University in Houston, isn’t so sure all
that sand from Galveston Bay is lost.
Because the researchers didn’t determine the size distribution of grains in
the sand layer, it’s impossible to tell
what proportion of those grains might
be small enough to be bumped back to
shore by normal wave action, even from
waters up to 10 meters deep, he adds.
After looking at historical data, Goff
and his colleagues contend that the
sand is indeed gone for good. An extensive layer of sand dragged offshore
by Hurricane Carla, which struck the
Texas coast in 1961, stayed where the
storm dropped it for at least a quarter
of a century, they note.
Sometimes those layers of storm-shifted sand are buried by quickly
accumulating sediment and thus preserved, leaving in the geological record
a layer known as a “tempestite,” Goff
says. Studying and understanding the
modern-day processes that generate
such layers can aid researchers trying to interpret the geological record.
The presence of a tempestite would
indicate that an area was susceptible
to major storms, for example, and the
size and frequency of such layers within
rock formations could yield clues about
Images taken four days before Hurricane Ike struck (left) and two days after
show erosion along the coast near Galveston, Texas. Arrows denote the same spot.
Because hurricanes strike any given
stretch of coast rather infrequently,
data on the storms’ effects are hard to
come by. On the broader scale, satellite observations give scientists a look
at the speed and direction of currents
that hurricanes generate at the ocean’s
surface, says oceanographer William J.
Teague of the Naval Research Laboratory at NASA’s Stennis Space Center in
Mississippi. “But once you get below the
surface, there’s a void of data,” he notes.
While buoys far off the Texas coast
were blown or dragged southwest as far
as 35 kilometers during Ike, researchers don’t know how strong the storm-induced currents were, when the buoys
Hidden destruction ike’s winds forced a 5-meter storm surge
into galveston bay. much of that water rushed back to sea through the
bolivar roads inlet (below, arrow). the flow’s force took the tops off
shell-and-gravel ridges and dumped new deposits on the inlet floor
(sonar images on right show area in red box on map).
moved or what path they took — it’s clear
only where the buoys ended up. But new
analyses of data collected by seafloor
instruments during another hurricane,
2004’s Ivan, could let researchers make
some reasonable guesses about water’s
scouring power beneath the surface.
Just before Ivan slammed into the
Gulf Coast, it passed directly over an
array of seafloor sensors deployed in
mid-depth waters on the continental
shelf south of Mobile, Ala. At that time,
Ivan was a category 4 hurricane creeping
northward at about 20 km/hr, Teague
says. Previously, his team’s analysis of
data gathered during the event revealed
the largest waves ever measured by
instruments (SN: 6/11/05, p. 382). Now,
top: usgs; bottom left: map: usgs, adapted by t. dubÉ; map inset: atlas/map resources; bottom right: j. goff et al/geology 2010