Jason Box spent the summer of 2009 waiting for Greenland’s Petermann Glaciertobreakapart. Everything signaled the glacier
was ready to go. Melt ponds were pooling on its surface, and massive cracks
were opening on the icy tongue that
stretched offshore into Baffin Bay. Box,
a glaciologist at Ohio State University in
Columbus, spent two months on a ship,
his cameras trained on the volatile edge
where ice meets ocean. He was determined to catch Petermann in the act.
As luck would have it, the glacier held
out one more year. When Box wasn’t
looking, on August 4, 2010, a piece of ice
four times the size of Manhattan broke
off. It was the largest iceberg to calve in
the Arctic since 1962.
The world’s frozen places are full of glaciers like Petermann, slow-moving rivers
of ice flowing into the ocean and poised on
the edge between stability and collapse.
In recent years, many of these volatile glaciers have spit out more and more chunks
of ice to float away as icebergs and then
melt. The more icebergs a glacier discharges, the faster it tends to move, thin
and retreat away from the coast.
Scientists say that understanding the
processes that control ice’s march to the
sea, known as “ice dynamics,” is crucial
for understanding the future of the planet’s great ice sheets atop Greenland and
Antarctica. Were it all to melt, there’s
more than enough ice there to raise sea
level by 67 meters.
A complete meltdown isn’t likely, even
centuries from now. But many researchers worry that Greenland and parts of
Antarctica could soon contribute more
to rising sea level, as temperatures are
increasing fastest in those regions. And
a small difference — say a foot of sea
level rise, versus a meter — could mean
the difference between much of Miami
staying above water or going under in the
next century or two.
As ice melts, water trickling through
the remaining ice affects how quickly a
glacier moves and breaks apart. To bet-
ter understand and forecast such effects,
researchers are targeting a few key out-
let glaciers, which funnel ice from the
high frozen interior into the oceans. By
peppering these glaciers with instru-
ments to measure their flow, cameras to
photograph their every move, and even
underwater submersibles to test the sur-
rounding oceans, scientists hope to learn
what drives the ice.
Slip sliding away
Because of ice dynamics, Greenland loses
as much ice each year as is contained in
the entire Alps. Within Greenland, per-
haps no glacier is more responsible for
that ice loss than Jakobshavn Isbrae, on
the island’s west coast. As glaciers go, it’s
one of the world’s fastest, with ice flowing
up to 14 kilometers per year — fast enough
that you can see it move.
How glaciers flow Glaciers are slow-moving rivers of ice, pulled downhill by gravity. If a glacier
meets water, some of the ice breaks off as icebergs. In a stable glacier, this calving of icebergs is
roughly in balance with snowfall. But there are several ways to speed up a glacier, as shown below.
The faster a glacier moves,
the more ice it calves. Likewise,
crumbling edges can speed the
glacier as a whole.
Water can in;ltrate and
melt ice from below;
warmer oceans can speed
The biggest Arctic iceberg in five
decades (circled) broke off Greenland’s
Petermann Glacier on August 4, 2010.
Meltwater on a glacier’s
surface can percolate down
through the ice and lubricate the glacier’s underside,
making the ice slide faster.
March 26, 2011 | SCIENCE NEWS | 23