365 Days of Climate Awareness 54 - Alpine Glaciers

Mountains are a natural home to snow and ice, as the air temperature cools roughly 10°C every thousand meters (15°F every half mile) of elevation, so conditions are frequently ripe for accumulation of snow and ice. So alpine, or sometimes cirque (named for their semicircular headwalls) glaciers form at elevation and flow down the mountainsides. In colder climates several alpine glaciers might join into a larger continental ice flow, though now, most alpine glaciers around the world are in retreat.

Alpine glacier (note medial moraines).

Due to the frequently extreme slopes where these glaciers are located, they begin flowing when much thinner than flatland (continental) glaciers, with thicknesses as low as 5 meters. In addition, the combined influence of ice and gravity lead to high rates of erosion from the mountainside. Glaciers create very distinctive erosional forms on mountains, including deep, narrow valleys and the tall, thin ridges between them called arêtes. The rock which comes from the arêtes gathers into bands within the glacier and, especially where two valley glaciers join into one stream, form medial moraines, large streams of rock and sediment transported in a rough line along with the rest of the glacier.

Diagram of an alpine glacier.

Perhaps the most unique and striking geological product of mountain glaciers is the horn, a mountain peak shaved down, frequently into a rough quadrilateral pyramid, by repeated cycles of glaciation. Probably the world's most iconic example is the Matterhorn in Switzerland, but if you're in any cold alpine region, and you look around, chances are you'll see at least a few. The honed edges and flattish surface between them are excellent evidence of past glacial activity.

Perhaps the world's most famous mountain peak.

Alpine glaciers are an important bellwether for global climate change, as they are sensitive to a number of factors including mean temperature, precipitation and even pollution (which affects their albedo). As a fleeting glance ahead--and why I'm spending as much time as I'm going to on the cryosphere--the cold regions of the planet, as a whole, are a good gauge as to the progress of global warming. Where the differences in the tropics are not always apparent, since they're very warm already, small differences have outsize effects where it's cold.

Tomorrow: continental glaciers.

Be well!