Moisture and temperature variations drive all arctic and alpine geomorphological processes Flashcards
How is the climate changing + predictions for the future?
(Hassol, 2005)
- Air temperature at high latitudes have been more than twice that of the global average!
- ‘Business as usual’ warming predictions suggests temperatures of between 3-5°C in the Arctic by the end of the 21st century, accompanied by increases in evaporation and precipitation
This means that permafrost temperatures will go up thermokarst activity will increase! (Steedman et al., 2016).
How does moisture effect the nature of material (texture, organic content….) in different ways?
How wet or dry a material is may affect….
Specific heat (how much heat is required to increase a certain volume by a certain amount).
Thermal conductivity (how quickly heat will move through something).
Infiltration and evaporation rates (moisture affects thermal properties)
Albedo (wet = dark)
Generally, how does standing water differ to that of running water?
Running water is warm and so produces thermal erosion (constant replenishing warm relative to frozen permafrost).
Standing water insulates against low air temperatures, and is a heat store (heat isn’t being replenished but will still remain warm, 2-3m deep won’t freeze to bottom, water is densest at 4oC)
Introduce ice wedge polygons as a case study…
…most ubiquitous feature of ground ice in the top 2–3 metres of Arctic permafrost (Christiansen et al., 2016)
…archetypal polygonal patterns that form just below the active layer (Frost et al., 2018).
…particularly sensitive to environmental disturbance that alters the near surface thermal regime (Jorgenson et al., 2006).
…thermal contraction theory of wedge growth, suggested by (Leffingwell, 1915)
How does temperature drive processes in ice wedge polygons?
Cracking in the ice wedge depends on thermal conditions at the top of the permafrost.
How does moisture drive processes in ice wedge polygons?
Linked to temperature is drivers of hydrology- warming conditions = ponded water in the Arctic where ice wedges are exposed, causing them to melt.
This surface water then feeds resilient positive feedback, where thaw settlement produces deeper depressions as the active layer melts deeper beneath the water enabling the storage of even greater volumes of water (Fortier et al., 2006).
= effective heat sinks in the summer months, but due to the high heat capacity of water and thermal conductivity of saturated organic soils relative to dry organic soils (Hinzman et al. 1991), accelerated convective heat flows (Steedman, 2014).
What other two major factors does temperature and moisture affect?
Snow thickness, and vegetation
Kanevskiy et al., 2017
How does vegetation impact?
Vegetation distribution in the Arctic is varied but clearly increasing as the climate gets warmer (Berteaux et al., 2017).
Vegetation is a key determining factor in the overall stability of the permafrost, as the thickness of an organic layer greatly influences stability.
This permits the ground ice to aggrade and heave the surface, therefore lessening surface water depth and soil temperatures
Moisture can also be seen to reduce vegetation…
How does snow affect processes?
Snow is a crucial in determining the ground thermal regime (Zhang 2005).
Johansson et al. (2013), for instance, investigated how increased snow cover impacts permafrost in northern Sweden, finding that as troughs of the ice wedge get deeper, it encourages, like vegetation, insulation through increasing snow entrapment and decoupling the air, contributing to delayed freeze back (Steedman, 2014).
Here, aspect and alpine are the overriding factors influencing geomorphological processes in an Alpine environment, however, the variations in this promote variations in the key drivers- temperature and moisture…
Aspect affects input of radiation.
In northern hemisphere if you’re in a south facing = as much as 4x more incoming radiation.
Aspect affects input of precipitation and snow drifting (wind bearing slopes)
Altitude affects ground temperature
Slope angle controls snow and runoff (steep slope = less now and rapid runoff) (gradual slope = more snow and more infiltration)
Alpine
However other things also influence processes…
What is salt weathering?
What is salt weathering highly dependent on?
Stresses that are formed through salt crystals growth by:
a) Growth within pores and microcrack.
b) Thermal expansion of salt crystals.
c) Swelling through hydration.
The degree of saturation and position with regards to the surface (evaporation).
Alpine
However other things also influence processes…
What does chemical weathering do?
Makes relatively insoluble minerals more soluble.
Reduces strength of bonds making rocks more vulnerable to physical processes.
Alpine
However other things also influence processes…
Chemical weathering
Key factors of cold chemical weathering?
Climate in terms of precipitation (leaching) and temperature (rate of chemical reactions).
However also…
pH of environment (for example, snow and precipitation can be slightly acidic).
Chelation (break up of mineral bonds by acid, for example in organic material).
Alpine
However other things also influence processes…
What is biological weathering?
Micro organisms such as lichen, algae and fungi.
Contribute to surface weathering and vulnerability to chemical and physical weathering by biochemical (detaching grains and flakes) and biochemical (chemical alteration of minerals).
However, this is constrained by temperatures and flora.
