Spiky Glaciers Are Slower to Melt

Trying to save high-altitude glaciers? Then sprinkle them with dirt, say researchers, to increase the formation of ice spikes that shade large areas on the glaciers, slowing their melting.

Meredith Betterton of the University of Colorado at Boulder, US, and colleagues in France have been sprouting ice spikes in a lab freezer. They say the spikes mimic those found on mountain glaciers, notably above 4000 metres in the Andes. The real spikes can be up to 5 m high and are known as "penitentes" because they resemble precessions of white-hooded monks.

Betterton's replicas, however, are only a few centimetres high. She created them by putting blocks of snow in a freezer with a transparent lid and shining a spotlight onto them, mimicking sunlight. Within a few hours, sublimation of the snow had left spikes up to 5 centimetres high protruding from the surface (see image, top right).

When Charles Darwin first noticed penitentes while travelling through Chile, he noted that locals believed they were formed by strong winds. Betterton's lab experiments confirm what she had previously suggested after computer modelling: that sunlight forms the spikes independently of wind.