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of avalanche risk
By Marissa Cevallos
Unless you’re eating breakfast, hearing
snap, crackle and pop may be an early
warning sign of an impending avalanche.
Scientists listening in on icequakes that
rumble through glaciers have developed
a model that can predict a collapse up
to 15 days before it happens, the team
reports in a study posted at arXiv.org.
With that kind of heads-up, villages
could be evacuated and roads closed in
Though all glaciers groan and creak
under stress, glaciers on an incline are
especially creaky, because the top of the
ice is less well supported against the pull
of gravity than the base— like a book
tilted at a 45-degree angle. Accumulating
snow causes more stress. These forces
cause the glacier to fracture, sending tiny
icequakes throughout. Eventually, if a gla-
cier can’t handle the stress, a large chunk
will fall off, pummeling anything below
with a moving mass of snow and ice.
Studies of the Weisshorn peak reveal
that telltale tremors in a glacier can
alert people to an impending avalanche.
hear some small noise before it breaks.”
The team also saw the reflectors accelerate several days before the rupture.
Scientists knew that seismic activity
increases five days before a break-off, but
by combining the motion of the glacier
with the icequake activity, the new model
can detect a rupture 15 days in advance.
“It’s the first time icequakes have been
used as a precursor to these break-offs,”
says glaciologist Fabian Walter of the
Scripps Institution of Oceanography in
La Jolla, Calif.
How a trickle can create a cavern
model of fluid flow helps dissolve puzzle of cave formation
By Alexandra Witze
Spelunkers look at a cave and wonder
how to explore its deepest reaches. But
physicists look at it and wonder how it
got there in the first place. A new math-
ematical analysis solves a long-standing
cave-formation puzzle: how a trickle of
water laced with carbonic acid manages
to quickly dissolve rock to create massive
conduits. The trick, it seems, is that fluid
flow focuses rapidly in certain channels,
which grow at the expense of others and
allow the acid to penetrate deeply.
A new model shows how fluids penetrate rock, forming a cave. At first (left)
channels develop equally, but over time (right) certain channels dominate.
The work could improve understanding of the safety of dams, waste storage
sites or anywhere else fluid might be
seeping through the ground.
Limestone caves form when a tiny
fracture opens in the rock, perhaps due
to some internal stress, and water begins
percolating through. Most water contains some carbon dioxide, making it a
weak acid that can eat away at the calcium carbonate in limestone. It has been
unclear how that dissolution can happen
fast enough to produce deep penetration
and allow long cave systems to form.
The equations describing fluid flow in
the rock always contain a mathematical
instability, the researchers show. That
means that very soon after a fracture
opens, fluid flow focuses along tiny ripples, allowing some channels to expand.
Szymczak says the new work could
help explain why caves sometimes form
faster than expected beneath dams.
From top: bÄw/wikimedia; p. Szymczak, a. Ladd