by many to be the most dangerous lake in Nepal.
“In Peru you could virtually drive to within a
day’s walk of the lake,” he says. In Nepal, “it
could take five, six days to walk to the site from
the nearest roadhead.”
Rolpa Lake is so remote that heavy machinery
had to be helicoptered to the lake in pieces and
then reassembled. After constructing a small
dam with sluice gates, engineers slowly began
releasing water and drawing down the lake. “If
you draw the water down too quickly, it can actu-
ally destabilize the valley flanks, particularly the
lateral moraines that impounded it,” Reynolds
says. Ultimately, the water level of Rolpa Lake
was lowered by more than 11 feet—the first mit-
igation project in the Himalaya.
In 2016 the Nepalese Army participated in an
emergency project that drained Imja Lake by
a similar amount. Neither measure has com-
pletely relieved the respective flood risks, but
both represent, along with the installation of
warning systems, a positive step.
Not all glacial lakes pose an equal threat, and
as scientists continue to develop new ways to
study the lakes, they are learning how to assess
the true level of risk each lake poses. In some
instances, they’ve found that the perceived risk
was overstated, including in the case of Imja
Lake. “There is no actual relationship between
causality of a GLOF and lake size,” Reynolds
says. “What’s critical is how the lake body inter-
acts with the dam itself.”
And it’s not just the large lakes that pose
threats, says Nepali scientist Dhananjay Regmi.
“We are concerned more about big lakes, but most
of the disasters in recent years have been done by
relatively small lakes, which we never suspected.”
Whether the lakes are small or large, there’s
little doubt that conditions for setting off floods
are increasing. Reynolds points out that as the140 NATIONAL GEOGRAPHIC