• What is a debris-covered glacier?

    A glacier where the glacier ice is covered by a layer of sand, gravel, rocks, and boulders. This debris layer ranges from millimetres to several metres thick and changes how the glacier behaves. The surface may resemble a quarry, but underneath the debris there can be hundreds of metres of ice.
  • Where does all the debris come from?

    The debris is mainly sourced from the surrounding mountains during rockfall and avalanche events. When a glacier has thinned considerably, debris can also come from lateral moraine collapse.
  • How does the debris change the glacier ?

    Studies have show that where debris is thin (i.e less than a few centimetres), the darker colour absorbs more solar radiation and increases the melt rate of ice beneath. However, when the debris is thicker it can insulate the ice beneath because less of the thermal energy is able to reach the glacier ice. On glaciers like Khumbu where the debris is over a metre thick over a large area, the highest melt rates occur around ice cliffs and supraglacial ponds, and higher up the glacier where the debris is thinner.
  • If the debris-covered glaciers are melting, why don't they retreat up the valley?

    The debris layer changes how the glacier melts (see above), which means that rather than retreating up the valley, heavily debris-covered glaciers thin. This surface lowering can be up to several metres every year and is clear when seen in relation to the lateral moraines, which mark the past elevation of the glacier.
  • Do debris-covered glaciers still flow?

    Debris-covered glaciers typically have a low surface gradient, which reduces the driving force for ice deformation and flow. On the Khumbu Glacier, the velocity decreases from around 40 metres per year below the icefall, to less than 1 metre per year near the terminus.
  • Why do debris-covered glaciers have lakes on their surface?

    These supraglacial (i.e. surface) lakes or ponds are formed when meltwater accumulates above impermeable ice and sediment beneath. As they warm they melt more ice and can grow larger and ponds can coalesce into a larger lake. Some may persist for several years or even decades. However, they can drain rapidly when they intercept a channel flowing into the glacier.
  • How do melting glaciers affect people?

    It is estimated that glacier fed rivers across the Himalaya provide services such as irrigation, sanitation, and hydropower to a fifth of the world's population. They also provide meltwater during the dry season before the Indian Summer Monsoon. However, many communities live in villages well above the glacier fed rivers because the water often contains too much sediment to be useful and to avoid potential floods. These communities get their water from snow-melt fed mountain streams instead

Email: scott@rockyglaciers.org
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