Guest essay by Eric Worrall
The Australian ABC has published details of a new climate scare – the possibility that global warming will lubricate the worlds glaciers with meltwater, causing them to speed up, accelerating abrasive erosion.
According to the ABC;
Climate change may cause ‘substantial increase’ in erosion as glaciers speed up
Faster-moving glaciers carve away more of the landscape than their slower-moving counterparts, according to a new study of a New Zealand glacier.
The findings, reported in the journal Science, have significant implications for glacial erosion as Earth gets warmer due to climate change.
“The glaciers will accelerate and the rate of glacial erosion will increase substantially,” said one of the study’s authors, Dr Simon Cox of the Institute of Geological and Nuclear Survey Science in Dunedin, New Zealand.
“So we end up with more rapid carving of our landscape by glaciers and a corresponding increase in the levels of sediment and mud that are carried out in alpine streams and rivers towards the sea.”
Dr Cox and his colleagues spent five months in 2013 and 2014 studying the Franz Josef Glacier in New Zealand’s Southern Alps.
The authors found erosion to be highly sensitive to small variations in the slope of the glacier, the hardness of the rocks over which the glacier is moving, and the amount of rain the region receives.
The abstract of the study;
Assessing the impact of glaciation on Earth’s surface requires understanding glacial erosion processes. Developing erosion theories is challenging because of the complex nature of the erosion processes and the difficulty of examining the ice/bedrock interface of contemporary glaciers. We demonstrate that the glacial erosion rate is proportional to the ice-sliding velocity squared, by quantifying spatial variations in ice-sliding velocity and the erosion rate of a fast-flowing Alpine glacier. The nonlinear behavior implies a high erosion sensitivity to small variations in topographic slope and precipitation. A nonlinear rate law suggests that abrasion may dominate over other erosion processes in fast-flowing glaciers. It may also explain the wide range of observed glacial erosion rates and, in part, the impact of glaciation on mountainous landscapes during the past few million years.
So how bad is this erosion?
… We designed this study to specifically constrain how glacial erosion relates to ice-sliding velocity. We simultaneously quantified erosion rates and sliding velocity during a 5-month period, from November 2013 to April 2014, over the entire Franz Josef Glacier, New Zealand. This glacier exhibits surface velocities that are largely dominated by high sliding velocities on the bedrock (22), up to about 3 m/day. We measured these high velocities accurately from remote sensing and expected to find large erosion rates. The analysis of continuous suspended sediment load indicated very high erosion rates (about 10 mm/year), whereas glacial sediment production remained lower than the transport capacity of the glacial system (23). We also found that the glacial sediments come predominantly from under the glacier, based on the mineralogy, fossil organic carbon, and the very low fraction of modern organic carbon found in the glacial stream (23). These observations imply that sediments collected at the glacier front can be used to constrain the glacial erosion law. …
Even if erosion does accelerate, I suspect we’ll have enough time to prepare, for the consequences of erosion rates of 10mm / year, in mostly uninhabited, inhospitable regions of the world.