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I am very new to the study of the cryosphere. I was looking at the GLIMS inventory for glaciers and observed red patches as shown below which the legend mentions the red patches as internal rocks. In my limited understanding internal rocks are frozen debris that have hardened over many years ? Is this correct ? Secondly, how are these rocks inside the glacier determined ?

enter image description here

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    $\begingroup$ the rocks has come loose and are transported by the ice in the same way as a river transports rocks.it is expected that you have searched for an answer to your question before asking here.to learn about how rocks are transported by ice please take a look here en.wikipedia.org/wiki/Moraine and here bbc.co.uk/bitesize/guides/zxn87hv/revision/3 $\endgroup$ Dec 13, 2021 at 5:49
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    $\begingroup$ I think "internal" is meant to signify that there are rock outcrops within the glacier boundary not rock internal within the glacier ice. This measn the area of the glacier boundary should be reduced by the outcrop area to yeidl the glacier area. Remeber that GLIMS is a remote sensing product and can only record what is visible on the surface. $\endgroup$ Dec 13, 2021 at 11:17
  • $\begingroup$ @PeterJansson Thank you so much for your explanation. Could you kindly guide me to any literature that mentions the glacier area determination by removing the internal rocks? $\endgroup$
    – user157522
    Jan 19, 2022 at 5:15
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    $\begingroup$ @user157522, I do not know of any specific paper but the GLIMS site glims.org should provide sufficient information and they also list scientific publications relating to the inventory. $\endgroup$ Jan 19, 2022 at 12:26

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Although glacier data is acquired via satellite, a lot of painstaking manual interpretation must, among many other things, separate glacier from snowfield, simple debris field from debris covered glacier. All of these qualifiers go into the GLIMS GIS database that makes it possible to measure real glacier behavior over time, without actually having to get on the glacier itself every summer with a tape measure and notepad.

When manually delineating glacier outlines (AKA polygons) a GLIMS analyst may include rock outcrops that are entirely within a single glacier. As per p.8 of GLIMS Analysis Tutorial:

To create an outline that conforms to the above definition, one should create one polygon (or series of segments) that circumscribes the entire glacier. Internal rock outcrops are excluded by producing outlines around them and labeling those outlines as internal rock. This can be done simply in GLIMSView, or can be done with other tools. In the resulting “segments” shapefile, the “category” attribute should be “intrnl_rock” for internal rock segments. Internal rock polygons should be separate polygons (or collections of segments), not sub­parts of multi­part polygons. Other separate polygons can be used for supraglacial lakes or debris cover. Glacier outlines should be of glacier boundaries, not basin boundaries.

"Internal rock" polygons should only be
included if the outcrop is completely internal to
one glacier.

Figure 2: "Internal rock" polygons should only be included if the outcrop is completely internal to one glacier.

In your example, the red "internal rock" appears to be entirely surrounded by a single glacier, not uncommon where a steep rock face on a mountain is entire surrounded by ice.

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  • $\begingroup$ Good that you added onto my comment! $\endgroup$ Dec 19, 2021 at 20:45

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