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It's
HOT!: Garth Llewellyn experiences the
desert heat in Cairo, Egypt.
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Digging in the desert
Geosciences
student Garth Llewellyn once spent three weeks in Egypt
digging for water in the sand—a seemingly futile
task. "The locals say that it last rained for 15
minutes...two years ago," he says.
However,
flooding is a problem for Elizabeth Walters, a Penn
State art historian who is leading the excavation of
Hierakonpolis—one of the most important archaeological
sites for understanding the foundations of ancient Egyptian
society. Water runoff from the irrigation of nearby
sugar cane fields is preventing Walters and her team
from uncovering deeply buried temple ruins.
"The
runoff is ruining the stratigraphy of the site,"
says Llewellyn. "As soon as Elizabeth digs below
the water table, the ground becomes a slurry."
Llewellyn
is part of a team of geoscientists helping Walters figure
out how to "dewater" Hierakonpolis. "Burying
a sump pump in the ground just isn’t economically
feasible," he says, "We’re trying to
characterize the nature of the water flow and find out
if the water table is really rising."
The team of geoscientists—led by Penn State professors
Duff Gold, Richard Parizek, and Shelton Alexander—is
using seismic information to model the groundwater flow
under the archaeological site. Seismic waves move through
different materials, such as sand and water, at different
velocities. The reflection and refraction of the waves
allows researchers to map the water table.
"We found anomalies in the seismic data suggesting
that there was unsaturated sand above and below a pool
of water," says Llewellyn. "That could mean
that a perched water layer is located above the water
table." Perhaps, he explains, the water table is
not permanently rising; rather, it could be rising with
the runoff then falling, leaving a pool of water perched
on an impermeable layer in the ground.
Another
student recorded the seismic data a year before Llewellyn’s
trip to Egypt. When he arrived in the desert in February
2001, Llewellyn’s job was to dig holes and log
the layers of material in the ground: soil, saturated
sand, clay, water, and unsaturated sand.
"In
my undergraduate thesis I’ll compare the seismic
data to the holes to help characterize the area that
showed the seismic anomalies," says Llewellyn.
Garth
Llewellyn is an undergraduate student in the Department
of Geosciences in the College of Earth and Mineral
Sciences at Penn State.
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