What formation is this

1
What formation is this?
Christian Keller

• Geologial deposits
• at
• Hólar in Hjaltadalur

Compressed verion
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Deserted farm Hólakot
3
The upper end of Hjaltadalur demonstrates the
U-shaped profile of a glacier-excavated valley
4
Note the erosion fans along the sides of the
valley
5
The meandering Hjaltadalsá has cut a free
profile into a low hill, so we can see inside it
6
The upper part of the sediment consists of
coarser and finer material sorted in layers. Thie
indiacetes that they are deposited by water,
running at various speeds Fast water larger
particles. The layers are oblique. This indicates
a violent river where water is moving downhill
fast. Suggestion A glacifluvial deposit
The lower part of the sediment consists of fine,
sorted material in near-horizontal layers. This
indicates a deposition in deeper, calmer
water. Suggestion A glacifluvial deposit either
in the sea or in a lake
7
The glacifluvial layers have been cut through by
running water creating a V-shaped notch. It
suggestss the formation at this point was above
water. The notch was later filled with finer
material.
8
Above the notch, there are near-horizontal
deposits. A white layer near the top is
a tephra layer, possibly Hekla 3000
9
On top of the deposits are large stone
blocks. Their edges are only slightly rounded
(small picture). They must have been left by a
glacier overrunning the older deposits.
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• Rocks tell a story
• Sharp edges (far left) tell of a recent, local
  break-off
• Slightly modified edges (mid left) indicate
  some erosion
• Heavily rounded edges (mid right) indicate
  serious
• moraine activity
• Rounded stones (far right) indicates river
  tumbling