This blog provides commentary on interesting geological events occurring around the world in the context of my own work. This work is, broadly, geological fluid dynamics. The events that I highlight here are those that resonate with my professional life and ideas, and my goal is to interpret them in the context of ideas I've developed in my research. The blog does not represent any particular research agenda. It is written on a personal basis and does not seek to represent the University of Illinois, where I am a professor of geology and physics. Enjoy Geology in Motion! I would be glad to be alerted to geologic events of interest to post here! I hope that this blog can provide current event materials that will make geology come alive.

Banner image is by Ludie Cochrane..

Susan Kieffer can be contacted at s1kieffer at gmail.com

Wednesday, August 24, 2011

And, there's no end in sight for the east coast...Hurricane Irene is taking aim

Hurricane Irene from space. NASA
(I'm having difficulty finding photos with times on them.)
UPDATE 8/28/11: CNN.com has reported that 3,000,000 people on the east coast are without power, and that the storm has now begun flooding New York City, which has closed many venues.  Wind speeds are up to 75 miles per hour.

UPDATE 8/29/11: Although the hurricane lost strength because it ran into wind shear as it propagated up the east coast, damage is estimated at up to $10 billion, and President Obama cautions that cleanup from this event will take a long time.

Hurricane, already a Category 3 hurricane, is due to travel up the east coast this weekend.  There is a video from NOAA here that traces its development up to the Category 2 state. At the moment (6:30 p.m. CDT) it has winds of 120 mph, and 200 miles (?) in diameter.

Update on 8/25: If it stays there for awhile, there is an excellent video animation of the progress of the hurricane up to 1:00 CDT here on CNN.com.

Already a huge storm, it is driving a huge amount of water ahead of it, and an excellent article in the Christian Science Monitor today discusses the surge problem.

The term "storm surge" refers to the bulge of water driven by the winds of the hurricane.  There are two sources of this bulge. One is the low pressure in the center of the storm in which atmospheric pressure is reduce and so the sea surface bulges up in response to the lower pressure. This accounts for a few percent of the surge. The vast bulk of the surge results from the large volume of counterclockwise circulating winds that drag the surface water along with them. This circulation puts the greatest surge in the upper-right-hand quadrant of the storm as viewed by satellite. 

8/27/11 Couldn't resist adding this cartoon
by Nate Beeler, The Washington Examiner
Although storm surge is determined, to first order, by the storm's speed, strength, and water depth, the geometry of local features, such as bays, estuaries, and coastal marshes, also matter. If aligned importunely, the surge can be amplified by the local geometry. In this article, for example, he reports that some of the worst surging is projected outside that upper-right-hand-quadrant in Cape Hattaras, at Pamilico Sound, which is on the left side of the track, because the Sound is located where the counterclockwise rotation can spin water down into it after it passes the Cape. It will be interesting to watch the next few days and see how the projections, and their uncertainties, play out.

If this was all that there was to the surge, then it would resemble--on a much longer time-scale--the inexorable onslaught of water that was witnessed when the tsunami came on-shore in Japan.  A steady prolonged rise, followed by a recession as the storm passes.  But that's only part of the story.  Unlike the tsunami, enormous waves ride on top of the bulge, battering like "aquatic sledgehammers." (I really like this writer, Pete Spotts!) This bodes ill for dwellings built on stilts close to the coast.

As was the case with Hurricane Katrina, barrier islands and coastal wetlands would blunt the impact of the waves and surges if they had not been so modified and compromised by development along the coasts.

It is interesting to compare Irene with some previous storms. Here's a link to a post that I did on "super-typhoon Megi" that hit the Philippines in October, 2010, last year. It explains some of the dynamics of these storms. Here is one on Cyclone Yasi that hit Australia in February, 2010. Both of these were larger storms than Irene--the post on Yasi has it superposed on the U.S. that you might find of interest to compare with the image at the left where Irene is superposed on the east coast.  Yasi was huge in comparison.   Cyclone Tracy was fairly small, but caused so much damage in Australia that the song, "Santa Never Made it into Darwin," by Bill Cate and Boyd Robinson that was used as fund-raiser for the reconstruction effort has become legendary in Australia! The post on Tracy has an image of it (very small dot that's easy to miss) compared to Super Typhoon Tip, which is the largest and most intense cyclone on record.
NASA image of Hurricane Irene
on Friday 8/26/11
Irene, on Friday 8/26NAS

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