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Posted at 11:15 AM ET, 07/22/2010

Did melting ice cause D.C. earthquake?

By Steve Tracton

* Heat Advisory Fri.: Full Forecast | Heat & humidity double whammy *
* Tropical Depression 3 forms: Hurricane Tracking Center *


Current sea-Level trends with arrows representing the direction and magnitude (mm/yr) of change. Credit: NOAA.

The news rang out across the nation: Mild earthquake shakes D.C. area. A real earthquake it was -- not the rumblings so often emanating from "inside-the-Beltway" political battles. Although the largest earthquake in the area since tracking of such began in 1974, it was minor in intensity (3.6 on the Richter scale) and no injuries or damage were reported.

But, could there be more to this? I ask in the context of two other recent noteworthy items. The first concerns a story on the disappearance of beaches along the Eastern seaboard, "Buh-bye East Coast Beaches." As the article notes, once popular day trips from Washington to Chesapeake Beach, Md., lead now not to wide sandy beaches, but rather to "a seven-foot-high wall of boulders protecting a strip of pricey homes marked with 'No Trespassing' signs." The second item concerns the breakup and retreat of one of the largest glaciers in Greenland. Water from melting glaciers contribute to rising sea levels, and thereby could enhance the threat to beaches on the East coast and elsewhere.

But what, you might ask, does the earthquake have to do with any of this? The short answer, perhaps surprisingly, is just what the other two items have in common -- sea-level change.

The primary contributors to sea level rise are generally believed to be thermal expansion of warming oceans and addition of water to oceans from melting glaciers and ice caps atop Greenland and Antarctica. However, local changes in sea level are relative the land such that, if the land subsides, sea level rises even if there is no additional water. In fact, the land is subsiding along the East Coast, and this might very well be tied to earthquakes such as the one just experienced.

At the end of the last ice age, when the massive ices sheets that once covered much of North America retreated, removal of the weight that had been depressing the underlying land surface led to a slow -- and still ongoing -- rising of the land. More directly relevant is that regions outside the periphery of the ice sheet, which includes much of the U.S. East Cost, have responded in an opposite manner -- these lands have been sinking.

According to environmental scientists at the University of Pennsylvania, sea level along the Atlantic Coast is rising faster now than at any time in the past 4,000 years, largely due to land being lost under the waves due to post ice-age subsidence. Additionally, the researchers find that the mid-Atlantic coastlines of New Jersey, Delaware and Maryland are subsiding twice as much as areas to the north and south. Hence, these regions are subject to an increased threat of further beach erosion, wetlands converting to open water, and coastal flooding. (Note: where the earth continues to rebound, most notably in Alaska, sea level relative to land is actually falling).

It's well known that, while major earthquakes are rare, mild earthquakes are not especially out of the ordinary along the Eastern seaboard. Mark D. Petersen, a seismologist with the USGS, says the ancient rock underlying this part of the country is riven with fissures and faults. On the other hand, according to the USGS, known faults east of the Rockies seem to have nothing to do with modern earthquakes. "It's just part of the ongoing creaking and grinding of the stable part of the continent," said Scott Southworth, a USGS scientist in Virginia, of the local quake last week.

Bottom line: exactly what geological factors caused last week's quake, and earlier (and likely future) ones, is unclear. Nevertheless, it's certainly possible that earthquakes along the East Coast are tied to the continuing subsidence of land following the last ice age. However, they occur too infrequently to firmly establish whether this or any alternative mechanism explains the quakes with certainty.

Independent of the explanation for the quakes, it's important to take account of the rise and fall of land masses when considering the question of sea-level rise associated with climate change. As reported by the bulletin of the American Congress on Surveying and Mapping (ACSM), sea level has been rising at the rate of about 3 mm/yr -- a rate nearly twice the 20th century average. Further, based on long-term observations by NOAA, the rate of sea-level rise due to regional subsidence of the coastal plain of mid-Atlantic states is 3 to 5 mm/yr. It follows that localized land subsidence, possibly linked to earthquakes, can considerably magnify sea-level rise resulting from climate change.

Postscript: According to scientists at the University of Miami, just as the underlying land rebounded as the ice age glaciers retreated, Greenland is rising as the Greenland ice sheet melts and glaciers over land are shed into the sea. The uplift apparently started in the late 90s with some coastal areas rising by nearly one inch per year (I'm unaware of any information concerning subsidence on or around the periphery of Greenland). The report goes on to state that, "what's surprising, and a bit worrisome, is that the ice is melting so fast that we can actually see the land uplift in response. Even more surprising, the rise seems to be accelerating, implying that melting is accelerating."

By Steve Tracton  | July 22, 2010; 11:15 AM ET
Categories:  Climate Change, Environment, Tracton  
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Comments

Great piece! Love the geomorphology references.

Posted by: ennepe68 | July 22, 2010 12:05 PM | Report abuse

It's also possible that rising sea levels may enhance stresses on long-dormant faults, reactivating them.

In addition, the sudden stress induced by the day-after Christmas major earthquake/tsunami of some years back may be translating chain-reaction adjustments along faults from Sumatra onwards throughout the entire plate/fault system...thus the Haiti quake could be a delayed reaction to the big quake of some years back. Could we have another New Madrid or San Andreas "big one" in our future?

Posted by: Bombo47jea | July 22, 2010 12:52 PM | Report abuse

Wonderful... so now I have to be vigilant against earthquakes in addition to giant snakes.

Posted by: spgass1 | July 22, 2010 2:31 PM | Report abuse

My wife got some pics of one climbing up our screen door... not giant, but a good four feet or so...

Posted by: spgass1 | July 22, 2010 4:18 PM | Report abuse

Speculative and not likely. If this quake had instead happened on the New Madrid fault we would not make any association with sea level. We happened to have it here on our old fault. The likelihood of earthquakes has no relation to sea level changes in general as seen from the quake maps here:

http://www.mgs.md.gov/esic/brochures/earthquake.html

compared to the uplift map in the posting.

Posted by: eric654 | July 22, 2010 5:41 PM | Report abuse

eric654

Experts tell me that one cannot say that the subsidence is responsible for the level of seismic activity in this region, but neither do they dismiss the possibility of a connection.

It is not unreasonable to hypothesize that the subsiding earth might shift the rock along or independent of faults with the consequent creaking and grinding triggering earthquakes such as the one last week.

How likely remains an open question. It's proper to be skeptical (as am I), but the quake maps you refer to are nsufficient to disprove the hypothesis.

Posted by: SteveT-CapitalWeatherGang | July 22, 2010 7:24 PM | Report abuse

Anyone can speculate on climate change being linked to anything, and the good ministers of propaganda at the Capital Warmist Gang will tell you that you can't prove its not.

Show me any scientific evidence linking temperature to earthquakes, I dare you.

Posted by: ecocampaigner | July 22, 2010 8:08 PM | Report abuse

Steve, I prefer complete theories that explain all earthquakes, not just some. I realize there are multiple factors but the theory should include them. To then use the phrasing "cause and effect" or "resulting in" implies much more than that.

Another reason to discount sea level now is the rise from the LIA is trivial (20 cm) compared to the rise from the ice age 11k years ago (120 m) and there are no prehistorical studies that I found that mention that much larger sea level rise (they talk about faults with crustal slippage and subsidence as a result not a cause of earthquakes).

Posted by: eric654 | July 22, 2010 8:34 PM | Report abuse

The use of science in the climate change field seems to be minimal as it is. They have no problem throwing out all sorts of unsubstantiated theories and "studies". Earthquakes, hurricanes, tornadoes, drought, floods, cold, heat, blizzrds, ice forming, ice melting, landslides, fires all due to climate change. I think the majority of people know with their gut this is all junk science.

Posted by: Tom8 | July 22, 2010 9:27 PM | Report abuse

Thanks for this, Steve. Interesting angle to think about.

Posted by: Ann-CapitalWeatherGang | July 22, 2010 10:09 PM | Report abuse

Tom8, did I see a baby floating by in the bathwater? The nice thing about this forum is that there are lots of weather people who understand that ice forms in the winter and melts in the summer. Sometimes a bit or a bit less forms or melts and interesting theories can be entertained. But I think it is worth drilling down into detail each time to explore the merits. There is usually an influence of something on something else even if it is very small. In fact we could argue that everything in the universe affects everything else even if it is a minute amount of gravity or a photon or two.

Posted by: eric654 | July 23, 2010 6:19 AM | Report abuse

Does it bother anyone that there were no glaciers over Washington? Does it matter to anyone that there is no coorelation between temperature and earthquakes? Does it matter to anyone that minor earthquakes along the eastern seaboard are common?

When will the Washington Post replace the Capital Warmist Gang with people who focus on the weather and not on a radical liberal political agenda?

Posted by: ecocampaigner | July 23, 2010 11:57 AM | Report abuse

ecocampaigner wrote, "... the Capital Warmist Gang ..."

Good one!

Mr. Q.

Posted by: Mr_Q | July 23, 2010 1:17 PM | Report abuse

The comments to this entry are closed.

 
 
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