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  • #16
    Originally posted by MarkV View Post
    Glaciers can move through basal sliding "Another process by which glaciers move is basal sliding. With basal sliding, we see the entire glacier moves as a single unit due to melting at its base. Pressure at the base of the glacier causes a thin layer of ice to melt. This reduces friction, allowing the entire glacier to slide downslope" Recent research published by the University of Maine have indicated that the speed of slide in a warming period can increase by a factor of up to three
    All glaciers move via basal sliding. Basal meltwater enables this process by lubricating the ice-rock contact.

    Basal melting is due to pressure (pressure melting point) or a geothermal source (heat flow from the Earth's interior). Pressure-driven basal melting can only accelerate if the glacier is accumulating ice, increasing basal pressure. As a glacier melts and thins, basal pressure is reduced, lowering the pressure melting point.
    Last edited by The Doctor; 07 Sep 15, 09:09.
    Watts Up With That? | The world's most viewed site on global warming and climate change.

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    • #17
      The global glacier mass balance since 1960, reported to the National Snow and Ice Center and the World Glacier Monitoring Service:



      Mountain glacier mass balance changes since 1970 as represented by Dr. Robert Rhode:



      - Nearly all glaciers surveyed in Alaska are melting. Thinning rates in the last 5 to 7 years are more than twice those seen in previous years. Half of the water flowing into the oceans, globally, due to melting glaciers, is a result of melting in Alaska.

      - The northern Andes contain the largest concentration of glaciers in the tropics, but these glaciers are receding rapidly and losses accelerated during the 1990s.

      - Glacier melting has accelerated in the European Alps since 1980, and 10 to 20% of glacier ice in the Alps was lost in less than two decades. Half the volume of Europe's Alpine glaciers has disappeared since 1850. By the end of this century, half of those left will have gone as well.

      - Tropical glaciers in Africa have decreased in area by 60% to 70% on average since the early 1900s.

      - The vast majority of all Himalayan glaciers have been retreating and thinning over the past 30 years, with accelerated losses over the last decade.

      - The tropical glaciers in the Pacific have retreated, although in New Zealand some glaciers grew due to increased precipitation.

      - Arctic glaciers have been receding, with the exception of Scandinavia and Iceland where increase in precipitation resulted in glacier growth. Greenland alone contains 12% of the world's ice; entire portions of the Greenland ice sheet appear to be sliding towards the sea.

      - In Antarctica the centre of the continent is currently cooling so it won't be melting soon. However, coastal glaciers and ice sheets in the Antarctic are melting. The melting of ice sheets and ice shelves that sit on top of land, will result in higher sea levels.
      http://wwf.panda.org/about_our_earth...acts/glaciers/

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      • #18
        Originally posted by BobTheBarbarian View Post
        The global glacier mass balance since 1960, reported to the National Snow and Ice Center and the World Glacier Monitoring Service:

        [IMG...tps://upload.wikimedia.org/wikipedia/commons/e/e5/Glacier_Mass_Balance.png[/IMG]

        Mountain glacier mass balance changes since 1970 as represented by Dr. Robert Rhode:

        [IMG...https://upload.wikimedia.org/wikipedia/commons/9/93/Glacier_Mass_Balance_Map.png[/IMG]



        http://wwf.panda.org/about_our_earth...acts/glaciers/
        Would it be better if the globally averaged glacial mass balance was moving in the opposite direction?

        What was it doing before 1955?

        What was it doing from 2000 BC up until the mid 1800's?

        What was it doing from 8000 BC up until 2000 BC?
        Watts Up With That? | The world's most viewed site on global warming and climate change.

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        • #19
          Originally posted by BobTheBarbarian View Post
          The global glacier mass balance since 1960, reported to the National Snow and Ice Center and the World Glacier Monitoring Service:

          [IMG...tps://upload.wikimedia.org/wikipedia/commons/e/e5/Glacier_Mass_Balance.png[/IMG]

          Mountain glacier mass balance changes since 1970 as represented by Dr. Robert Rhode:

          [IMG...https://upload.wikimedia.org/wikipedia/commons/9/93/Glacier_Mass_Balance_Map.png[/IMG]



          http://wwf.panda.org/about_our_earth...acts/glaciers/
          Would it be better if the globally averaged glacial mass balance was moving in the opposite direction?

          What was it doing before 1955?

          What was it doing from 2000 BC up until the mid 1800's?

          What was it doing from 8000 BC up until 2000 BC?

          The glaciers at North Cascades National Park have stopped retreating...



          Geologists understand that glacial mass balance is almost always positive or negative. While glacially slow, very few glaciers sit still. Geologists also know that most alpine/valley glaciers in North America are of very recent origin, only dating back to the Mid-Holocene Neoglaciation. Most reached their maximum extent in the 1800's during the Little Ice Age. The “small glaciers” of Glacier National Park, Montana may have not existed during the Holocene Climatic Optimum (HCO). The geological evidence suggests that they formed less than 7,000 years ago as the Earth’s climate began to cool after the HCO...

          History of Glaciers in Glacier National Park


          The history of glaciation within current Glacier National Park boundaries spans centuries of glacial growth and recession, carving the features we see today. Glaciers were present within current Glacier National Park boundaries as early as 7,000 years ago but may have survived an early Holocene warm period (Carrara, 1989), making them much older. These modest glaciers varied in size, tracking climatic changes, but did not grow to their Holocene maximum size until the end of the Little Ice Age (LIA) around A.D. 1850. While they may not have formed in their entirety during the LIA, their maximum perimeters can be documented through mapping of lateral and terminal moraines. (Key, 2002) The extent and mass of these glaciers, as well as glaciers around the globe, has clearly decreased during the 20th century in response to warmer temperatures.

          Climate reconstructions representative of the Glacier National Park region extend back multiple centuries and show numerous long-duration drought and wet periods that influenced the mass balance of glaciers (Pederson et al. 2004). Of particular note was an 80-year period (~1770-1840) of cool, wet summers and above-average winter snowfall that led to a rapid growth of glaciers just prior to the end of the LIA. Thus, in the context of the entire Holocene, the size of glaciers at the end of the LIA was an anomaly of sorts. In fact, the large extent of ice coverage removed most of the evidence of earlier glacier positions by overriding terminal and lateral moraines.

          [...]

          USGS

          “Mapping of lateral and terminal moraines” clearly demonstrates that the maximum extent of the glaciers was reached during the Little Ice Age (LIA).

          Most of the alpine glaciers in Colorado formed after the HCO and reached their maximum extent during the LIA, between 400 and 150 years ago. Most have generally been retreating since the early 1900's...

          [...]

          [T]here have been three small Holocone (10,000 years BP to present) glacial advances termed, from oldest to youngest, Triple Lakes, Audubon, and Arapaho Peak advances. Collectively these minor advances are termed Neoglaciation, and the largest glacier during these advances was only 1.6 km long. The Arapaho Peak advance is local evidence for the Little Ice Age (the popular name for a period of cooling in the northern hemisphere lasting approximately from the 14th to the mid-19th centuries). Most of the glaciers and perennial ice patches in Colorado today are the tattered remnants of these small Little Ice Age glaciers.

          [...]

          LINK

          The glaciers of Mt Ranier National Park may date back to the last Pleistocene glaciation, but they also exhibit a similar variability to those of Glacier National Park and the Colorado Front Range…
          The size of glaciers on Mount Rainier has fluctuated significantly in the past. For example, during the last ice age, from about 25,000 to about 15,000 years ago, glaciers covered most of the area now within the boundaries of Mount Rainier National Park and extended to the perimeter of the present Puget Sound Basin.

          Geologists can determine the former extent of glaciers on Mount Rainier by mapping the outline of glacial deposits and by noting the position of trimlines, the distinct boundaries between older and younger forests or between forests and pioneering vegetation. Geologists determine the age of some of the deposits by noting the age of the oldest trees and lichens growing on them and the degree of weatherring on boulders. Between the 14th century and AD 1850, many of the glaciers on Mount Rainier advanced to their farthest went down-valley since the last ice age. Many advances of this sort occurred worldwide during this time period known to geologists as the Little Ice Age. During the Little Ice Age, the Nisqually Glacier advanced to a position 650 feet to 800 feet down-valley from the site of the Glacier Bridge, Tahoma and South Tahoma Glaciers merged at the base of Glacier Island, and the terminus of Emmons Glacier reached within 1.2 miles of the White River Campground.

          Retreat of the Little Ice Age glaciers was slow until about 1920 when retreat became more rapid. Between the height of the Little Ice Age and 1950, Mount Rainier’s glaciers lost about one-quarter of their length. Beginning in 1950 and continuing through the early 1980′s, however, many of the major glaciers advanced in response to relatively cooler temperatures of the mid-century. The Carbon, Cowlitz, Emmons, and Nisqually Glaciers advanced during the late 1970′s and early 1980′s as a result of high snowfalls during the 1960′s and 1970′s. Since the early-1980′s and through 1992, however, many glaciers have been thinning and retreating and some advances have slowed, perhaps in response to drier conditions that have prevailed at Mount Rainier since 1977.

          [...]

          Mount Rainier National Park Information Page

          The Mt. Ranier glaciers also seem to have beached their maximum Holocene extent during the Little Ice Age.
          Watts Up With That? | The world's most viewed site on global warming and climate change.

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