12 - Pingo's & Palsas

Palsas: Cryosuction: caused by  negative pressure of freezing ground. Permafrost mound with a core of alternating segregation ice and peat/mineral soil compound. absence of snow allows further/deeper frost penetration that increases the growth of palsa. the snow absence can be caused by multiple factors, not only climate but also tree cover & other veg as well as wind blowing the snow off of the top of the palsa. Lithalsa: a palsa without the superseding peat layer. Growth is primarily due to cryosuction of surrounding moisture to the palsa that stimulates growth via ice segregation. Palsa's grow gradually over time and can persist for decades.

Frost Mounds: Perennial, Intrapermafrost, ice-cored hills and can only grow and exist in a permafrost environment (although relict mounds can exists in different climates. All pingo's are cored by massive ice or ice rich sediments, the first stage of decay is the melting of the core and subsequent collapse of the mound. hydraulic: open system, gets pressure from topographic gradient. Hydrostatic: closed system, Pore water expulsion beneath aggrading permafrost causes necessary pressure for pingo formation.

Hydraulic:Open system whereby intra or sub permafrost groundwater reaches the surface under sufficient pressure.structural weakness controls the taliks necessary for hydraulic pingo formation. It is suggested that a certain amount of segregation ice is required on top of the artesian (from aquifer) injection of water.Hydrostatic: Clsoed system, caused by permafrost aggradation underneath the bottom of drained lakes where the soil is saturated and sandy. often pulsating patterns can be observed due to the build up of pressure of ice lenses in a growing pingo then release of pressure. When the lake is recently drained the leftover moisture freezes and pore ice formes heaving the relict lake bed upwards.

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French Ch 6 selection