question: How are glaciers constantly moving and what causes it?
comment: Ice is not perfectly solid, it can flow like very very thick molasses. But what's pushing it? Gravity. If snow packs up to form a thick pile of ice on the side of a mountain, it will flow downhill. Even without a mountain, a large enough pile of ice will sag and flow under its own weight.
passages: Section::::Mass balance research worldwide.
   Section::::Mass balance research worldwide.:Norway mass balance program.
   Section::::Mass balance research worldwide.:Alaska.
   Section::::Mass balance research worldwide.:New Zealand.
   Section::::Mass balance research worldwide.:Sweden Storglaciären.
   Section::::Mass balance research worldwide.:Austrian Glacier Mass Balance.
   Section::::Mass balance research worldwide.:United States Geological Survey (USGS).
   Section::::Mass balance research worldwide.:Iceland Glacier mass balance.
   Glaciers grow and shrink due both to natural variability and external forcings. Variability in temperature, precipitation, and englacial and subglacial hydrology can strongly determine the evolution of a glacier in a particular season. Therefore, one must average over a decadal or longer time-scale and/or over many individual glaciers to smooth out the local short-term variability and obtain a glacier history that is related to climate.
   Section::::Glaciers.
   Section::::Key areas of operation.:Agriculture.
   Section::::Mass balance research worldwide.:Swiss mass balance program.
   Section::::Glaciers by continent.
  
  Section::::Glaciers by continent.:Africa.
  
  Africa, specifically East Africa, has contained glacial regions, possibly as far back as the last glacier maximum 10 to 15 thousand years ago. Seasonal snow does exist on the highest peaks of East Africa as well as in the Drakensberg Range of South Africa, the Stormberg Mountains, and the Atlas Mountains in Morocco. Currently, the only remaining glaciers on the continent exist on Mount Kilimanjaro, Mount Kenya, and the Rwenzori.
  
  Section::::Glaciers by continent.:Antarctica.
   Glaciers form where the accumulation of snow and ice exceeds ablation. A glacier usually originates from a landform called 'cirque' (or corrie or cwm) – a typically armchair-shaped geological feature (such as a depression between mountains enclosed by arêtes) – which collects and compresses through gravity the snow that falls into it. This snow collects and is compacted by the weight of the snow falling above it, forming névé. Further crushing of the individual snowflakes and squeezing the air from the snow turns it into "glacial ice". This glacial ice will fill the cirque until it "overflows" through a geological weakness or vacancy, such as the gap between two mountains. When the mass of snow and ice is sufficiently thick, it begins to move due to a combination of surface slope, gravity and pressure. On steeper slopes, this can occur with as little as 15 m (50 ft) of snow-ice.
   Section::::Mass balance research worldwide.:Geological Survey of Canada-Glaciology Section (GSC).
   Since glacial mass is affected by long-term climatic changes, e.g., precipitation, mean temperature, and cloud cover, glacial mass changes are considered among the most sensitive indicators of climate change and are a major source of variations in sea level.
   The health of a glacier is usually assessed by determining the glacier mass balance or observing terminus behavior. Healthy glaciers have large accumulation zones, more than 60% of their area snowcovered at the end of the melt season, and a terminus with vigorous flow.
  
  Following the Little Ice Age's end around 1850, glaciers around the Earth have retreated substantially. A slight cooling led to the advance of many alpine glaciers between 1950 and 1985, but since 1985 glacier retreat and mass loss has become larger and increasingly ubiquitous.
  
  Section::::Motion.
   Section::::Polar regions.
  
  Despite their proximity and importance to human populations, the mountain and valley glaciers of tropical and mid-latitude glaciers amount to only a small fraction of glacial ice on the Earth. About 99 percent of all freshwater ice is in the great ice sheets of polar and subpolar Antarctica and Greenland. These continuous continental-scale ice sheets, or more in thickness, cap much of the polar and subpolar land masses. Like rivers flowing from an enormous lake, numerous outlet glaciers transport ice from the margins of the ice sheet to the ocean.
  
  Section::::Polar regions.:Iceland.
   Section::::Geography.
   Section::::Unconstrained Glaciers.:Ice Streams.
   Section::::Unconstrained Glaciers.:Ice sheets and Ice Caps.:Ice Caps.
   Section::::Glaciers.
   In addition to the dry, unglaciated polar regions, some mountains and volcanoes in Bolivia, Chile and Argentina are high () and cold, but the relative lack of precipitation prevents snow from accumulating into glaciers. This is because these peaks are located near or in the hyperarid Atacama Desert.
  
  Section::::Glacial geology.
  
  Glaciers erode terrain through two principal processes: abrasion and plucking.
   The word "glacier" is a loanword from French and goes back, via Franco-Provençal, to the Vulgar Latin ', derived from the Late Latin ', and ultimately Latin "", meaning "ice". The processes and features caused by or related to glaciers are referred to as glacial. The process of glacier establishment, growth and flow is called glaciation. The corresponding area of study is called glaciology. Glaciers are important components of the global cryosphere.
  
  Section::::Types.
  
  Section::::Types.:Classification by size, shape and behavior.
   Glacial surges in Karakoram occur in the presence of "extreme uplift and denudation."
  