Dynamic Planet * Glacial Formation * when snow remains in the same area year-round, where enough snow accumulates to transform into ice * Each year, new layers of snow bury and compress the previous layers * This compression forces the snow to re-crystallize, forming grains similar in size and shape to grains of sugar. * Gradually the grains grow larger and the air pockets between the grains get smaller, causing the snow to slowly compact and increase in density. * After about two winters, the snow turns into firn—an intermediate state between snow and glacier ice. At this point, it is about half as dense as water. * Over time, larger ice crystals become so compressed that any air pockets between them are very tiny. In very old glacier ice, crystals can reach several inches in length. For most glaciers, this process takes over a hundred years. * Mass-Balance * Ablation zone- more snow falls in winter * Accumulation zone-where snow and ice melt * Equilibrium line- separates these two places * Mass-balance- balance between ablation and accumulation * Studying this can help us study climate change * Short, low elevation, or south facing glaciers respond quicker * Warmer temperatures- smaller and thinner * Moraines- mark maximum extent during cooler periods * Lower temperatures- increasing mass * Movement * Weight of a thick layer of ice + it deforms as a "plastic" material, combined with gravity's influence, * Internal deformation- individual ice crystals within a glacier deform and slide across one another * Basal sliding- water = lube * glaciers to flow very slowly * Ice may flow down mountain valleys; fan across plains, or in some locations, spread out to the sea. * Movement along the underside of a glacier is slower than movement at the top due to the friction created as it slides along the ground's surface * Terminus- the lowest end of a glacier; also called glacier snout or toe. * Ablation-combined processes which remove snow or ice from the surface of a glacier or from a snow-field * Quantity lost by these processes * Reduction of the water equivalent * Accumulation-all processes by which snow or ice are added to a glacier, this is typically the accumulation of snow, which is slowly transformed into ice; other accumulation processes can include avalanches, wind-deposited snow, and the freezing of rain within the snow pack. * Types of Flow * Retreat-when a mountain glacier's terminus doesn't extend as far down valley as it previously did; * Occurs when ablation surpasses accumulation. * glacier still deforms and moves down slope, like a conveyor belt * Advance-when a mountain glacier's terminus extends farther down valley than before; glacial advance occurs when a glacier flows down valley faster than the rate of ablation at its terminus. * Usually very slow and takes a long time to notice difference * Sometimes very fast and can be seen within weeks and months * Surge- racing forward at several meters/day for weeks and months * Glacier Types * Ice Sheet- Found only in Antarctica and Greenland, ice sheets are enormous continental masses of glacial ice and snow expanding over 50,000 square kilometers * Ice Shelves- extend over the sea, and float on the water * surround most of the Antarctic continent * Retreating ice shelves may provide indications of climate change. * Ice Caps- miniature ice sheets, relatively flat and high in elevation * Ice Streams and Outlet Glaciers- channelized glaciers that flow more rapidly than the surrounding body of ice. For instance, the Antarctic ice sheet has many ice streams flowing outward * Ice Fields-similar to ice caps, except that their