Susan. Lecture 5 Flashcards
What are the characteristics of permafrost aquifers?
K of frozen ground is lower than unfrozen
Frozen ground is a low conductivity aquitard
Unfrozen active layer is a seasonal, thin, perched aquifer but on freezing can become low k aquitard
Re/discharge limited to gaps in ice Extraction from these gaps or wells drilled below permafrost
What is meant by the term ‘superpermafrost water’?
The permafrost layer is coupled with the active layer
What is intrapermafrost water?
The zone of perennially frozen soil, can be up welling and down welling depending on whether being fed by sub or superpermafrost waters respectively.
What is subpermafrost water?
Found below the permafrost, can be at considerable pressures, conditions are quite stable
What is a talik?
Interconnected areas of unfrozen ground in permeable ground within the permafrost which functions as areas of groundwater flow. Upwards flowing - seepages and springs Downwards flowing - aquifers
Describe the energy balance in taliks
If heat not supplied from warmer recharge then water in pores will freeze and aquifer will no longer exist. Total energy available in the water (heat) must balance that being lost (conduction) to the surrounding permafrost. Energy is also released in freezing (latent heat) of water at the edge of the talik, that allows the bulk of the water to be maintained as liquid water.
Dome Creek Valley in Fairbanks, Alaska is an unconfined aquifer and no water can be extracted from the frozen fluvial deposits. Why then is an artesian flow possible here?
The bedrock is confined by the base of the permafrost. Its hydraulic heads rise above the ground surface and this makes artesian flow possible.
What causes crustal scale pore-fluid flow?
Discuss carbonate aquifers
Limestones porosities range from 20% in coarse blocky limestones to >50% in chalk.
Crystal lattice of dolomite is ~10% < limestone, dolomitisation will increase porosity and permeability.
Depth of burial influences closing of primary porosity adn induction of mineral growth and crystallisation reducing space and permeability.
Borehole productivity can vary depending on whether productive fractures are intersected or not.
What is a flow corridor?
The area of a saturated zone where the main quantity of groundwater is moving relatively quickly along the local hydraulic gradient regardless of the proportions of the enlarged fissure-flow
Give three reasons why the K value of volcanic aquifers is highly variable?
Variation in rock type, manner of rock extrusion and deposition
Describe the aquifers in igneous and metamorphic rocks
Unfractures, porosity is low (<2%) and in the form of small unconnected pores.
Matrix ‘K’ are normally very low.
Aquifer properties depend on extent of fracturing giving often moderate conductivities but low storage coefficients.
Weathered saprolite above basement aquifers may be permeable with high porosity (40-50% specific yield of 15-30%)
Where is the highest k value found in basalt aquifers?
Parallel to flow as columnar jointing makes it strongly anisotropic and interflow lavas are often composed of coarse alluvium.
