<i>Taking the pulse of a Himalayan glacier</i>

Ngozumpa Glacier in Nepal snakes away from the sixth highest mountain in the world, Cho Oyo.
It's not the greatest glacier to look at - far from it. It's smothered in a layer of rocky debris that's fallen from the surrounding cliffs, giving it a very grey, dirty appearance.
But Ngozumpa is generating a lot of scientific interest at the moment.
The Nepalese Himalayas have been warming significantly more than the global mean temperature in recent decades.
Glaciers in much of the region are showing signs of shrinking, thinning, and retreating; and this is producing a lot of melt water.
On Ngozumpa, some of this water is seen to pool on the surface and then drain away via a series of streams and caverns to the snout of the glacier.
There, some 25km from the mountain, an enormous lake is growing behind a mound of dumped rock fragments.
This lake, called Spillway, has the potential to be about 6km long, 1km wide and 100m deep.
The concern is that this great mass of water could eventually breach the debris dam and hurtle down the valley, sweeping away the Sherpa villages in its path. The threat is not immediate, but it's a situation that needs monitoring, say scientists.
One of the researchers at work on Ngozumpa is Ulyana Horodyskyj, from the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado in Boulder, US.
She is setting up remote cameras to monitor the surface, or supraglacial, pools of water that dot the length of Ngozumpa. Some are small; some are big - the size of several football fields.
Already, she has been able to establish just how dynamic these water features can be as they drain and fill in rapid time.
The volumes involved can be prodigious. In one event, her cameras spied a supraglacial lake losing more than 100,000 cubic metres of water in just two days. Within five days, the lake had recovered half the volume, fed by waters from higher up the glacier.