Tussock and Frost Hummock Cross-section Photos

Tussocks are compact tufts of organic material formed by some species of sedges and grasses. Tussocks are typically about the size of a soccer ball, but range in size from a softball to a small beach ball. Frost hummocks are formed from differential frost heaving of soil.

Cross-section of frost hummock on a pingo on the central Beaufort Coastal Plain, AK. Note the convoluted and broken soil horizon caused by frost heave.
Frost hummocks in the alpine in Lake Clark National Park and Preserve covered in moss heather (Harrimanella stelleriana), AK.
Cross-section of frost hummocks in Lake Clark National Park and Preserve, AK. Note the broken and undulating horizons caused frost frost heave.
Cross-section of an Eriophorum vaginatum tussock on the Chukchi Coast, AK. Note the tussock is all organic material, with brownish mineral soil beneath.
Cross-section of tussock from the northern foothills of the Brooks Range, AK. The tussock itself is all organic matter consisting of dead stems and leaves of tussock cottongrass (Eriophorum vaginatum). The common name is a misnomer as this species is actually a sedge.
Tussock Hugger! Tracy hugs a tussock of unusual size in the National Petroleum Reserve, northern Alaska.

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