The climatic snow line is the boundary between a

snow Snow comprises individual ice crystals that grow while suspended in the atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet ...

-covered and snow-free surface. The actual snow line may adjust seasonally, and be either significantly higher in elevation, or lower. The permanent snow line is the level above which snow will lie all year.

Background

Snow line is an umbrella term for different interpretations of the boundary between

-covered surface and snow-free surface. The definitions of the snow line may have different temporal and spatial focus. In many regions the changing snow line reflect seasonal dynamics. The final height of the snow line in a

mountain A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually higher t ...

environment at the end of the melting season is subject to climatic variability, and therefore may be different from year to year. The snow line is measured using automatic cameras,

aerial photograph Aerial photography (or airborne imagery) is the taking of photographs from an aircraft or other airborne platforms. When taking motion pictures, it is also known as aerial videography. Platforms for aerial photography include fixed-wing airc ...

s, or satellite images. Because the snow line can be established without on-the-ground measurements, it can be measured in remote and difficult to access areas. Therefore, the snow line has become an important variable in hydrological models. The average elevation of a transient snow line is called the "climatic snow line" and is used as a parameter to classify regions according to climatic conditions. The boundary between the accumulation zone and the ablation zone on

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such a ...

s is called the "annual snow line". The glacier region below this snow line was subject to melting in the previous season. The term "orographic snow line" is used to describe the snow boundary on surfaces other than glaciers. The term "regional snow line" is used to describe large areas. The "permanent snow line" is the level above which snow will lie all year.

Snow lines of global regions

The interplay of

elevation The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § ...

and

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north po ...

affects the precise placement of the snow line at a particular location. At or near the

equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can al ...

, it is typically situated at approximately above

sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardise ...

. As one moves towards the

Tropic of Cancer The Tropic of Cancer, which is also referred to as the Northern Tropic, is the most northerly circle of latitude on Earth at which the Sun can be directly overhead. This occurs on the June solstice, when the Northern Hemisphere is tilted tow ...

and Tropic of Capricorn, the parameter at first increases: in the

Himalayas The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over ...

the permanent snow line can be as high as , whilst on the Tropic of Capricorn, no permanent snow exists at all in the

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

, because of the extreme aridity. Beyond the Tropics, the snow line becomes progressively lower as the latitude increases, to just below in the

Alps The Alps () ; german: Alpen ; it, Alpi ; rm, Alps ; sl, Alpe . are the highest and most extensive mountain range system that lies entirely in Europe, stretching approximately across seven Alpine countries (from west to east): France, ...

and falling all the way to sea level itself at the ice caps near the poles. Scetch showing the actual elevation of the Snow Line in different Latitudes by Alexander Keith Johnston 1848

Scetch showing the actual elevation of the Snow Line in different Latitudes by Alexander Keith Johnston 1848

In addition, the relative location to the nearest coastline can influence the elevation of the snow line. Areas near a coast might have a lower snow line than areas of the same elevation and latitude situated in a landmass interior due to more winter snowfall and because the average summer

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied on ...

of the surrounding lowlands would be warmer away from the sea. (This applies even in the tropics, since areas far from the sea will have larger diurnal temperature ranges and potentially less moisture, as observed with Kilimanjaro and presently glacier-free Mount Meru.) A higher elevation is therefore necessary to lower the temperature further against the surroundings and keep the snow from melting. Furthermore, large-scale oceanic currents such as the

North Atlantic Current The North Atlantic Current (NAC), also known as North Atlantic Drift and North Atlantic Sea Movement, is a powerful warm western boundary current within the Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five ocean ...

can have significant effects over large areas (in this case warming northern Europe, extending even to some Arctic Ocean regions). In the Northern Hemisphere the snow line on the north-facing slopes is at a lower elevation, as the north-facing slopes receive less sunlight (

solar irradiance Solar irradiance is the power per unit area ( surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metr ...

) than south-facing slopes. The converse will occur in the Southern Hemisphere.

Glacier equilibrium line

The glacier equilibrium line is the point of transition between the accumulation zone and ablation zone. It is the line where the mass of these two zones is equal. Depending on the thickness of the glacier, this line can seem as though it is leaning more towards one zone but it is determined by the actual mass of ice in either zone. The rates of ablation and accumulation can also be used to determine the location of this line. This point is an important location to use in determining whether a glacier is growing or shrinking. A higher glacier equilibrium line will indicate that the glacier is shrinking, whereas a lower line will indicate that the glacier is growing. The terminus of a glacier advances or retreats based on the location of this equilibrium line. Scientists are using

remote sensing Remote sensing is the acquisition of information about an object or phenomenon without making physical contact with the object, in contrast to in situ or on-site observation. The term is applied especially to acquiring information about Ear ...

to better estimate the locations of this line on glaciers around the world. Using satellite imagery, scientists are able to identify whether the glacier is

growing Growing may refer to: * Growth (disambiguation) * Growing (band), a noise band based in Brooklyn, New York * ''Growing'' (Sleeping People album), 2007 *Growing (Rina Chinen album) * Growing, a children's song sung on the television program Barney ...

or receding. This is a very helpful tool for analyzing glaciers that are difficult to access. Using this

technology Technology is the application of knowledge to reach practical goals in a specifiable and reproducible way. The word ''technology'' may also mean the product of such an endeavor. The use of technology is widely prevalent in medicine, scie ...

we can better gauge the

effects of climate change The effects of climate change impact the physical environment, ecosystems and human societies. The environmental effects of climate change are broad and far-reaching. They affect the water cycle, oceans, sea and land ice ( glaciers), sea l ...

on glaciers around the world.

Records

The highest mountain in the world below the snow line is Ojos del Salado.

Approximate levels

Compare the usage of "snow line" indicating the boundary between snow and non-snow.

References

*Charlesworth J.K. (1957). The quaternary era. With special reference to its glaciation, vol. I. London, Edward Arnold (publishers) Ltd, 700 pp. *Flint, R. F. (1957). Glacial and Pleistocene geology. John Wiley & Sons, Inc., New York, xiii+553+555 pp. *Kalesnik, S.V. (1939). Obshchaya glyatsiologiya eneral glaciology Uchpedgiz, Leningrad, 328 pp. (in Russian) *Tronov, M.V. (1956). Voprosy svyazi mezhdu klimatom i oledeneniem he problems of the connection between climate and glaciation Izdatel'stvo Tomskogo Universiteta, Tomsk, 202 pp. (in Russian) *Wilhelm, F. (1975). Schnee- und Gletscherkunde now- and glaciers study De Gruyter, Berlin, 414 pp. (in German) *Braithewaite, R.J. and Raper, S.C.B (2009). "Estimating Equilibrium Line Altitude (ELA) From Glacier Inventory Data." ''Annals of Glaciology'', 50, pp. 127–132. . *Leonard, K.C., and Fountain, A.G. (2003). "Map-Based Methods for Estimating Glacier Equilibrium-Line Altitudes." ''Journal of Glaciology'', vol. 49, no. 166, pp. 329–336., . *Ohmura, A., Kasser, P., and Funk, M. (1992). "Climate at the Equilibrium Line of Glaciers." ''Journal of Glaciology'', vol. 38, no. 130, pp. 397–411., . *Carrivick, J.L., Lee, J. and Brewer, T.R. (2004). "Improving Local Estimations and Regional Trends of Glacier Equilibrium Line Altitudes." ''Geografiska Annaler: Series A, Physical Geography'', vol. 86, no. 1, pp. 67–79. . *Benn, D.I., and Lehmkuhl, F. (2000). "Mass balance and equilibrium-line altitudes of glaciers in high-mountain environments." ''Quaternary International'', 65/66, pp. 15–29.

Footnotes

{{reflist Snow Snow or ice weather phenomena Climate zones Montane ecology