2481145 Rock Glaciers Jas
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[Writer's surname]
1
[Writer’s name] [Professor’s name] [Course title] [Date] Rock Glaciers Introduction Rock glaciers are amongst the most breath-taking and most widespread periglacial occurrences on earth. Perhaps, the most comprehensive definition is A suitable descriptive definition of a rock glacier is presented by Potter (1972) and Washburn (1979). According to them a rock glacier is “a tongue-like or lobate body, usually of angular boulders, that resembles a small glacier, generally occurs in high mountainous terrain and usually has ridges, furrows, and sometimes lobes on its surface, and has a steep front at the angle of repose.” Another notable definition is provided by Potter Jr., N. in 1972. He says "...a tonguelike or lobate body, usually of angular boulders, that resembles a small glacier, generally occurs in high mountainous terrain and usually has ridges, furrows, and sometimes lobes on its surface, and has a steep front at the angle of repose.” Whereas Encyclopedia Britannica has provided the following definition “Tongue like body of coarse rock fragments, found in high mountains above the timberline that moves slowly down a valley. The rock material usually has fallen from the valley walls and may contain large boulders: it resembles the material left at the terminus of a true glacier. Interstitial ice usually occurs in the centre of rock glaciers. Where the ice approaches the
[Writer's surname]
2
terminus, it melts and releases the rock material, which then forms a steep talus slope. A rock glacier may be 30 meters (100 feet) deep and nearly 1 1/2 kilometers (about 1 mile) long.” They may be classified as active or inactive glaciers depending on their motion or the lack of it. Active rock glaciers continuously move down-slope or down-valley as a result of internal deformation of ice, supposedly as a manifestation of basal gliding. The top part of an active rock glacier moves faster than its basal part. As a result of it near the toe end of a rock glacier material rolled down form the top of the glacier starts forming a slope. It is by looking at this signature slope at the toe, any geologist can easily recognize the rock glacier and whether it is active or not. Their estimated velocities range from centimeters/year to quite a few meters/year. In the Alaskan range upper surfaces of active rock glaciers have been recorded to move forward at a rate of a meter per year, while the flow of the front is nearly half that figure. The disappearance of foundation of rock debris or as a repercussion of increased warmth in climate, an active rock glacier may ultimately change into an inactive one. A rock glacier requires several necessary conditions to exist. Firstly, there should be a source of blocky rock. Secondly, the average annual temperature should be low enough for water to freeze and to form the characteristic ice matrix in the spaces between the rocks. Lastly, a slope for the rock glacier to move along as it is gravity that gives life to such glacier. Their origin is still a reason of controversy amongst researchers. Some of them hypothesize that they are solely the consequence of periglacial processes whereas others argue that they may also have evolved from debris-covered glaciers. Rock glaciers with permafrost origins are also termed as "ice-cemented rock glaciers", and those with glacial origins as "ice-cored rock glaciers".
[Writer's surname]
3
Usually they are found at heights more than 2000m above sea surface. There are a number of regions in the world where the abundance of the phenomenon has provided researchers ample opportunities for study and research. Central Alps especially near Austria and Andes near Peru and Chile are two of the most famous regions. The phenomenon can also be observed in the Himalayan range and Afghanistan. In US they can be found by dozens in the Alaskan Range. They also occur in the San Juan range in Colorado, in Wyoming and the Sierra Nevada in California. Their largest concentration is found on Disko Island (West Greenland) (at least 200). They are also in abundance in Iceland, Kazakhstan and Svalbard. . Besides Active and Inactive glaciers the other famous type is Fossil rock glaciers, which does not contain any ice, usually all the ice has melted out, its surface, especially the frontal slope, is often found to be covered by vegetation, the inclination of the frontal slope is normally less steeper than that of their Active counterparts. They may naturally occur in many shapes. They may be tongue-shaped, lobate or of complex shapes. Tongue-Shaped
Lobate
Complex
[Writer's surname]
4
Dimensions Mostly rock glaciers have length of a few hundred, a width of 50 - 200 meters and an area of nearly 0.2 km². Reichenkar rock glacier (western Stubai Alps), which has a length of 1400 m, is considered as one of the longest rock glaciers. Structure The surface is covered by a coarse grained debris layer (which is the active layer), underlain by a core of frozen debris and/or sometimes ice. The surface of most of the active rock glaciers is differentiated by some well developed networks of ridges and furrows both longitudinally and transversally. The frontal slope of an active rock glacier is typified by an almost vertical gradient (in the range of 40 - 45°) and is devoid of any vegetation. It is usually composed of fresh and unweathered matter.
[Writer's surname]
5
In the base of some rock glaciers a depression similar to the shape of a spoon gets developed as a result of the melting of huge mass of ice under the upper layer of debris. Temperatures recorded in the debris layer The temperature in the debris layer shows complex behavior. It depends on various factors, especially the weather, the distribution on the basis of grain-size, the thickness of the layer of debris and the core ice inside. As expected, a rapid decrease in temperature can be observed from the surface region to a depth as less as 150 cm. Generally, the minimum temperature can be recorded between 10-12 in the evening and maximum temperature between 6-12 in the morning. Temperatures recorded at the base of the winter snow cover (Below the Surface) As a thick snow layer acts as an insulating layer, temperature at the base of a winter snow cover gets mainly influenced by only the heat flow from underlying ground ice. That is why temperatures at the basal part do not show temperature variations on daily basis. The recorded temperature in active rock glaciers is usually found to be below -3°C (a normal indication of permafrost), while on ground free from this phenomenon it is notably higher i.e. in the range of -0.3°C and -1°C. Hydrology Temperature of the melted water gushing out in the form of springs from active rock glaciers is generally very low and is recorded in the range of 0.4-0.9°C. This shows that this spring water was in direct contact with ice while passing through the rock glacier. This discharge of water from active rock glaciers is affected strongly by seasonal and diurnal variations. It is controlled by several factors such as the thickness of the winter snow layer, the whole size of rock glacier and the drainage area, the existence of one or many cirque glaciers in drainage area, the layer thickness and the grain size of the debris of the
[Writer's surname]
6
active layer, the groundwater abundance or scarcity and the general weather during the melt period, especially summer thunderstorms, resulting in a noticeable seasonal and diurnal variations. The water released from these springs may be a result of many independent phenomena. Like it may have come from snowmelt or melting of permafrost or glacier ice or atmospheric precipitation in summer may also be a reason of it.
Fig. Debris-ice components in mountainous area with suggested terminology for the main features and alternative terms in parentheses. After Martin and Whalley (1987), Humlum (1988), and Hamilton and Whalley (1995). (Source: Whalley, W. B., and F. Azizi, 2003) Electrical conductivity of the water, during cold weather periods, is generally low as the water is mostly derived from snow/ice and/or precipitation, it gets high in autumns when melting is low and the discharge is normally consist of groundwater. An interesting discovery in the modern age was the proof of presence of similar to earth rock glaciers on the surface of Mars. A lot of research is still needed before someone
[Writer's surname]
7
can put something conclusive about this discovery as they can, until now, best be described as “rock glacier-like features”. (Malin, M. C., et al., 2001) Rock Glacier Formation Geologists, over the years, have proposed several hypotheses about rock glacier formation. Despite all the difference of opinions all the hypotheses agree on one thing i.e. a necessity of prolonged cold conditions (same conditions as that of permafrost). Supposing if a glacier is large enough, it can maintain its own internal microclimate. There have been three main models of rock glacier formation which are proposed and discussed in detail by Whalley and Martin (1992), namely a permafrost origin, a glacierderived origin, and a mass-wasting (landslide) origin. The first two are based on the creep of ice while the third (the most likely one) may involve, but does not need, the presence of ice. These models are briefly discussed below: Permafrost Model The permafrost model for rock glacier formation is based on the ideas of Wahrhaftig and Cox (1959) and has been propagated in particular by Barsch (1996) and Haeberli (1985). The “congelation” ice formed from freezing water (either by ice segregation or water injection under pressure). An important requirement is an average annual air temperature of, at most, -1.5°C. This thermal condition implies a “zonal” occurrence of rock glaciers and this attribute has led to the use of rock glaciers as being indicators of permafrost, both present and relict (Barsch, 1996). The presence of any glacier ice which plays a part in the formation of rock glaciers is generally disputed by adherents to this model. The literature often implies that rock glaciers necessarily have a permafrost origin. Glacial Model
[Writer's surname]
8
The glacial model (for a comprehensive review, see Whalley and Martin, 1992), relies on the preservation of a thin (generally <50 m) body of ice by an insulating weathered rock debris layer. The ice is considered to be derived from glacial, i.e., “sedimentary” sources. The thin ice creeps, giving a typically low velocity and the debris preserves this in an otherwise ablation-dominant environment. The controls on maintaining this buried ice are thus related to thickness of debris cover as much as local climate (measured by, e.g., degree-day estimates). As such, they are “azonal” features and cannot be used to delimit temperature regimes such as the presence of permafrost. Landslide Model The landslide, or “catastrophic,” model (Johnson, 1974, 1984) has used similarity of topographic form to suggest that rock glaciers may be derived from rapid landslides/rock avalanches (Bergsturtz or Sturtzstroms) (Whalley, 1976; Whalley and Martin, 1992). These will generally be forms which do not flow after emplacement. However, it has been recognized that some Bergsturz have fallen on retreating/down-wasting glaciers and so have produced “instant” rock glaciers. This is a variation of the glacier ice cored model rather than the landslide model (Whalley, 1976). In the case of fossil rock glaciers, it may not be easy or possible to distinguish between these origins. When a pile of debris at the basal part of a cliff (also known as talus) gets saturated with freezing and liquefying water, it may tend to slowly move just like a glacier (normally the mass-wasting movement is slower and less noticeable as it usually has a very low angle of repose). Whereas in true glacier movements as a result of the pressure from the weight of the ice pack itself compressing the underneath lying ice until it becomes plastic and starts flowing slowly, in this particular kind of rock glacier it is mainly the melting of the ice that results in that flow. It can be also be compared with solifluction, however the rocks involved here provide the flow a much steeper angle of repose, depicting the appearance of a true
[Writer's surname]
9
glacial flow. Usually in these types of cases flow may sometimes be aided by the glacier standing directly on top of permafrost (which does not absorb the melting water). Conclusion Interpretation of many Martian surface forms has, currently, to be done by comparison with terrestrial landforms. For “rock glaciers” this seems to be particularly troublesome. Unfortunately, not only is there a lack of agreement on the terrestrial forms and their significance but there is also little about the nature or volume of any ice bodies found. For example, a glacial model for a rock glacier implies that it is likely to contain much more ice than if a permafrost model was applicable. Conversely, creep of a deforming body containing little ice may take place over many thousands of years. That ice is a major, probably the only, reason for flow in these debris masses seems to be clear but the identification of the volumes and their location is difficult on Earth and Mars. Modeling of ice bodies under Martian temperatures (Colaprete and Jakosky, 1998) and FE modeling, of rock glaciers and protalus lobes with variations of the component mixtures (Azizi and Whalley, 1995) shows a way forward. It is probably necessary to combine the flow model with suppositions of where the ice may be located. Not only would this apply to various forms of ice-rock debris composite but might also be used to test the origin of the water source. However, there are still difficulties in knowing which constitutive equations to use (ice-rock mixture ratios as much as temperature) let alone the actual thickness of the body and ice location. Effective shear stresses acting on deforming ice requires knowledge of both the thickness of material, deforming and rigid, at any location. There is still a paucity of information in terrestrial rock glacier systems which relates topographic features to rheology.
[Writer's surname] 10 Ground Penetrating Radar (GPR) is possibly the end of arguments about the internal structure of these rock glaciers (Degenhardt, John J. Jr. et al. 2002). With the advancement in science as a whole and particularly in the field of geology we can foresee a time when, like so many other phenomenon of nature, the mystery of the formation of rock glaciers will also be solved.
Works Cited Brenning, A. Statistical Estimation and Logistic Regression Modeling of Rock Glacier Distribution in the Andes of Santiago, Central Chile. Geographisches Institut, Humboldt–Universität zu Berlin. Burger, K. C.; Degenhardt, J. J.; Giardino, J. R. Engineering geomorphology of rock glaciers. Geomorphology. Volume 31, Number 1, p. 93-132. Elsevier. December 1999. Davis, T. Neil. Rock Glaciers. Article #251. Alaska Science Forum. September 7, 1978. Degenhardt, John J. Jr. et al. The Internal Structure of Rock Glaciers and Geomorphologic Interpretations: Yankee Boy Basin, CO, USA and Hiorthfjellet and Prins Karls Forland, Svalbard. The Geological Society of America (GSA). Paper No. 115-4. 2002 Denver Annual Meeting. October 27-30, 2002. Giardino, J. R., J. F. Shroder, et al. Rock Glaciers. London, Allen & Unwin. 1987.
[Writer's surname] 11 Goolsby, Jimmy Earl. East rock glacier of Lone Mountain, Madison County, Montana. Montana State University. Bozeman, Montana. June 1972. Ikeda, A. Combination of Geophysical Methods for Measuring the Structure of Rock Glaciers. American Geophysical Union. Fall Meeting 2007. Johnson, P. G. "Rock glacier types and their drainage systems, Grizzly Creek, Yukon Territory." Canadian Journal of Earth Sciences. Issue 15, p. 1496-1507. 1978. Johnson, Peter G. Mass Movement of Ablation Complexes and Their Relationship to Rock Glaciers. Geografiska Annaler. Series A, Physical Geography, Vol. 56, No. 1/2, pp. 93-101. Blackwell Publishing on behalf of the Swedish Society for Anthropology and Geography. 1974. Konrad, S. K., N. F. Humphrey, et al. "Rock glacier dynamics and paleoclimatic implications." Geology. Volume 27, Number 9, p. 1131-1134. 1999. Leysinger Vieli, G. J. M. C.; Gudmundsson, G. H. Evolution of rock glaciers and alpine glaciers: A model-model approach. Proceedings of the 8th International Conference on Permafrost, Zurich, Switzerland. 2003. Malin, M. C., et al., SW Candor layered floor terrain, in NASA Planetary Photojournal, image M2101824, NASA, Washington, D. C. 2001. Potter Jr., N. Ice-cored rock glacier, Galena Creek, northern Absaroka Mountains, Wyoming. Geological Society of America Bulletin, Issue 83, p. 3025-3057. 1972. Steig, Eric J.; Clark, Douglas H.; Potter Jr., Noel; Gillespie, Alan R.. The geomorphic and climatic significance of rock glaciers. Geografiska Annaler: Series A, Physical Geography. Volume 80, Number 3-4, p. 173-174. 1998.
[Writer's surname] 12 Whalley, W. B., and F. Azizi, Rock glaciers and protalus landforms: Analogous forms and ice sources on Earth and Mars, Journal of Geophysical Research. 108(E4), 8032, doi:10.1029/2002JE001864, 2003. Whalley, W. B.; H. E. Martin. "Rock glaciers:II models and mechanisms." Progress in Physical Geography. Volume 16, Number 2, p. 127-186. 1992.
1
[Writer’s name] [Professor’s name] [Course title] [Date] Rock Glaciers Introduction Rock glaciers are amongst the most breath-taking and most widespread periglacial occurrences on earth. Perhaps, the most comprehensive definition is A suitable descriptive definition of a rock glacier is presented by Potter (1972) and Washburn (1979). According to them a rock glacier is “a tongue-like or lobate body, usually of angular boulders, that resembles a small glacier, generally occurs in high mountainous terrain and usually has ridges, furrows, and sometimes lobes on its surface, and has a steep front at the angle of repose.” Another notable definition is provided by Potter Jr., N. in 1972. He says "...a tonguelike or lobate body, usually of angular boulders, that resembles a small glacier, generally occurs in high mountainous terrain and usually has ridges, furrows, and sometimes lobes on its surface, and has a steep front at the angle of repose.” Whereas Encyclopedia Britannica has provided the following definition “Tongue like body of coarse rock fragments, found in high mountains above the timberline that moves slowly down a valley. The rock material usually has fallen from the valley walls and may contain large boulders: it resembles the material left at the terminus of a true glacier. Interstitial ice usually occurs in the centre of rock glaciers. Where the ice approaches the
[Writer's surname]
2
terminus, it melts and releases the rock material, which then forms a steep talus slope. A rock glacier may be 30 meters (100 feet) deep and nearly 1 1/2 kilometers (about 1 mile) long.” They may be classified as active or inactive glaciers depending on their motion or the lack of it. Active rock glaciers continuously move down-slope or down-valley as a result of internal deformation of ice, supposedly as a manifestation of basal gliding. The top part of an active rock glacier moves faster than its basal part. As a result of it near the toe end of a rock glacier material rolled down form the top of the glacier starts forming a slope. It is by looking at this signature slope at the toe, any geologist can easily recognize the rock glacier and whether it is active or not. Their estimated velocities range from centimeters/year to quite a few meters/year. In the Alaskan range upper surfaces of active rock glaciers have been recorded to move forward at a rate of a meter per year, while the flow of the front is nearly half that figure. The disappearance of foundation of rock debris or as a repercussion of increased warmth in climate, an active rock glacier may ultimately change into an inactive one. A rock glacier requires several necessary conditions to exist. Firstly, there should be a source of blocky rock. Secondly, the average annual temperature should be low enough for water to freeze and to form the characteristic ice matrix in the spaces between the rocks. Lastly, a slope for the rock glacier to move along as it is gravity that gives life to such glacier. Their origin is still a reason of controversy amongst researchers. Some of them hypothesize that they are solely the consequence of periglacial processes whereas others argue that they may also have evolved from debris-covered glaciers. Rock glaciers with permafrost origins are also termed as "ice-cemented rock glaciers", and those with glacial origins as "ice-cored rock glaciers".
[Writer's surname]
3
Usually they are found at heights more than 2000m above sea surface. There are a number of regions in the world where the abundance of the phenomenon has provided researchers ample opportunities for study and research. Central Alps especially near Austria and Andes near Peru and Chile are two of the most famous regions. The phenomenon can also be observed in the Himalayan range and Afghanistan. In US they can be found by dozens in the Alaskan Range. They also occur in the San Juan range in Colorado, in Wyoming and the Sierra Nevada in California. Their largest concentration is found on Disko Island (West Greenland) (at least 200). They are also in abundance in Iceland, Kazakhstan and Svalbard. . Besides Active and Inactive glaciers the other famous type is Fossil rock glaciers, which does not contain any ice, usually all the ice has melted out, its surface, especially the frontal slope, is often found to be covered by vegetation, the inclination of the frontal slope is normally less steeper than that of their Active counterparts. They may naturally occur in many shapes. They may be tongue-shaped, lobate or of complex shapes. Tongue-Shaped
Lobate
Complex
[Writer's surname]
4
Dimensions Mostly rock glaciers have length of a few hundred, a width of 50 - 200 meters and an area of nearly 0.2 km². Reichenkar rock glacier (western Stubai Alps), which has a length of 1400 m, is considered as one of the longest rock glaciers. Structure The surface is covered by a coarse grained debris layer (which is the active layer), underlain by a core of frozen debris and/or sometimes ice. The surface of most of the active rock glaciers is differentiated by some well developed networks of ridges and furrows both longitudinally and transversally. The frontal slope of an active rock glacier is typified by an almost vertical gradient (in the range of 40 - 45°) and is devoid of any vegetation. It is usually composed of fresh and unweathered matter.
[Writer's surname]
5
In the base of some rock glaciers a depression similar to the shape of a spoon gets developed as a result of the melting of huge mass of ice under the upper layer of debris. Temperatures recorded in the debris layer The temperature in the debris layer shows complex behavior. It depends on various factors, especially the weather, the distribution on the basis of grain-size, the thickness of the layer of debris and the core ice inside. As expected, a rapid decrease in temperature can be observed from the surface region to a depth as less as 150 cm. Generally, the minimum temperature can be recorded between 10-12 in the evening and maximum temperature between 6-12 in the morning. Temperatures recorded at the base of the winter snow cover (Below the Surface) As a thick snow layer acts as an insulating layer, temperature at the base of a winter snow cover gets mainly influenced by only the heat flow from underlying ground ice. That is why temperatures at the basal part do not show temperature variations on daily basis. The recorded temperature in active rock glaciers is usually found to be below -3°C (a normal indication of permafrost), while on ground free from this phenomenon it is notably higher i.e. in the range of -0.3°C and -1°C. Hydrology Temperature of the melted water gushing out in the form of springs from active rock glaciers is generally very low and is recorded in the range of 0.4-0.9°C. This shows that this spring water was in direct contact with ice while passing through the rock glacier. This discharge of water from active rock glaciers is affected strongly by seasonal and diurnal variations. It is controlled by several factors such as the thickness of the winter snow layer, the whole size of rock glacier and the drainage area, the existence of one or many cirque glaciers in drainage area, the layer thickness and the grain size of the debris of the
[Writer's surname]
6
active layer, the groundwater abundance or scarcity and the general weather during the melt period, especially summer thunderstorms, resulting in a noticeable seasonal and diurnal variations. The water released from these springs may be a result of many independent phenomena. Like it may have come from snowmelt or melting of permafrost or glacier ice or atmospheric precipitation in summer may also be a reason of it.
Fig. Debris-ice components in mountainous area with suggested terminology for the main features and alternative terms in parentheses. After Martin and Whalley (1987), Humlum (1988), and Hamilton and Whalley (1995). (Source: Whalley, W. B., and F. Azizi, 2003) Electrical conductivity of the water, during cold weather periods, is generally low as the water is mostly derived from snow/ice and/or precipitation, it gets high in autumns when melting is low and the discharge is normally consist of groundwater. An interesting discovery in the modern age was the proof of presence of similar to earth rock glaciers on the surface of Mars. A lot of research is still needed before someone
[Writer's surname]
7
can put something conclusive about this discovery as they can, until now, best be described as “rock glacier-like features”. (Malin, M. C., et al., 2001) Rock Glacier Formation Geologists, over the years, have proposed several hypotheses about rock glacier formation. Despite all the difference of opinions all the hypotheses agree on one thing i.e. a necessity of prolonged cold conditions (same conditions as that of permafrost). Supposing if a glacier is large enough, it can maintain its own internal microclimate. There have been three main models of rock glacier formation which are proposed and discussed in detail by Whalley and Martin (1992), namely a permafrost origin, a glacierderived origin, and a mass-wasting (landslide) origin. The first two are based on the creep of ice while the third (the most likely one) may involve, but does not need, the presence of ice. These models are briefly discussed below: Permafrost Model The permafrost model for rock glacier formation is based on the ideas of Wahrhaftig and Cox (1959) and has been propagated in particular by Barsch (1996) and Haeberli (1985). The “congelation” ice formed from freezing water (either by ice segregation or water injection under pressure). An important requirement is an average annual air temperature of, at most, -1.5°C. This thermal condition implies a “zonal” occurrence of rock glaciers and this attribute has led to the use of rock glaciers as being indicators of permafrost, both present and relict (Barsch, 1996). The presence of any glacier ice which plays a part in the formation of rock glaciers is generally disputed by adherents to this model. The literature often implies that rock glaciers necessarily have a permafrost origin. Glacial Model
[Writer's surname]
8
The glacial model (for a comprehensive review, see Whalley and Martin, 1992), relies on the preservation of a thin (generally <50 m) body of ice by an insulating weathered rock debris layer. The ice is considered to be derived from glacial, i.e., “sedimentary” sources. The thin ice creeps, giving a typically low velocity and the debris preserves this in an otherwise ablation-dominant environment. The controls on maintaining this buried ice are thus related to thickness of debris cover as much as local climate (measured by, e.g., degree-day estimates). As such, they are “azonal” features and cannot be used to delimit temperature regimes such as the presence of permafrost. Landslide Model The landslide, or “catastrophic,” model (Johnson, 1974, 1984) has used similarity of topographic form to suggest that rock glaciers may be derived from rapid landslides/rock avalanches (Bergsturtz or Sturtzstroms) (Whalley, 1976; Whalley and Martin, 1992). These will generally be forms which do not flow after emplacement. However, it has been recognized that some Bergsturz have fallen on retreating/down-wasting glaciers and so have produced “instant” rock glaciers. This is a variation of the glacier ice cored model rather than the landslide model (Whalley, 1976). In the case of fossil rock glaciers, it may not be easy or possible to distinguish between these origins. When a pile of debris at the basal part of a cliff (also known as talus) gets saturated with freezing and liquefying water, it may tend to slowly move just like a glacier (normally the mass-wasting movement is slower and less noticeable as it usually has a very low angle of repose). Whereas in true glacier movements as a result of the pressure from the weight of the ice pack itself compressing the underneath lying ice until it becomes plastic and starts flowing slowly, in this particular kind of rock glacier it is mainly the melting of the ice that results in that flow. It can be also be compared with solifluction, however the rocks involved here provide the flow a much steeper angle of repose, depicting the appearance of a true
[Writer's surname]
9
glacial flow. Usually in these types of cases flow may sometimes be aided by the glacier standing directly on top of permafrost (which does not absorb the melting water). Conclusion Interpretation of many Martian surface forms has, currently, to be done by comparison with terrestrial landforms. For “rock glaciers” this seems to be particularly troublesome. Unfortunately, not only is there a lack of agreement on the terrestrial forms and their significance but there is also little about the nature or volume of any ice bodies found. For example, a glacial model for a rock glacier implies that it is likely to contain much more ice than if a permafrost model was applicable. Conversely, creep of a deforming body containing little ice may take place over many thousands of years. That ice is a major, probably the only, reason for flow in these debris masses seems to be clear but the identification of the volumes and their location is difficult on Earth and Mars. Modeling of ice bodies under Martian temperatures (Colaprete and Jakosky, 1998) and FE modeling, of rock glaciers and protalus lobes with variations of the component mixtures (Azizi and Whalley, 1995) shows a way forward. It is probably necessary to combine the flow model with suppositions of where the ice may be located. Not only would this apply to various forms of ice-rock debris composite but might also be used to test the origin of the water source. However, there are still difficulties in knowing which constitutive equations to use (ice-rock mixture ratios as much as temperature) let alone the actual thickness of the body and ice location. Effective shear stresses acting on deforming ice requires knowledge of both the thickness of material, deforming and rigid, at any location. There is still a paucity of information in terrestrial rock glacier systems which relates topographic features to rheology.
[Writer's surname] 10 Ground Penetrating Radar (GPR) is possibly the end of arguments about the internal structure of these rock glaciers (Degenhardt, John J. Jr. et al. 2002). With the advancement in science as a whole and particularly in the field of geology we can foresee a time when, like so many other phenomenon of nature, the mystery of the formation of rock glaciers will also be solved.
Works Cited Brenning, A. Statistical Estimation and Logistic Regression Modeling of Rock Glacier Distribution in the Andes of Santiago, Central Chile. Geographisches Institut, Humboldt–Universität zu Berlin. Burger, K. C.; Degenhardt, J. J.; Giardino, J. R. Engineering geomorphology of rock glaciers. Geomorphology. Volume 31, Number 1, p. 93-132. Elsevier. December 1999. Davis, T. Neil. Rock Glaciers. Article #251. Alaska Science Forum. September 7, 1978. Degenhardt, John J. Jr. et al. The Internal Structure of Rock Glaciers and Geomorphologic Interpretations: Yankee Boy Basin, CO, USA and Hiorthfjellet and Prins Karls Forland, Svalbard. The Geological Society of America (GSA). Paper No. 115-4. 2002 Denver Annual Meeting. October 27-30, 2002. Giardino, J. R., J. F. Shroder, et al. Rock Glaciers. London, Allen & Unwin. 1987.
[Writer's surname] 11 Goolsby, Jimmy Earl. East rock glacier of Lone Mountain, Madison County, Montana. Montana State University. Bozeman, Montana. June 1972. Ikeda, A. Combination of Geophysical Methods for Measuring the Structure of Rock Glaciers. American Geophysical Union. Fall Meeting 2007. Johnson, P. G. "Rock glacier types and their drainage systems, Grizzly Creek, Yukon Territory." Canadian Journal of Earth Sciences. Issue 15, p. 1496-1507. 1978. Johnson, Peter G. Mass Movement of Ablation Complexes and Their Relationship to Rock Glaciers. Geografiska Annaler. Series A, Physical Geography, Vol. 56, No. 1/2, pp. 93-101. Blackwell Publishing on behalf of the Swedish Society for Anthropology and Geography. 1974. Konrad, S. K., N. F. Humphrey, et al. "Rock glacier dynamics and paleoclimatic implications." Geology. Volume 27, Number 9, p. 1131-1134. 1999. Leysinger Vieli, G. J. M. C.; Gudmundsson, G. H. Evolution of rock glaciers and alpine glaciers: A model-model approach. Proceedings of the 8th International Conference on Permafrost, Zurich, Switzerland. 2003. Malin, M. C., et al., SW Candor layered floor terrain, in NASA Planetary Photojournal, image M2101824, NASA, Washington, D. C. 2001. Potter Jr., N. Ice-cored rock glacier, Galena Creek, northern Absaroka Mountains, Wyoming. Geological Society of America Bulletin, Issue 83, p. 3025-3057. 1972. Steig, Eric J.; Clark, Douglas H.; Potter Jr., Noel; Gillespie, Alan R.. The geomorphic and climatic significance of rock glaciers. Geografiska Annaler: Series A, Physical Geography. Volume 80, Number 3-4, p. 173-174. 1998.
[Writer's surname] 12 Whalley, W. B., and F. Azizi, Rock glaciers and protalus landforms: Analogous forms and ice sources on Earth and Mars, Journal of Geophysical Research. 108(E4), 8032, doi:10.1029/2002JE001864, 2003. Whalley, W. B.; H. E. Martin. "Rock glaciers:II models and mechanisms." Progress in Physical Geography. Volume 16, Number 2, p. 127-186. 1992.
