Wednesday, September 26, 2012

Wednesday search challenge (9/26/12): Why are the coasts SO different?

The other day I was standing in a friend's office at the Googleplex.  On his wall he had a large, very high-res map of North America.  Interestingly, it was black and white, which makes your eye see the landforms in a very different way.  

As I stood there looking at it, I noticed something I'd never seen before:  the East Coast and the West Coast of the US are very different... Yes, I know they're very different culturally (LA vs. NY; TMZ vs. NPR; etc.).  But what I saw for the first time was how topographically different the coasts are from each other.  That surprised me.  

Here are a few side-by-side images from Google Earth to give you a sense of what I mean.  I've taken 3 overview shots at different resolutions so you can see what I mean.   (Remember that you can click on the images to see them at full size.) 
Here's an overview of both coasts.  What I saw was that the East Coast has LOTS more islands and barrier reefs than the West Coast.  That struck me as being really, really different.  
Here's a closer in view:  
 Do you see what I see?  There are lots and lots of very low-lying islands in the east than in the west.  (Note that I didn't try to cherrypick really good locations--these samples are from the same latitude on the West Coast and the East Coast and are pretty representative of the topography.  
Finally, here's a real closeup of two locations West vs. East.  Now the difference is really clear.  

And now for the challenge: 
Or, to be more precise: 
Why is the East Coast topography dominated by low-lying fringe islands, while the West Coast of the US is mostly without islands.  (To be sure, there are a few, but they're pretty jaggy and stoney, while the East Coast islands are mostly sandy and flat.)  
Can you figure out why?

As usual, please let us know what path you followed to find an answer, and about how long it took you to do so!  

Search on! 


  1. I can't claim this as a great authoritives source, but

    Took about 5 minutes.


    #1 - [why are the east and west coasts of the united states topographically different]
    #1 - [reason for us topographical variation]
    #3 - [why does the east coast have more islands than the west coast]

    Looks like it has to do with a number of factors, but primarily with plate tectonics. The short continental shelf caused by the westward drift of the North American continental plate (and it's collision with the Pacific one) doesn't allow the sedimentary build-up over time that typically leads to barrier island formation.

  2. Plate tectonics. More specifically as the North American continent moves very slowly westward it overrides the Pacific and Falleron plates, while there is spreading between the North American and European plates in the Atlantic (there is no Atlantic plate). As the subduction zone on the West Coast is very close it shore the continental shelf and slope are both very steep meaning that the ocean gets very deep very fast. Whereas on the East Coast the shelf and slope are much more gradual.

    North to both Washington and Maine and you will find bedrock islands shaped by ice ages. As you move south on the east coast you move from the rocky islands into the region of terminal moraines (Cape Cod and New York's Long Island) before moving into the sandy islands which I believe you are looking at. These are caused by sediment motion down rivers which then are deposited into relatively shallow ocean water. As storms come along they churn this sand up and distribute it up and down the shore. After a while these start a procession of dune forming and migration seawards and rivers start to get somewhat trapped behind the dunes. After a time and plant colonization these islands become a relatively stable shelter for the estuaries from wave action. On the west coast this sediment is deposited too deeply off shore in most locations and the slope is also too steep to support the island and dune formation process.

    - No searching, just what's left over from college

    1. nice explanation - impressive grey matter RAM
      that CC education seems to have paid off as you seem to have developed your own onboard Goo resource.
      Between your explanation and Judith's (below) I have a better understanding of the areas where land and water meet...
      Guessing if Dan poses an Antarctic/ Patagonia search you will be on top of that one too...& maybe even sandhog questions?
      anyway, thanks & fwiw: in your "5 Ws about", it's Boeing... unless that's some sort of Airbus pwned thing...✈ Dīrigō

    2. Thanks, the Kerguelen Islands question was one of the more fun ones, as I remembered the story and the location of the islands, but not how to spell them (Boeing was just from typing fast)! That time I had to start with using Google Earth to 'go there' and find the name which + india and terrane pulled it up.

      Anytime H2O and land interact forcefully it's cool, though for things like this they are probably a lot better explained with a drawing (on the side of a van or bottom of a kayak), and a lot of other ones can be explained with little demos in the dirt or on beaches. I probably should scan some doodles of explanations like that.

      Roughly if its past ~ 40º N or S and isn't some interior plains region I'll probably be all over it. Probably not sandhog questions as the underground shot is actually from the Henderson Molybdenum Mine in the mountains of Colorado, where they are going after the orebody from underneath. As they blast out chunks it with the rest of the body sufficiently weakened, it naturally falls into their buckets. Think breaking an hourglass in half and catch the sand as it comes out the bottom, rather than trying to get on top of it and dig down in.

      Right now it ain't Dirigo, it's more 'Pamola dirige me ad somnum'.

    3. hope snoozing with the pigeons (OK, it isn't Paloma) isn't like sleeping with the fishes... maybe it's a kayak thing... or maybe something was lost in my rudimentary translation attempt... wait, now I see, it has to do with moose hybrids & knife edges - that makes more sense, but still a little Picasso-esque. zzzzzzzs are good. Keep an eye out for the Wana-games-ak until Kisosen finds you.
      (Pamola - a bird and night spirit who takes prisoners to Alomkik, near Mt. Katahdin and causes cold weather)
      Picasso minotaur
      Pamola's "Index" Finger

      Thanks again for the GeoLesson (Kerguelen was before my time on sRs so it was good to go back and read that - always good to learn new stuff) - some doodles might be helpful - Dan & Goo have some experience with that - maybe next time he is in Boston you two could chat it over while paddling the Charles.
      Checked the Climax Molybdenum/ Freeport-McMoRan Copper & Gold Inc. site - an impressive effort, but doesn't that set the stage for a Rocky Mt. high sink hole?
      You might keep this in mind if the snowpack & runoff cooperate next spring & paddle what's left of this mountain/high desert pond:
      the other Big Sur

  3. The continental shelf on the west coast is a steep drop, but on the East Coast the shelf is wider and acts like a ramp. Barrier beaches form best where there is a small tidal range and a wave-dominated coast and there must be a relatively low gradient shelf. Just googleing 'barrier beaches', about 5 minutes.

  4. The West coast is at a junction of two tectonic plates. The East coast is a much older remnant. Thousands of miles from the nearest tectonic boundary. Long weathered by current and storms.

    That's just off the top of my head.

    However, you should search for, "tectonic plates", "Pacific ring of fire", "Mid Atlantic ridge", "hurricanes", "Gulf Stream current" and "barrier islands".

  5. I search united states topography and found a Wikipedia article which provided an answer. However, I need to confirm it, so I went on the USGS website which gave me information summarized by the phrase:

    "flooded river valley east coast versus the tectonic-shaped west coast"

    When I searched that I found information from a geology class at Tulane University which provide the following information:

    Passive Continental Margins - A passive continental margin occurs in the interior of plate, far away from any plate boundary. Present examples of passive continental margins are the Atlantic coast of North and South America, Europe, and Africa. No current deformation is taking place along these margins because they are not close to plate boundaries. The passive continental margins developed as a result of rifting of a former larger continent.
    A passive continental margin is characterized by a broad continental shelf overlying thinning continental lithosphere. The shelf is made of relatively shallow oceanic sediments that have been shed by the continents. [barrier islands on the Atlantic coast]

    Active Continental Margins- Continental convergent margins occur where the margin of the continent coincides with a convergent plate boundary. Examples of a current active continental margins occur along the Pacific coast of South America and in the Cascade Mountains of the western U.S.
    An active continental margin is characterized by a narrow continental shelf, again composed of sediments shed from the continents.
    Submarine canyons crosscut the continental shelves. These are associated with large rivers from the continents. Erosion carved the canyons during times when sea-level was lower than at present. The submerged canyons funnel sediments to deeper water producing submarine fans where the canyons empty onto the continental rise.
    [volcanoes and tectonic plate activity occur in this area]

    It took me about 10 minutes.

  6. too broad, complex and nuanced for a quick quiz question - that said, used:
    [U.S. coastlines east vs west geology] and came up with this - plausible entry point explanation and interesting west coast island observations by Molly Samuel - from the Bay area... re: the east coast; e.g., apparently Florida was a pleistocene "Dirk Diggler" at some point - 18000 BP? ironically Dirk was a west coaster...
    about 5 minutes.
    California's Islands
    Shipwrecked on Dry Land - Molly Samuel

  7. I searched "island formation east coast". The first Google result was a Wikipedia entry on the Barrier Islands and describes theories of how they are formed, but essentially the East Coast is sandier and smaller waves, the West Coast is rockier and bigger waves. Smaller waves accumulate sand and form the islands.

    This answer took me about 1 minute of searching and a couple minutes of reading.

  8. I looked up geology and landed on which gave me some terminology to look up- "divergent margin atlantic coast" and "continental collision convergence pacific coast"

    I found this site that showed that the tectonic plate of the west coast have been pushed upwards by another plate- thus creating a relatively clean coast line.

    another page on the same site: talked about how the East coast was created- basically two plates are moving away from each other and creating rifts in the oceanic floor. But that wasn't really answering why the islands exist on the East Coast.

    When I searched for "atlantic coast formation island" I found that had a pretty nice explanation. Basically erosion and the rising and falling of sea levels created the various islands and the beaches.

    It took me around 15 minutes.

  9. [US east coast islands versus west coast topography]
    I also use the quick scroll extension on my chrome browser.
    one of the most appropriate literature was found on
    I am still reading, and can submit a detailed answer as per requirements. took me about 4 minutes to get to this point.

  10. Hola, mi nombre es Eduardo, pues comencé googleando [costa este estados unidos topografia], encontrando todo lo relacionado con la costa este de los estados unidos, añadí a la consulta el término [origen costa] y google refleja el origen mencionando que el margen de costa tiene que ver con caracteristicasd diferentes, además de tomar la erosión, profundidad, etc.

    Para la costa oeste segui los mismos pasos y encontré que esta costa es diferente por el cañon y la falla transformante en el sitio.

    Espero que mi respuesta haya sido satisfactoria!!! Tarde 17 minutos en responder

    1. Google's translation: Hello, my name is Eduardo, it started googling [east coast usa topography], finding everything related to the East Coast of the United States, added to the query term [origin coast] and reflects the origin google mentioning that the margin coast has to do with different caracteristicasd besides taking erosion, depth, etc.

      To the west coast follow the same steps and found that this coast is different for the barrel and the transform fault on the site.

      I hope my response was successful! Responding 17 minutes later

  11. I knew the answer, but I tried to work backwards based on nothing but the information in the article...

    us east coast "more islands"

    produced no useful results, simple searches like:

    more barrier islands east coast produce nothing but vacation real estate results.

    It took me about 10 searches / 10 minutes to get to the search query:

    no barrier islands west coast

    Which yields the answer in 4 of my top 5 results... plate tectonics, and the continental drift of the North American plate. The west coast is the leading edge of the plate, while the east coast is the lagging edge. The lagging edge produces a stretched-out continental shelf of very shallow coastline, which allows sand build-up, and the accumulation of the barrier islands, which are barely there from a geological perspective, not much more than glorified sand dunes. The crust dives down into the adjacent tectonic plate on the west coast, and the limited continental shelf that results is not big enough for barrier islands to form.

  12. Approximately 5 minutes. First I cut & paste your first sentence above (the "more precise" one) into Google's search box. The fifth result was for Wikipedia's entry for "Passive Margin". A quick skim through that and, just to verify, I searched Google again for "united states passive margin". The second result was for a PDF file from Universidad de Puerto Rico's Geology Dept explaining Active (West Coast) vs Passive (East Coast) Margins.

  13. Dan - forgot to mention that I started my search with Siri... she didn't have much to say about the east coast other than it was a good place to build glass stores. She then showed me a map of said coast - apparently it is somewhere near Del Rio, Texas, mmm... anyway, she must have known I was on your site as she reminded me SEPs (search engine people) tend to have a different sense of humor and that she missed her GooPals and hoped things went well in Tokyo.
    Sometimes she loses focus or emanates from a different tangent, but I like the way she says it.
    about 5 mobile minutes/traffic started to move.

    curious about the source of friend's maps... could/would you show pics?
    were they silhouettes? B&W is a perception/conception alterer.
    flood plains & deltas
    missing islands

  14. Is it more complicated than the kind of topography that the west coast's thrust tectonics creates vs. the east coast's extensional tectonics?

    I suppose if you wanted to include the vegetation near the coast that'd add the clockwise motion of the northern hemisphere's ocean.

  15. There is a fairly sharp fall-off in the continental shelf of the west coast, whereas the east coast has a longer, more gradual drop-off.

    I used Google Earth, and it took about 30 seconds, including the time to install the plugin.

  16. google: "coastal geomorphology east vs. west". result:

    basically: west coast = subduction/compression, east coat = divergence/expansion

  17. Is it because the fault line of the Juan de Fuca plate against the North American plate is much much closer the the coastline of the west coast, whereas the North American Plate extends far out into the Atlantic Ocean.

    As a result, the sea drops off quite quickly on the west coast, making it much less likely for islands to form sedementarily, whereas on the east coast sediments shift and form islands more readily in the shallows of the near Atlantic.

  18. Google: why are there barrier islands on the east coast but not the west

    Second result:

    searched in the document for "west"

    lead me to the section: "The 4 types of estuaries are:" which explains the differences between the east and west coasts.

    It took a few minutes all told.

  19. West coasts in general have deserts. Run your eye along a latitude close to Capricorn thru. S. America, Africa and Madagascar and Australia. Each land mass has desert on the west coast and tropical wet shorelines on the east coasts. In the N hemesphere it is more difficult to see but the west coasts are California/Portugal (Morocco). The answer to the question has to do with how our weather systems work (trade wind bands with offshore flow in the west compared to counter flows and onshore flows in the east). Rainfall creates large rivers on east coasts leading to deltas and muddy estuaries. Path followed to get answer = grade 4 geography that only really ment something when you actually stand on these coastlines.

  20. Because Slartibartfast thought they looked good, and the mice approved. He did save his best work for Norway, though.

  21. This is due to plate tectonics.
    About 15 min. Started with: why does east coast have barrier islands did not get much useful.
    This: no barrier islands west coast
    Which gave a good explanation.

  22. Time: About 10 seconds

    Search string: "east coast" "united states" barrier islands

    Source: "Coastal Encounters," National Park Service,

    Answer: "This is due to plate tectonics. The United States is on the North American plate which is moving in a Northwesterly direction. The West coast is the leading edge and the East coast is the trailing edge. Barrier islands form on the trailing edge.

    "The Pacific plate (mainly under the Pacific Ocean) and the North American plate meet on the West coast at what is called a subduction zone. This is where one plate is sliding under the other. Any sediments that are carried to the ocean move across the narrow continental shelf (approximately 20 miles wide) and fall into this area. There is no accumulation and therefore no barrier islands.

    "On the trailing edge (the East coast) sediments carried to the ocean have a broad plain to accumulate on. New land is being formed at the mid-oceanic ridge as the plate moves and a wide continental shelf is created. The continental shelf off the coast of Georgia is approximately 80 miles wide. Thus, barrier islands have space and sand supply to form."

  23. Source: Honors Geologly classes in college, 1971-1972. The West coast is an active tectonic plate boundary and in a constant (in geologic time) state of change. It is very young. There is a combination of strike/slip faults as the Pacific plate rotates to the North, and other faults uplifting the coastal mountains. The East coast is much older and generally stable - is is nearing old age. The area between the coast and mountains is sedimentary deposits from erosion of the Appalachian Mountains chain --which used to be at least as high as the Rockies. The sediment is slowly compacting, subsiding and eroding, and ocean erosion is wearing away the coast. Coastal islands are a result of those processes. The nearest tectonic boundary is the Mid-Atlantic Ridge, which is spreading instead of sliding. The majority of earthquakes in the East are relaxation of pressure from the most recent Ice Age, or to accomodate pressure from new sedimentation. However, as they happen within a continental plate, they tend to be felt over a much wider area, with vibrations simiar to ringing a large bell.

  24. I added [site:edu] to my search and found the answer. I'm not sure if I comprehended it though. LOL

  25. Searched [north American continent formation coasts]
    Clicked Our Changing Continent, looked at pics, cntl-f coast. Saw Pangaea. Went back. Clicked Pangaea Wikipedia. Read/Saw north America was on the west edge of Pangaea and moving west. Blah blah blah.

    Then I remembered the more obvious reason. Search Genesis 1:1.

    Genesis 1:1. In the beginning, God created the heavens and the earth. … 1:9 And God said, "let the water under the heavens be gathered into one place, and let dry land appear." And it was so. 10 God called the dry land Earth, and the waters that were gathered together he called Seas. And God saw that it was good.

  26. My second search string was "why are the east and west coasts of north america so different geologically?" This was the top link:
    Very detailed description with great visuals. The upshot is that the west coast is on the edge of 2 shifting tectonic plates while the east coast is far from any plate edges.
    Took about a minute.

  27. Is it cheating to say "Glaciers" because I know this from 5th grade? I'm from the east coast of Canada, which is tore up plenty (but she'll fly true).

  28. Alas, glaciers don't have anything to do with it...

  29. It took several tries, switching the terms around but I finally got a very definitive result with [why east west coastline difference] The answer was located at


  30. I should have added the answer to the link using search terms [why east west coastline differences] "The shape of the coast is controlled mainly by tectonic forces and climate..."


  31. I grew up on the West Coast, father inland on an Island within Puget Sound. The only access was by boat. I have had college friends who grew up in Newfoundland and the NE that I don't know well having only travelled through a few times. My coastal knowledge is mostly of the the Pacific NW including the Sand wan Islands.
    Though I have travelled through various coastal towns, ocean beaches and forests along 101 all the way to the Mexican boarder. I'm no expert on the West Coast. As for historical knowledge I'm learning something new about the West Coast everyday.

    Puget Sound is protected by the Olympic Peninsula which includes the Olympic Mountains. Much of the Olumpic mountains were produced by plate techtonics i.e. pushing of land masses up against one another to create the Olympic Mountains. The last ICE age created much of the Puget Sound, parts of the NW, including many of the surrounding lakes to points where the effect of the ice age on the land masses eventually stops farther south.

    To obtain a good historical perspective of the West Coast you need first become aware of the coastal Native American tribes and their history. Having lived and survived along the West Coast for thousands of years provide IMO a better and more relevant perspective of how humans survived and still survive today along coastal regions.

    Much of the important parts of the West Coast coastline Extends up into Canada and then eventually into Alaska. For many years SE Alaska coastal living has effected areas farther south into Washington and Oregon. Many of the rain forests, some that still exist in SE AK were once prominent in Washington and Oregon, where much of the ancient rain forests including old growth forests have disappeared in a short amount of time.

    Forested areas from SE AK down to Northern California is considered to be a green belt. At one time around 100 years ago +/- the average age of this green belt wilderness was around 750 years. Meaning trees and undergrowth the average age of the forests was approx. ~750 years, where many trees and species were well over 1000 years old. Douglas fir at one time wasn't the prominent tree specicies. There were around eight prominent tree specicies along with ancient undergrowth. Over the years logging wiped out most of the old growth forests, replacing them with new hyrid growth of Douglas fir. Trees were genetically altered to produce a better type of tree for harvest and to go through the sawmills.

    Small areas of Old growth forests can still be found within certain National Parks, but most of the old forested areas are now gone along with many rivers and streams have dried up along with acncient undergrowth plant and animal species. Most having been around for thousands of years have disappeared within a short time span of around ~100 years.

  32. After publishing my previous post I wasn't able to find it for editing. My previous post attempted to generally address human condition including plant and animals. As for historical geological perspectives and differences between the West and East Coast, my knowledge is limited. I haven't yet studied geolocic differences which would take from several weeks to months to accomplish. There is much information however much of the data and information hasn't been compared as the two regions are different.

    It becomes difficult to separate lifeform from geologic events both historically and current real time as the two perspectives are inter connected, relying on one another. You can concentrate on differences between the two different areas (west and east coast) geologic events that have and are still occuring. However where does that leave you as there are many differences between perspectives of geologic data and how it is acquired. IMO it is better to start with a lifeforms including human populations in order to attempt to explain differences between geologic data. Unless perhaps you have an actual study outlining geologic differences between two different areas. I feel you need to start with a premise to outlining a study with goals vs just randomly pointing out geologic differences between two different areas. I support pointing out geologic differences under the guise of an outlined study, along with various goals your trying to achieve.