Digging a snowpit onTaku Glacier, in Alaska to measure snowpack depth and density
Snowpack is an accumulation ofsnow that compresses with time and melts seasonally, often at high elevation or high latitude.[1][2] Snowpacks are an important water resource that feed streams and rivers as they melt, sometimes leading to flooding. Snowpacks provide water to down-slope communities for drinking and agriculture.[3] High-latitude or high-elevation snowpacks contribute mass toglaciers in theiraccumulation zones, where annual snow deposition exceeds annual melting.[4]
Assessing the formation and stability of snowpacks is important in the study and prediction ofavalanches.[5][6] Scientists study the physical properties of snow under different conditions and their evolution, and more specifically snowmetamorphism,[7][8] snowhydrology (that is, the contribution of snow melt tocatchment hydrology), the evolution of snow cover withclimate change and its effect on theice–albedo feedback and hydrology, both on the ground and by usingremote sensing.[9] Snow is also studied in a more global context of impact on animalhabitats andplant succession.[10] An important effort is put into snow classification, both as ahydrometeor[11] and on the ground.[12]
Snowpack modeling is done for snow stability, flood forecasting, water resource management, and climate studies.[13] Snowpack modeling is either done by simple, statistical methods such asdegree day or complex, physically based energy balance models such as SNOWPACK, CROCUS or SNOWMODEL.[14][15][16]
Maritime snowpacks typically feature very deep snow as seen at this creek inWashingtonLess snow is typical for continental snowpacks.Loveland Pass, Colorado
The three main types of snowpack are maritime, intermountain, and continental.
Maritime snowpacks are typically found on the windward side of continents, near oceans. They usually feature warmer winter temperatures that stay around freezing (−5 to 5 °C (20 to 40 °F)) and more precipitation, leading to a snowpack that is over 3 metres (10 ft) deep. Frequent storms deposit snow with a higher snow-water equivalent, often around 10 to 20 percent moisture. Most avalanches occur during or immediately after storms, as weak layers do not persist with warmer temperatures and frequent midwinter rain.[17] Thus, it is typical to ski steep, avalanche prone terrain as soon as 24 to 36 hours after the storm.[18] Many areas with a maritime snowpack receive 15 to 25 metres (49 to 82 ft) of annual snowfall. Areas with a typically maritime snowpack include theCascade Range,Coastal Range, western Norway,[19] and theSierra Nevada.[18]
Intermountain[20] or transitional[19] snowpack is colder and drier than maritime snowpack, usually around 1.5 to 3 metres (5 to 10 ft) deep. Temperatures stay colder than maritime climates but warmer than continental climates, around −15 to 3 °C (5 to 40 °F). Although intermountain snowpacks can feature persistent weak layers, avalanches also occur within storm snow. Unlike in maritime climates, instability lingers for several days to weeks after storms.[20] Typical areas for this snowpack include theWasatch Range,Selkirks, and parts of theAlps.[21]
Continental snowpacks are the coldest and thinnest, featuring snow less than 1.5 metres (5 ft) deep and winter temperatures under −10 °C (10 °F). Storms are less frequent and deposit less snow, which is less dense. Faceted snow and depth hoar is the typical weak layer, often covered by hard wind slabs. The instability is very persistent and often leads to higher rates of avalanche fatalities.[22] Areas with a typically continental snowpack includeColorado, theCanadian Rockies, theBrooks Range, and thePamir Mountains. Because of the persistence of weak layers, forecasting relies much more heavily on snowpit tests to determine stability.[19] In continental climates, avalanches can start on less steep slopes than in intermountain or maritime climates.[23]
Local and regional weather conditions can change the type of snowpack typical for a region, for example a typically maritime region might have a cold and thin early season snowpack that resembles continental type, while even a few feet apart the snowpack depth can vary enough to produce vastly different conditions.[24] Elevation also dramatically affects the type of avalanches typically experienced in a particular area.[21]
Snowpack can affect ecological interactions inboreal andmontane forests. In theinland rainforests ofBritish Columbia, for example, deep snowpacks liftcaribou into the lower treecanopy while also catching large amounts of fallen "hair"lichens such asBryoria andAlectoria. These accumulations provide a dependable winter food supply for the endangered deep-snow mountaincaribou, a process researchers have termed the "manna effect".[25]
^Mousavi, Seyedmohammad (2016). "Dry snowpack and freshwater icepack remote sensing using wideband Autocorrelation radiometry".2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS). pp. 5288–5291.doi:10.1109/IGARSS.2016.7730377.ISBN978-1-5090-3332-4.S2CID23975901.
Zeidler, Antonia; Jamieson, Bruce (2006). "Refinements of empirical models to forecast the shear strength of persistent weak snow layers".Cold Regions Science and Technology.44 (3). Elsevier BV:184–193.doi:10.1016/j.coldregions.2005.11.004.ISSN0165-232X.
