Islands of Portland

Welcome to Greenhouse Earth–Portland edition. The Portland archipelago awaits your descendants. Update: Someone pointed out these maps showing the Missoula floods–Very cool!

See the other Drowned Cities maps…

See the original–Burrito Justice & Brian Stokle’s map of San Francisco. This is the second in a series of sea-level-rise maps. Seattle was the first. There are more cities in various stages of completion, and I’ll be posting them as they are finished. Right now, I’m working on all the major North American West Coast cities, except for San Francisco, which has already been done. The loose confederation of future city-states is slowly taking form. What fascinates me the most about this project is the landforms, bays, seas and other geographies that emerge. In Seattle’s case, the landforms were compelling up close–the hills and valleys of Seattle’s glacial topography made amazing islands and passages. For Portland, it gets interesting as you zoom out–the inland seas, islands, and fjords are what make this map fascinating to me. The Cordilleran Ice Sheet had massive influences on the geologies of both cities, but only indirectly here. The sheet didn’t extend this far south, but the Missoula Floods swept through many times–the result of breaking ice dams from the glaciers upstream.

Sea level rise of this extreme has been estimated to take anywhere from 1,000 to 10,000 years, which may seem like a long time in the context of a single human life span, but in terms of human civilizations, it’s really not. Anyway, this end point is not really important. The real damage will come long before then–a small fraction of this 215′ level will devastate coastal cities.

25 thoughts on “Islands of Portland

  1. I’d like to buy this map but only the Montreal Archipelago seems to be for sale; any word on if/when this will be available?

  2. Pingback: What the West Coast would look like under 260 feet of sea level rise - The Washington Post

  3. Fascinating “after” map for Portland. But is there a “before” overlay (at least with main roads marked) so I can see how deeply my house would be submerged?

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  5. Wonderful imagery! Our ever-changing planet will keep on keepin’ on, long, long, long after we’re gone.

    When the Missoula Floods swept through some 15,000 years ago, what is now Portland is estimated to have been 400 feet underwater. Crown Point in the western Gorge was probably the highwater point. The massive movement of silt flooding down through what we call the Willamette Valley today created the rich soil and fertile farmlands the region is known for.

    Key difference: the transformation presented here will be brought about by salt- or brackish water. Even after this inundation recedes in another 10,000-20,000 years, it will likely take thousands more years before plant life (much less grapes or kale) can appear.

  6. What really surprises me is the lack of vision that comes with this idea of the world with higher sea levels. People will adjust, animals will adjust or die out. No one is talking about the effect of so much water will have on the tectonic plates. My guess it will cause quite a few more earthquakes than we see as a norm. What kind of effect will it have on the weather. Will we start seeing hurricanes on the west coast, maybe typhoons. Will it change the currents in the oceans. How will it change the seasons? Will continents just slip under never to bee seen again?
    These are all things that need to be asked…

  7. I don’t understand this map. Portland is 80 miles from the coast. It will not be flooded as sea levels rise.

    • Distance from the coast is irrelevant. What matters is elevation above sea level for the city and everything between it and the sea. Portland is essentially at sea level, and is connected directly to the ocean by the Columbia River.

  8. Whatever happened to science that was based on actual observations rather than over-the-top speculation? Even the IPCC says that sea level rise “might” reach 7 inches per century if certain trends continue. Your map shows 215 feet, or 368 centuries worth (36,800 years). Sorry, but I’ll bet the other way — that apsidal precession of the earth’s axis will bring still another ice age before we get a sea level rise anything close to 12 feet.


      These maps are just the extreme endpoints. The damage from sea level rise to ecosystems and human societies will be immense long before the world gets anywhere near these scenarios. I don’t think that anyone is speculating any sort of precise timeline for all the ice sheets to melt. One estimate I found says anything from 1,000 to 10,000 years ( In the scale of human lifetimes, it may take scores of generations. In terms of geological time, it’s happened before and it will certainly happen again. The danger comes with the speed in which it happens, and we humans are certainly speeding up the process.

      • At the beginning of the Pleistocene Ice Age (which we are still in), there were no known ice sheets. Were the land elevations different than they are now? Of course, but so were the locations and elevations of the land masses. What I still have not been able to find definitive research on is the long term effect of the weight of ice sheets on various land masses. It is well known that certain land masses are still rising after the weight of the late Wisconsin glaciation was lifted. I understand, for example, that Manhattan Island is still rising even now. I have yet to find anything that tries to examine the so-called “normal” elevation of sea level or “normal” global temperature. It is mostly fanciful “what-if” scenarios — what if the sea level rises, or what if the oceans’ p-h balance changes, or what if anthropogenic carbon dioxide is not further regulated by the political types. And the thing that bugs me most is that it is virtually always the politicians rather than actual scientists who discuss it on television.

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