Periglacial Geomorphology A Useful Glossary A Useful Glossary

Air temperature <-6°C Albedo follows cycle – affects surface T Snow cover drives albedo Result = surface and subsurface temps! The periglacial environment

Permafrost distribution Continuous -5 to -10 °C Mean annual average temperature Discontinuous –In coastal Greenland Sporadic –Mountains

Permafrost mean annual T o below 0 o C Surface changes are in “Active Layer” –thin soil layer of soil over the permafrost, seasonally thaws Permafrost: soil at or below the freezing point of water 0 °C (32 °F) for 2 or more years.

Needle Ice Needle ice forms at the beginning of the freezing season, before the freezing front has penetrated very far down into the active layer and there is no soil overburden to lift as a frost heave

Frost Heaving Soils containing water that expands when frozen, moving the soil upward.Soils containing water that expands when frozen, moving the soil upward. Large scale palsa formed by winter frost heave, then cut by summer meltwaterLarge scale palsa formed by winter frost heave, then cut by summer meltwater

A chaotic pattern believe to be due to periglacial Frost Heave of the unconsolidated Bridgeton Fm, near Hammonton, NJ. Photo courtesy of. R. Kroll.

Periglacial - peripheral to glacier Tundra & intense frost - often permafrost U-shaped Valley Permafrost underlies ~24% 0f land, mostly northern Alaska, Canada, Russia, China Top 1-2 meters is subject to seasonal thaw Palsa: low frost heaves containing frozen ice lenses. Palsas in peat moss Here frost heaved peat hummocks Palsas Tundra: biome where plant growth hindered by low temperatures and short growing seasons. Plants: dwarf shrubs, sedges and grasses, mosses, and lichens.

Ice Wedges Cracks formed by a narrow piece of ice that extends downwards into the ground up to several meters. Once temperatures reach -17 o C or lower, the ice expands to form cracks in the surface known as ice wedges. Ice wedges connect to form ice wedge polygons.

Ice Wedge Casts Active layer ice melts in summer, water warms ice wedge in permafrost, hole fills with soil from active layer

An Ice Wedge cast near Hammonton, NJ. Photo courtesy of R. Kroll

Patterned Ground Surrounding Melt Lakes Sorted nets As water freezes, it expands Freezing of groundwater forces larger stones upward Wet soils flow underneath larger stones, keeping them up. Soils are water saturated, large rocks are not, wet soils freeze and expand, push larger stones away from the center

Patterned Ground on Mars Figure 2. Different examples of high- latitude patterned ground on Mars. (C) 200 m wide polygons formed by networks of cracks inside a crater MOC (type LT). MOC image E (64.7N, 292.9W).

Frost Mounds: Pingoes A pingo rises from the Arctic plain in far northern Canada, near Tuktoyaktuk, NWT. Image: Charlie Paull © 2003 MBARI Pingos : water confined underground freezes, buckles the ground upward. Open stage

“At least some of the vast amount of water that carved Mars’ fluvial and flood morphologies is still present in the form of ground ice. One of the most intriguing forms of ground ice is the Pingo, a type of massive ice-cored mound found in periglacial and previously glacial terrains on Earth” Mars Pingoes

Thermokarst Characteristic landforms from thawing of ice-rich permafrost or the melting of massive ice blocks. It is characterized by an irregular topography, with irregular pits and depressions develop by thaw settlement

Solifluction Slow downslope movement of alternately dry and water saturated sediment

Gelifluction Gelifluction lobe on south slope of Låktatjåkka, 1400m asl, (Jan Boelhouwers) Skip 314 right to 318 left.

High Latitude crater slope flow on Mars Fig. 7. (a) CTX image (B01_010077_2520_XN_72N015 W) showing the crater 1 study areas as solid boxes. HIRISE coverage is shown as dotted boxes. (b) Sub frame of HiRISE image (PSP_010077_2520) showing widespread, non-sorted lobes at north-east facing wall. (c) Lobe features alongside a braided channeled gully. (d) Close up of lobe features; note the densely fractured surface on the treads. (e) Close up of stripes, white arrows indicate coarse bands. Image credit: NASA/JPL/MSSS and NASA/JPL/UoA.

Frost scaling = spalling Frost Wedging Polar regions: Strong Mechanical Weathering Very slow chemical weathering Thermal Expansion & contraction

Block Fields = Felsenmeer (CO Front Range) Frost Shattered Granite Bedrock Frost Shattered Granite Bedrock Frost Wedging, Spalling

Rock Glaciers Northwest Territories, Canada Northwest Territories, Canada Park Range, CO Park Range, CO All known rock glaciers are derived either from glacial debris downvalley from an active or inactive glacier, or from avalanche debris, sliderock, or colluvium on a valley wall" Bloom, p. 319 Rock Glacier angular rock debris usually frozen in interstitial ice

Rock Glacier Three types Glacial: created by the recession of debris covered glaciers Periglacial: continuous freezing occurring within a talus lobe Landslide: does not require the presence of ice