalize) a story very quickly. But they didn't have any data to backup what they were saying. Word to the wise: When you don't have data, you usually know it. That's when you slip over the slippery slope edge into BS. It's easy to do and we all practice it all the time. But as researchers, we need to be aware of when this happens, and be able to stop ourselves and realize that this is the time for more research.
2. Starting this search was hard. Many people had difficulty getting started with searches that worked. Once they starting including barrier islands and terms like formation or East coast or West coast with barrier island formation they started getting results. When I was doing my searching, I added the context term geology in my searches to limit the number of off-topic results and focus more on scholarly articles.
3. Follow the people chain. I did find several articles that helped me in my search. By starting with [ west coast vs east coast barrier islands ] I found an article comparing the two by Molly Samuels (an environmental reporter). Reading the comments on that article lead me to start thinking about plate tectonics because of a comment left by Brian Romans, a geologist who writes about island formation in his blog, ClasticDetritus.
All this story is by way of pointing out that following the comments in a blog is often a great way to find experts. But be sure to check their bona fides. There are lots of random people commenting authoritatively on blog streams as well. If you can't prove that they actually know something about a topic (usually because of a history of good writing on that topic), then quickly file under "don't know" and move onto people whose comments you can trust.
4. Sometimes search requires... well, searching. Many people reported having to hunt around a bit for a way to phrase their search query to get something useful. This was true for me as well. Sometimes you get lucky and your first query gets you into a space that resolves the question. For something like this, it might take a few probes to find a valuable set of results. Get in, check out the results, if you don't see what you like, move on. But learn as you go--notice the terms used, the publications and the people involved. Usually that is enough to point you in the direction you need to go.
And... for people who asked me about the black/white map that started this whole question--it was the wonderful map made by the people at Raven Maps. I have no affiliation with them other then being a fan. Here's the link to the map that started the question. You have to see the map in person to get the full effect... but the right hand side of this map is VERY different than the left hand side. Hence my question.
 |
| Raven Maps Landform of the US map |
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