Mud boils and frost polygons on different surficial sediment types
Location:
Nunavut,
Canada;
NTS
55L Kaminak Lake;
ca.
62° 21'N, 95° 10'W
This
photograph shows a landscape dominated by mud boils and polygonal frost
cracks, just north of Kaminak Lake. This image illustrates very well
the specificity of different types of patterned ground to different surface
sediment types. The documentation of this specificity formed the basis for
delineating surficial geological units on 1:125,000 Geological Survey of
Canada maps of surficial materials made in the late 1970's and early 1980's.
In this case, mud boils are exclusively developed on clayey till and marine
silty clay of the post glacial Tyrrell Sea, which was about 100 m deep here
at its maximum extent, 6,200Ø years ago. The circular mud boils are 2 to
3 m in diameter, and the frost polygons are 15 to 20 m in maximum dimension.
The frost polygons are developed on more than 1 m of fibrous peat, which
thaws to depths of less than 40 cm, even in the warmest summers. The peat
occupies a flat, low, poorly drained area and may be underlain by the same
inorganic sediment that is ornamented by mud boils where it is well-drained.
It is the peat, with its shallow frost table
(less than 50 cm during the height of the thaw season), that develops where
drainage is poor and creates the conditions for preservation of frost cracks/polygons.
Note that the mud boils in the foreground are white, which indicates that
they are active, and have extruded mud in the past few years. For a more
complete description of processes and terminology, see the discussion under
image 0240 . Similarly contrasting patterned
ground can be seen in images 0066, 0068,
0069, 0093,
0100, 0229,
0230, 0236.
Photo by Dr. A. N. Boydell
Updated 08/28/2009 CAB