Rock debris can protect glaciers from climate change

According to new evidence, rock debris that lie on top of glacier formations may protect them from climate change and slow down their melting pace.

A new study that evaluates the state of rock debris covering Earth’s glaciers, was published in Nature Geoscience on August 3, 2020.

Rock debris refers to the remains of certain geological processes that take place on the Earth's crust (e.g. erosion, rockslides, rockfalls, volcanic explosions and lava eruptions). The new research estimates the percentage of the Earth's glaciers that are covered with debris and incorporates their impact on the existing prediction models regarding glacier melting.

Debris accumulation in glaciers occurs when the ice sheets melt and the formations shrink, revealing the rocky slopes which become vulnerable to erosion and sliding. As a result, rock fragments are gathered on top of glacier surfaces and create a protective layer that can be very thick.

What is really interesting about this phenomenon is that these layers were never mapped before and therefore, their impact was not taken into consideration in prediction models about glacier meltdowns and seawater level rise.

Scientists from Northumbria University utilized satellite imagery to derive the debris cover over Earth's glaciers. By studying an area of about 923,000 km² of glaciers, they found out that 20% of them have a substantial percentage of debris cover.

Moreover, the team managed to map the current state of glaciers, updating the Randolph Glacier Inventory, a collection of digital outlines of glaciers, which has been widely utilized in numerous studies. Scientists also found certain errors (3.3%) in the inventory which they corrected.

According to Dr. Sam Herreid, lead author of the study and a glaciologist who conducted the research as part of his Ph.D., incorporating the debris impact in forecast models is of high importance. Otherwise, it is almost certain that the glacier meltdown process and the seawater level rise will be overestimated.

“We now know that debris cover is present on almost half of Earth’s glaciers, with 7.3% of the world’s total mountain glacier area being debris covered. When we consider that much of this debris cover is located at the terminus, or toe, of a glacier where melt would usually be at its highest, this percentage becomes particularly important with respect to predicting future water resources and sea level rise,” Dr. Herreid, stated.

The authors assessed data for each case study and compared young (in Greenland) with older (in the Himalayas) glaciers. By deriving their future evolution process, they found out that a great proportion of Earth's glaciers are on their old stages and are currently declining, a fact that can be associated with climate change. “We found that the bulk of glaciers that have a debris cover today are beyond a peak debris cover formation state and are trending closer to the 'old' Himalayan glaciers that might not be around for much longer," Dr. Francesca Pellicciotti, co-author of the study and Associate Professor at Northumbria University, added.