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L79 Glacial Polish on Columnar Basalt, Devil's Post Pile National
Monument, California, USA.
Position:
N39° 40' 15''
W120° 52' 54''
Elevation:
6000'
Image format:
35mm
GLACIAL POLISH ON COLUMNAR BASALT
This image speaks volumes about the geological history of a small
part of California. About 100,000 years ago there was a volcanic
eruption of a lava called BASALT.
Basalt is a hot, runny lava that erupts at around 1000°C . This
type of lava will flow quite freely away from the site of eruption
(FLOOD BASALT is a term that often describes this type of event).
Eventually, within a few miles/kms of the VENT the flow will stop
as the basalt cools and thickens.
In this case there is no sign of the original vent from which
the lava erupted but it would have been in the near locality.
All that is left is this superb body of cold, solidified basalt.
The lava shrinks as it cools and forms the distinctive polygonal
shapes that are quite common in nature (see the Image Trail below)
Image Trail:
Glaciation : L8 L9 L65 L66 L80
Polygonal shapes : L25 L80 |
