Snow line

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Climatic snow lines [1]
Cho Oyu - North face.jpg
Cho Oyu (8,201 m), Himalayas: 6,000 m
Cotopaxi volcano 2008-06-27T1322.jpg
Cotopaxi (5,897 m), Andes: 5,000 m
Brunegghorn and Weisshorn.jpg
Weisshorn (4,506 m), Alps: 3,000 m

The climatic snow line is the boundary between a snow-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.

Contents

Background

Snow line is an umbrella term for different interpretations of the boundary between snow-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 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 photographs, 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. [2]

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 glaciers 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. [2] The "permanent snow line" is the level above which snow will lie all year. [3]

Snow lines of global regions

The interplay of altitude and latitude affects the precise placement of the snow line at a particular location. At or near the equator, it is typically situated at approximately 4,500 metres (14,764 ft) above sea level. As one moves towards the Tropic of Cancer and Tropic of Capricorn, the parameter at first increases: in the Himalayas the permanent snow line can be as high as 5,700 metres (18,701 feet), whilst on the Tropic of Capricorn, no permanent snow exists at all in the Andes, because of the extreme aridity. Beyond the Tropics, the snow line becomes progressively lower as the latitude increases, to just below 3,000 metres (9,843 ft) in the Alps and falling all the way to sea level itself at the ice caps near the poles.[ citation needed ]

This 1848 "Sketch showing the actual elevation of the Snow Line in different Latitudes" by Alexander Keith Johnston shows the snow lines of mountains in America, Europe and Asia Scetch showing the actual elevation of the Snow Line in different Latitudes by Alexander Keith Johnston 1848.png
This 1848 "Sketch showing the actual elevation of the Snow Line in different Latitudes" by Alexander Keith Johnston shows the snow lines of mountains in America, Europe and Asia

In addition, the relative location to the nearest coastline can influence the altitude of the snow line. Areas near a coast might have a lower snow line than areas of the same altitude and latitude situated in a landmass interior due to more winter snowfall and because the average summer temperature 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 altitude is therefore necessary to lower the temperature further against the surroundings and keep the snow from melting.[ citation needed ]

Furthermore, large-scale oceanic currents such as the North Atlantic Current can have significant effects over large areas (in this case warming northern Europe, extending even to some Arctic Ocean regions).[ citation needed ]

In the Northern Hemisphere the snow line on the north-facing slopes is at a lower altitude, as the north-facing slopes receive less sunlight (solar irradiance) than south-facing slopes. [3]

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. [4]

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 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 or receding. [5] This is a very helpful tool for analyzing glaciers that are difficult to access. Using this technology we can better gauge the effects of climate change on glaciers around the world.

Records

The highest mountain in the world below the snow line is Ojos del Salado. [6]

Approximate levels

Svalbard 78°N300–600 m
Greenland 70°N100–500 m
Scandinavia at the polar circle 67°N1,000–1,500 m
Iceland 65°N700–1,100 m
Eastern Siberia 63°N2,300–2,800 m
Southern Scandinavia 62°N1,200–2,200 m
Alaska Panhandle 58°N1,000–1,500 m
Kamchatka (coastal)55°N700–1,500 m
Kamchatka (interior)55°N2,000–2,800 m
Alps (northern slopes)48°N2,500–2,800 m
Central Alps 47°N2,900–3,200 m
Alps (southern slopes)46°N2,700–2,800 m
Caucasus Mountains 43°N2,700–3,800 m
Pyrenees 43°N2,600–2,900 m
Gran Sasso d'Italia 42°N2,600–2,800 m
Pontic Mountains 41°N3,800–4,300 m
Rocky Mountains 40°N2,100–3,350 m
Karakoram 36°N5,400–5,800 m
Transhimalaya 32°N6,300–6,500 m
Himalaya 28°N6,000 m
Pico de Orizaba 19°N5,100–5,500 m
Pico Cristóbal Colón 11°N5,000–5,500 m
Rwenzori Mountains 1°N4,700–4,800 m
Mount Kenya 4,600–4,700 m
Andes in Ecuador 1°S4,800–5,000 m
New Guinea Highlands 2°S4,600–4,700 m
Kilimanjaro 3°S5,500–5,600 m
Andes in Bolivia 18°S6,000–6,500 m
Andes in Chile 30°S5,800–6,500 m
Australian Alps 36°S1,500–2,200 m
Mount Ruapehu, New Zealand 37°S2,500–2,700 m
Southern Alps, New Zealand 43°S1,600–2,700 m
Tierra del Fuego 54°S800–1,300 m
Antarctica 70°S0–400 m

[ citation needed ]

Compare the usage of "snow line" indicating the boundary between snow and non-snow. [7]

See also

Related Research Articles

Glacier Persistent body of ice that is moving under its own weight

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. Glaciers slowly deform and flow under stresses induced by their weight, creating crevasses, seracs, and other distinguishing features. They also abrade rock and debris from their substrate to create landforms such as cirques and moraines. Glaciers form only on land and are distinct from the much thinner sea ice and lake ice that forms on the surface of bodies of water.

Cryosphere Those portions of Earths surface where water is in solid form

The cryosphere is an all-encompassing term for those portions of Earth's surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps, ice sheets, and frozen ground. Thus, there is a wide overlap with the hydrosphere. The cryosphere is an integral part of the global climate system with important linkages and feedbacks generated through its influence on surface energy and moisture fluxes, clouds, precipitation, hydrology, atmospheric and oceanic circulation. Through these feedback processes, the cryosphere plays a significant role in the global climate and in climate model response to global changes. The term deglaciation describes the retreat of cryospheric features. Cryology is the study of cryospheres.

Glaciology Scientific study of ice and natural phenomena involving ice

Glaciology is the scientific study of glaciers, or more generally ice and natural phenomena that involve ice.

Aletsch Glacier

The Aletsch Glacier or Great Aletsch Glacier is the largest glacier in the Alps. It has a length of about 23 km (14 mi) (2014), has about a volume of 15.4 km3 (3.7 cu mi) (2011), and covers about 81.7 km2 (2011) in the eastern Bernese Alps in the Swiss canton of Valais. The Aletsch Glacier is composed of four smaller glaciers converging at Concordia Place, where its thickness was measured by the ETH to be still near 1 km (3,300 ft). It then continues towards the Rhône valley before giving birth to the Massa. The Aletsch Glacier is – like most glaciers in the world today – a retreating glacier. As of 2016, since 1980 it lost 1.3 kilometres (0.81 mi) of its length, since 1870 3.2 kilometres (2.0 mi), and lost also more than 300 metres (980 ft) of its thickness.

Ice shelf Large floating platform of ice caused by glacier flowing onto ocean surface

An ice shelf is a large floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are only found in Antarctica, Greenland, Northern Canada, and the Russian Arctic. The boundary between the floating ice shelf and the anchor ice that feeds it is the grounding line. The thickness of ice shelves can range from about 100 m (330 ft) to 1,000 m (3,300 ft).

Ice core Cylindrical sample drilled from an ice sheet

An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper, and an ice core contains ice formed over a range of years. Cores are drilled with hand augers or powered drills; they can reach depths of over two miles (3.2 km), and contain ice up to 800,000 years old.

Pomerape

Pomerape is a stratovolcano lying on the border of northern Chile and Bolivia. It is part of the Payachata complex of volcanoes, together with Parinacota Volcano to the south. The name "Payachata" means "twins" and refers to their appearance. It hosts glaciers down to elevations of 5,300–5,800 metres (17,400–19,000 ft), lower on the northern slope.

Glacier mass balance

Crucial to the survival of a glacier is its mass balance or surface mass balance (SMB), the difference between accumulation and ablation. Climate change may cause variations in both temperature and snowfall, causing changes in the surface mass balance. Changes in mass balance control a glacier's long-term behavior and are the most sensitive climate indicators on a glacier. From 1980–2012 the mean cumulative mass loss of glaciers reporting mass balance to the World Glacier Monitoring Service is −16 m. This includes 23 consecutive years of negative mass balances.

Glacier ice accumulation

Glacier ice accumulation occurs through accumulation of snow and other frozen precipitation, as well as through other means including rime ice, avalanching from hanging glaciers on cliffs and mountainsides above, and re-freezing of glacier meltwater as superimposed ice. Accumulation is one element in the glacier mass balance formula, with ablation counteracting. With successive years in which accumulation exceeds ablation, then a glacier will experience positive mass balance, and its terminus will advance.

Retreat of glaciers since 1850 Shortening of glaciers by melting

The retreat of glaciers since 1850 affects the availability of fresh water for irrigation and domestic use, mountain recreation, animals and plants that depend on glacier-melt, and, in the longer term, the level of the oceans. Studied by glaciologists, the temporal coincidence of glacier retreat with the measured increase of atmospheric greenhouse gases is often cited as an evidentiary underpinning of global warming. Mid-latitude mountain ranges such as the Himalayas, Rockies, Alps, Cascades, and the southern Andes, as well as isolated tropical summits such as Mount Kilimanjaro in Africa, are showing some of the largest proportionate glacial losses.

Ablation zone

Ablation zone or ablation area refers to the low-altitude area of a glacier or ice sheet below firn with a net loss in ice mass due to melting, sublimation, evaporation, ice calving, aeolian processes like blowing snow, avalanche, and any other ablation. The equilibrium line altitude (ELA) or snow line separates the ablation zone from the higher-altitude accumulation zone. The ablation zone often contains meltwater features such as supraglacial lakes, englacial streams, and subglacial lakes. Sediments dropped in the ablation zone forming small mounds or hillocks are called kames. Kame and kettle hole topography is useful in identifying an ablation zone of a glacier. The seasonally melting glacier deposits much sediment at its fringes in the ablation area. Ablation constitutes a key part of the glacier mass balance.

A periglacial lake is a lake bordering a glacier, usually found along the fringes of large ice sheets.

Subantarctic

The Subantarctic is a region in the Southern Hemisphere, located immediately north of the Antarctic region. This translates roughly to a latitude of between 46° and 60° south of the Equator. The subantarctic region includes many islands in the southern parts of the Atlantic, Indian, and Pacific oceans, especially those situated north of the Antarctic Convergence. Subantarctic glaciers are, by definition, located on islands within the subantarctic region. All glaciers located on the continent of Antarctica are by definition considered to be Antarctic glaciers.

Calderone glacier

The Calderone glacier is a glacier located in the Apennine Mountains in Abruzzo, Italy. Found in the Gran Sasso d'Italia mountain group, it lies just beneath the Corno Grande, the highest peak in the Apennines.

Tidewater glacier cycle

The tidewater glacier cycle is the typically centuries-long behavior of tidewater glaciers that consists of recurring periods of advance alternating with rapid retreat and punctuated by periods of stability. During portions of its cycle, a tidewater glacier is relatively insensitive to climate change.

Banski Suhodol Glacier Glacier in Bulgaria

The Banski Suhodol Glacier is a small glacier (glacieret) in the Pirin Mountains of Bulgaria. It lies below the Kutelo peak in the upper Banski Suhodol Valley.

Snezhnika

Snezhnika is a glacieret in the Pirin Mountains of Bulgaria, a remnant of the former Vihren Glacier. The glacieret lies at an elevation between 2,425 m (7,956 ft) and 2,480 m (8,140 ft) in the deep Golemiya Kazan cirque at the steep northern foot of Vihren, Pirin's highest summit. Due to the relatively easy access and its location along a popular hiking trail, Snezhnika is Bulgaria's most famous glacieret. Snezhnika has an average area of 0.01 km2 (0.0039 sq mi) and in 2006 it had a volume of 30,000 m3 (1,100,000 cu ft).

Ice drilling Method of drilling through ice

Ice drilling allows scientists studying glaciers and ice sheets to gain access to what is beneath the ice, to take measurements along the interior of the ice, and to retrieve samples. Instruments can be placed in the drilled holes to record temperature, pressure, speed, direction of movement, and for other scientific research, such as neutrino detection.

Glacier head Top of a glacier

A glacier head is the top of a glacier. Although glaciers seem motionless to the observer they are in constant motion and the terminus is always either advancing or retreating.

References

Footnotes

  1. Approximations. Snow line elevations retrieved from Google Earth on 2014-08-20
  2. 1 2 Vijay P. Singh, Pratap Singh, Umesh K. Haritashya (2011). Encyclopedia of Snow, Ice and Glaciers . Springer Science & Business Media. pp.  1024. ISBN   9789048126422.CS1 maint: uses authors parameter (link)
  3. 1 2 David Waugh (2000). Geography: An Integrated Approach. Nelson Thornes. p. 105. ISBN   9780174447061.
  4. Ohmura, Atsumu; Kasser, Peter; Funk, Martin (1992/ed). "Climate at the Equilibrium Line of Glaciers". Journal of Glaciology. 38 (130): 397–411. Bibcode:1992JGlac..38..397O. doi: 10.3189/S0022143000002276 . ISSN   0022-1430.Check date values in: |date= (help)
  5. Leonard, Katherine C.; Fountain, Andrew G. (2003/ed). "Map-based methods for estimating glacier equilibrium-line altitudes". Journal of Glaciology. 49 (166): 329–336. Bibcode:2003JGlac..49..329L. doi: 10.3189/172756503781830665 . ISSN   0022-1430.Check date values in: |date= (help)
  6. Regional Climate and Snow/Glacier Distribution in Southern Upper Atacama (Ojos del Salado) – an integrated statistical, GIS and RS based approach
  7. Adam, Steve; Alain Pietroniro; Melinda M. Brugman (1997). "Glacier Snow Line Mapping Using ERS-1 SAR Imagery". Remote Sensing of Environment. New York: Elsevier Science Inc. 61 (1): 46–54. Bibcode:1997RSEnv..61...46A. doi:10.1016/S0034-4257(96)00239-8. The snow line at the end of the ablation season is roughly equal to the equilibrium line altitude (ELA) for temperate glaciers