Islands Below Sea Level

On August 15, 2010 · 4 Comments

Are there any islands below sea level? The question seemed absurd on its surface when I noticed it lodged in my web logs in the form of a search engine query. However I’ve learned to not be so dismissive. I’ve uncovered increasingly obscure artifacts and encountered surprisingly unusual situations in the years I’ve the written the Twelve Mile Circle. If someone asked me the question directly I’d probably respond with a clarifying question before exploring an answer, "are we talking about oceanic islands or islands in general?"

Oceanic

The idea of an oceanic island totally below sea level defies logic. An island placed upon the sea but found below sea level is — by definition — below the sea. It’s not an island. It’s part of the seabed floor even though it may rise very, very close to the surface. It may even pop into view briefly when the winds push waves in a certain manner or when the the tides are particularly strong. We’ve probably all seen shoals or sandbars that become visible from time-to-time but I wouldn’t consider them "islands below sea level."



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Atolls provide an interesting situation. A coral reef forms around an island that later sinks below the surface, leaving behind that classic ring enclosing a lagoon, the epitome of tropical paradise. One sometimes sees references to the underpinning of an atoll’s lagoon as an island below sea level. I think of the atoll itself as the island proper and the rest of it as a lot of former island.

It is possible that part of an oceanic island can dip below sea level. Hispaniola provides an excellent example.



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Lago Enriquillo in the Dominican Republic scores high on a number of superlatives: it’s the largest lake and the lowest elevation in the Caribbean. Its shoreline is also the lowest dry land found on an oceanic island anywhere on the planet. The land here dips down to 39 meters (128 feet) below sea level. If that weren’t enough, its infested with saltwater crocodiles which has nothing to do with today’s topic but I thought it was fascinating and I’m including it anyway. Wikipedia has a great page about this location if you’d like to know more. Nonetheless, Hispaniola overall is not an island below sea level. Only a small portion of it fits within that definition and even then it’s a complete anomaly.

There seems to be an enduring urban legend or myth focused mainly in the Caribbean. I kept encountering as I poked around the Intertubes looking for examples and explanations. Some people believe, and with very firm convictions from what I could tell, that at least a handful of Caribbean islands are below sea level. It has become conventional wisdom in some corners of the basin.

I saw various attempts to explain and dispel this erroneous conclusion. A low slung boat a few miles out to sea would be bobbing along the waves’ troughs and crests. The line of sight might even be affected by the curvature of the earth. It could appear to a casual fisherman that he’s actually looking "down" at an island from his distant vantage point under the right circumstances. It would be an optical illusion but apparently one that’s convincing enough to spawn a myth.


Inland Islands

There are plenty of islands that aren’t set upon the seas, but spread along the abundant lakes, ponds and rivers of our world. Just as there are plenty of patches of dry land found below sea level, there are also bodies of water that collect within them and some happen to have islands. Lago Enriquillo, mentioned above, provides an excellent case study. It contains three islands that poke just above its surface: Isla Barbarita, Islita, and Isla Cabritos. I examined a number of geo-tagged images on photo sharing websites and these little interior islets all seemed to have maximum elevations that are safely below sea level.



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I found several other instances of islands below sea level, whether naturally occurring or affected by the interference of mankind:

  • Bethel Island is a significantly populated place in the California’s Sacramento-San Joaquin River Delta [map]. Most of its 3,500 acres are below sea level with levees protecting 3,700 residents when the river runs high.
  • Canvey Island sits on reclaimed land in England’s Thames estuary, separated by water from the rest of Essex and protected by 15 miles of seawall [map]. Nearly 40,000 people live here quite nicely in spite of frequent flooding.
  • The Caspian Sea is 28 meters below sea level with at least 26 islands including some that are significant in size, e.g., Ogurja Ada [map].
  • The Netherlands is famous for its reclaimed land, with huge swaths located below sea level behind an elaborate system of dikes. There are many, many instances of islands below sea level there.
  • I guess technically parts of New Orleans could be considered islands below sea level too, as was all too apparent in the aftermath of Hurricane Katrina. I’ve been to New Orleans dozens of times over the years and I have a hard time conceptualizing the city as an "island" even though it’s surrounded on all sides by water (albeit only narrow drainage canals in some instances).

Back to the original question: yes, there are instances of islands below sea level, just not the ones found on the open ocean. Well, assuming one doesn’t believe in Atlantis which is a completely different issue.

geography

On August 15, 2010 · 4 Comments

4 Responses to “Islands Below Sea Level”

  1. Hamish says:

    You forgot Lulu Island which is completely occupied by the city of Richmond, BC (with some 170k people). Significant parts of it are at or below sea level. It is protected by large levies and dykes. Another fun fact is that Lulu island is named for a can-can dancer during the Klondike gold rush!

  2. Lincoln Ho says:

    Could it also be that ‘sea level’ occurs at different heights depending on your position on the Earth?

  3. Chris B says:

    It is isn’t quite right to say about Canvey that ‘people live here quite nicely in spite of frequent flooding.’ The last big flood was in 1953, when 58 people died on the island. The sea wall has thankfully stopped flooding since then….. another flood now could have dire consequences.

    But it certainly is an unusual place.

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