Ice sheets, ice caps and valley glaciers compose the main elements of glacial environments. Many different processes deriving from their movement, as well as marine aeolian and fluvial influences, affect these environments putting them amongst the most complex present on Earth today.
Vital to the health of a glacier is its mass balance. Mass balance comprises of accumulation; all processes that add mass to a glacier, minus ablation; all processes that subtract mass from a glacier in a given year.
Determining the health of a glacial system is dependent on mass balance. A glacier with a positive mass balance is out of equilibrium with processes of accumulation being larger than that of ablation, causing the glacier to advance. If it has a negative mass balance it is also out of equilibrium but will cause the glacier to retreat.
The upper region of a glacier is known as the accumulation zone and experiences mass gain predominantly during autumn and winter months when snowfall, avalanching and the freezing of rain are most likely to occur and result in a net gain of ice. In this zone there is survival of firn, snow that is wetted and compacted becoming re-crystalised into a more dense substance and finally becoming ice. Towards the snout of a glacier is the ablation zone and although it may experience snowfall during the winter months, it does not avoid net mass loss during the year. Processes of surface melt and the subsequent run-off, internal melt, geothermal heat transfer, evaporation and wind erosion, all result in loss of ice from the glacier and usually occur during the summer months. During the autumn and spring months accumulation and ablation are generally balanced and ice mass remains fairly constant. The division between the accumulation and ablation zones is known as the equilibrium line.
... -out and the tare. Electonic balance can measure mass to the precision of 0.0001. Electonic balance has the tare feature which resets ... and the other liquid component is left behind. In this process, vaporization and condensation occur side by side (Thinkwell, 2012). A ... you can show the more the efficacy of the separation process (Thinkwell, 2012). (e) (1 pts) What is meant by “bumping ...
In order to retain equilibrium and compensate for accumulation and ablation, glaciers must move. These changes are propagated down the glacier by kinematic waves; ice flows moving down-slope by internal deformation and sometimes causing a protuberance in the ice surface as it spreads out the ice. Kinematic waves have a faster velocity than the ice and may initiate advancement at the snout when reached, which can take years. The rate at which this occurs is restricted principally by the slope, basal thermal and physical conditions. The distance a glacier will advance is determined solely by the amount of available ice, however, not by the kinematic wave itself (Paterson 1981) .
Variation in ice-thickness in the upper and middle sections of a glacier may be diminutive as it is the snout which is particularly susceptible to changes in mass balance.
Response times to mass balance changes also vary significantly from place to place and are dependent on the length and thickness of the glacier and the ablation at the snout. In general, small, high gradient, high-velocity, thin, temperate glaciers have a quick response time, reacting within a few years. For example, cirque glaciers may take as little as one to two years to respond, valley glaciers from 5 to 100 years. On the other hand, large, low-gradient, low velocity, thick, cold glaciers, global warming Ice Sheets Melting">ice sheet may take thousands of years to respond, such as the Antarctic ice sheet which takes up to 5,000 years.
Many different techniques are used to measure mass balance. Methods within the accumulation zone include snow pits, a fairly simple method involving digging through the previous winters residual snow pack to determine its depth. Probing is used in conjunction with temperate glaciers and comprises of inserting a probe into the ice until resistance increases suddenly indicating that the tip has reached the ice formed the previous year. Crevasse stratigraphy is used to measure accumulation in vertically walled crevasses making use of the distinguishable annual layer dirt bands which reflect summer dirt deposition and other seasonal effects. This method has its advantages as it can be used in cold regions where probing is not feasible.
... any current which is about radically changing the model. It's just me, really." Hancock ... about refining the model. It's not about changing the model radically. I'm not aware of ... dry until 12, 000 years ago. It was a wonderful refuge from the Ice Age world." Hancock complains ... how different the world was during the Ice Age - enormous ice caps across northern Europe, extremely dry and ...
To measure mass balance in an ablation zone, stakes are driven into the glacier at the beginning of the melt season. Surface melt on the glacier runs-off to reveal a certain amount of the stake, which is then measured. Numerous stakes placed in the ablation zone enable measurement of net ablation. The mass balance for an individual body of ice is usually expressed as the rate of change of the equivalent volume of liquid water, in m3/yr; the mass balance is zero for a steady state .
There is some controversy surrounding the relationship between mass balance and climate. Recent media attention has focused upon global warming, suggesting that as we increase the burning of fossil fuels we add carbon dioxide into the atmosphere and increase the temperature of the Earths atmosphere through the greenhouse effect. Subsequently, it is proposed that these processes will result in the melting of glaciers and ice sheets leading to a rise in sea levels.
However, as previously stated, it can take thousands of years for huge ice sheets such as the Antarctic to respond to changes in mass balance, making it difficult to determine how large ice masses respond to global warming induced by human activity.
According to Drewry (1991) , there are three main consequences of global warming for ice sheets like the Antarctic: ice temperature rise and attendant ice flow changes; enhanced basal melting beneath ice shelves and changes in mass balance. As the warming of ice increases discharge into the oceans, it has been blamed for the recent sea level. However, such ice sheets can be up to 4000m thick and are therefore only susceptible to slow vertical conduction of heat, a long process taking up to 1,000 years. Also, due to the particularly cold interior of the Antarctic ice sheet, the surrounding atmospheric moisture content is low, restraining the accumulation that occurs. Therefore, an increase in global temperature may lead to higher amounts of precipitation and snow accumulation rather than the proposed ablation.
... Antarctic Ice Sheets and the East Antarctic Ice Sheets. Together the East and the West ice sheets hold about 91 percent of the worlds glacial ice. The west Antarctic ice sheet ... the possible effects of global warming on the ice sheets, but until there is proof that the ice sheets are melting, it is ... and over the years has become an enormous mass of ice. By learning about the past transformations of the ...
Other studies too dismiss changes in mass balance of glaciers as an indication of global warming. Bennett (2003) studied ice streams and found evidence to support the theory that although ice streams have high velocities and varying mass balances, collectively on a local scale, they seem to be in balance with one and other. On occasions, even positive mass balances were identified.
Conversely, there is a huge amount of evidence to suggest the contrary. Gregory et al (2004) argue that the Greenland ice sheet, as it has a lower mass balance than the Antarctic, could be eliminated by a 30C increase in global temperatures, subsequently causing a sea-level rise of 7m over a 1,000 year period.
Studies of the West Antarctic Ice Sheet (WAIS) have been the catalyst for many fears over melting ice sheets and rises in sea level. Unlike the East Antarctic Ice Sheet, the WAIS is more unstable as it is a marine ice sheet resting on a bed well below sea level. An intermediate view by Robin (1986) contends that ‘catastrophic collapse of the West Antarctic ice sheet is not imminent… [but] a global rise of 3.50C might start a collapse by the end of next century’. He goes on to suggest that even if this did happen, it would take at least 200 years to raise sea level by another 5m.
Compounding evidence has been found by recent satellite observations. This evidence suggests pronounced regional warming has triggered the collapse of ice shelves within the Antarctic Peninsula leading to a ten-fold increase in ice sheet retreat. Highlighted in this study by Rignot E (2006) is the ice shelves vulnerability to changes in the climate and their significant negative effect on the Antarctic ice sheets mass balance. The Pine Island Glacier mass loss accelerated 38% since 1975, and most of the speed up took place over the last decade.
... and become known as Ice Sheets. As long more snow falls than ice melts, Ice Sheets will continue to expand. Ice Sheets NEVER move backwards- although ... the continental glacier, some rough topography was formed. These ice sheets, however, due to their erosion capabilities, can also work ... rivers, and even oceans. One example of ice sheets melting isBritain's sheets that melted from the lowlands in just a ...
Both sides put forward convincing arguments and evidence for and against the major impact of the climate on mass balance of glaciers. There is a great deal of scientific evidence to suggest that it takes thousands of years for huge ice sheets such as the Antarctic to respond to changes in climate, which would further suggest that today’s global warming would not have a great impact on today’s climate. However, smaller ice sheets as Greenland are likely to be affected in the shorter term and therefore an impact on today’s population.