Snow line

This article is about the geographical feature. For the boundary in a protoplanetary disk, seeFrost line (astrophysics).

Climatic snow lines

Cho Oyu(8,201 m), Himalayas: 6,000 m

Cotopaxi(5,897 m), Andes: 5,000 m

Weisshorn(4,506 m), Alps: 3,000 m

The climaticsnow lineis the boundary between asnow-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 betweensnow-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 reflectseasonaldynamics. The final height of the snow line in amountainenvironment 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 photographs,orsatellite 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 inhydrological 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 onglaciersis 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 ofelevationandlatitudeaffects the precise placement of the snow line at a particular location. At or near theequator,it is typically situated at approximately 4,500 metres (15,000 ft) abovesea level.As one moves towards theTropic of CancerandTropic of Capricorn,the parameter at first increases: in theHimalayasthe permanent snow line can be as high as 5,700 metres (19,000 feet). Beyond theTropics,the snow line becomes progressively lower as the latitude increases, to just below 3,000 metres (9,800 ft) in theAlpsand falling all the way to sea level itself at theice capsnear thepoles.

This 1848 "Sketch showing the actual elevation of the Snow Line in different Latitudes" byAlexander Keith Johnstonshows the snow lines of mountains in America, Europe and Asia

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 alandmassinterior due to more winter snowfall and because the average summertemperatureof 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 withKilimanjaroand presently glacier-freeMount 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 theNorth Atlantic Currentcan have significant effects over large areas (in this case warming northern Europe, extending even to some Arctic Ocean regions).

In theNorthern Hemispherethe snow line on the north-facing slopes is at a lower elevation, as the north-facing slopes receive less sunlight (solar irradiance) than south-facing slopes.The converse will occur in the SouthernHemisphere.

Glacier equilibrium line

The glacierequilibriumline is the point of transition between theaccumulation zoneandablation 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 actualmass of icein either zone. The rates ofablationandaccumulationcan 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. Theterminusof a glacier advances or retreats based on the location of this equilibrium line.

Scientists are usingremote sensingto better estimate the locations of this line on glaciers around the world. Usingsatellite imagery,scientists are able to identify whether the glacier is growing or receding.This is a very helpful tool for analyzing glaciers that are difficult to access. Using thistechnologywe can better gauge theeffects of climate changeon glaciers around the world.

Records

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

See also

• Frost line
• Frost line (astrophysics)
• Glacier
• High Alps
• Ice cap climate
• Tree line

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 [General glaciology]. Uchpedgiz, Leningrad, 328 pp. (in Russian)
• Tronov, M.V. (1956). Voprosy svyazi mezhdu klimatom i oledeneniem [The problems of the connection between climate and glaciation]. Izdatel'stvo Tomskogo Universiteta, Tomsk, 202 pp. (in Russian)
• Wilhelm, F. (1975). Schnee- und Gletscherkunde [Snow- 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.doi:10.3189/172756410790595930.
• 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.,doi:10.3189/172756503781830665.
• 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.,doi:10.3189/S0022143000002276.
• 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.JSTOR3566202.
• 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.doi:10.1016/S1040-6182(99)00034-8