Multispectral image analysis of glaciers and glacier lakes in the Chugach Mountains, Alaska

Abstract

The Chugach Mountains contain the largest nonpolar alpine glaciers in the world and include a wide variety of glacier types: some are land terminating; some calve variously into tidewater, lakes, and rivers; some are heavily debris covered; some are surge-type, whereas others are neither debris covered nor surge type. Nearly all are retreating, thinning, or both, though some rare ones are advancing, and some are thickening at high elevations. To assist the further documentation of changes, we establish an inventory of glaciers in the eastern Chugach Mountains. Several case studies of diverse glacier types showcase remotesensing applications and are used to derive new knowledge of their current states and dynamical behavior. Several of these glaciers currently discharge into the Copper River and can be used to understand the processes governing glacier damming of large rivers. The Copper River, along with other major valley outlets from the Copper River Basin, was dammed several times by ice during the Pleistocene, forming a lake 10,000–20,000 km2 in area, called Glacial Lake Ahtna. Insights from the modern Childs, Miles, and Allen Glaciers—each of which fronts the Copper River—show that damming is not easily accomplished; direct encroachment, complete crossing, and successful damming require very low river discharge and probably introduction of abundant rock debris from a landslide onto the glacier. The last century has involved degradation of the Little Ice Age piedmont lobes of many valley glaciers in the Chugach Mountains and especially its Copper River corridor. These glaciers are generally losing over a meter per year of surface elevation. In another chapter highlight, we have found that crenulation and chevron folding of medial moraines does not require surging, as is commonly assumed; rather, the deformation can occur by flow diversion, without any surge activity, into ice-marginal lakes—a process we term a glacial aneurysm.