----- forwarded message -----
Date: Thu, 22 Jul 2004 16:49:35 -0600
From: Teresa Binstock <[EMAIL PROTECTED]>
Subject: Scientists make breathtaking discovery at the beach - Mother Earth breathes!
Scientists make breathtaking discovery at the beach
Wednesday, July 21, 2004
By RANDOLPH E. SCHMID
THE ASSOCIATED PRESS
http://seattlepi.nwsource.com/national/182904_breathing21.html
WASHINGTON -- The millions of Americans enjoying beach vacations this
summer may not be aware of it, but the land beneath their feet is breathing.
As tides come and go, the water causes changes in underground air
pressure, forcing air and moisture in and out of the ground along the
shore, Jui Jiao of the University of Hong Kong found in studying coastal
areas near his school.
While tidal changes in underground water levels along the shore were
known, changes in air pressure beneath the surface were not as well
recognized, Jiao reports in Geophysical Research Letters.
The inhaling and exhaling isn't something likely to be noticed by
frolicking beachgoers, though Jiao believes organisms living in the soil
should be able to detect it.
"People can feel the process only under very special conditions. In Hong
Kong, people once saw the water bubbles coming out of the fractures or
joints of an asphalt pavement and heard the noise of the air flow
through fractures," he said.
But that was a special case with a rapidly changing tide and air and
water moving through a limited number of underground pathways.
"Under normal conditions, people usually cannot directly detect this
phenomenon. This is probably a reason why this phenomenon has not been
studied until recently."
Jiao said the breathing causes a constant exchange of air, water
moisture and any pollution that may be present between the soil and the
air. In addition, the constant changes in pressure beneath the surface
may have an effect on buildings, airport and seaport structures and
coastal highways, which are usually designed to support downward acting
loads.
Since asphalt and building structures can block this air flow, the
coastal breathing may produce repeated cyclical -- up and down --
pressures on these structures.
"It is well known that the strength of materials under cyclic conditions
is significantly lower than for (single direction) loading," Jiao said
via e-mail. "The performance of concrete or asphalt surface under cyclic
loading by tidal-induced air pressure below the paved ground surface
needs to be evaluated."
Douglas Inman of the Scripps Institution of Oceanography in La Jolla,
Calif., agreed that the finding "will be very important to coastal
engineers working in areas of reclaimed land where it is important to
avoid having roads and structures pop up."
Inman, who was not part of Jiao's research team, said that the breathing
may be more common in areas of artificial fill, such as Hong Kong.
Jiao and his co-author, Hailong Li of the China University of
Geosciences at Wuhai, found that regular changes in below-ground air
pressure were most affected by the rising and lowering of the water
table with the tides.
The process, which is lessened when it is raining, is relevant to
coastal areas worldwide, Jiao said.
The research was financed by the Hong Kong Research Grants Council, the
University of Hong Kong and the National Science Foundation of China.
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