Glacial floodplains
a) Broad glacial floodplain in front of an icecap. Photo: Winfried Dallmann / Norwegian Polar Institute
b) Where glacial floodplains emerge from a valley and meet the coast, a river delta develops. Photo: Winfried Dallmann / Norwegian Polar Institute
Glacial floodplains stretch from the front of a glacier to the coast. They occur either in the bottom of U-shaped valleys ahead of valley glaciers or form wide plains at the front of the icecap. Where glacial floodplains emerge from a valley and meet the coast, a river delta may form. A floodplain (image b) consists of stones deposited by the glacial rivers, sometimes with sand and clay areas deposited from slow-flowing or stagnant water following the spring flood or rain. The river beds have many bends that meander slowly down, branch extensively and gradually change their main course. Glacial floodplains are in constant change.
Where glacial floodplains emerge from a valley and meet the coast, a river delta (image a) develops, if the material deposition is greater than the tide and coastal currents can remove. A characteristic river delta has a semi-circular form encircled by a raised beach. Within the delta plain, the glacial river branches in a fantail. The surface consists of stony ground with sand surfaces between the river courses.
On parts of floodplains and deltas that have been dry for a long time, soil is created and vegetation grows. This can gradually cover large areas.
Moraines
Moraine is a collective term for unsorted eroded material deposited by a glacier. Moraines contain a mixture of all particle sizes, from clay up to large blocks. Depending on where relative to the glacier the moraine is deposited, different land forms will be created. In Arctic regions, most of them have ice cores.
a) Push moraines. Photo: Otto Salvigsen / Norwegian Polar Institute
b) Ice-cored moraines. Photo: Otto Salvigsen / Norwegian Polar Institute
c) Lateral and medial moraines. Photo: Winfried Dallmann / Norwegian Polar Institute
d) Medial moraines. Photo: Winfried Dallmann / Norwegian Polar Institute
e) Medial moraines. Photo: Winfried Dallmann / Norwegian Polar Institute
f) Ground moraines. Photo: Winfried Dallmann / Norwegian Polar Institute
g) Push moraines/lateral moraines: Moraine material remains along the ground after the ice has melted away. The land surface is irregular, more or less hilly, and often has many small water and mud holes and river beds.. Photo: Winfried Dallmann / Norwegian Polar Institute
Terminal moraines are piled up and pushed forward by the glacier terminus and occur as mounds ahead of the glacier. In narrow valley glaciers, they may have a crescent form seen from above. There may be several ridges of terminal moraines in front of the glacier terminus that reflect various minor forward thrusts during the retreat of a glacier (push moraines, images a, g).
Lateral moraines (image c) are ridges of moraine deposits pushed out to the side of a glacier. They appear as tall, extended ridges between the ice and the valley side.
Medial moraines (images c, d, e) are formed between two ice flows when two glaciers meet, or behind an obstacle. Once the ice has gone, they often remain as long, thin and tall ridges.
Ground moraines (image f) are moraine deposits left lying along the ground after the ice has melted. They have an irregular, more or less rolling, surface, often with many small water and mud holes and river beds (image g).
Moraines in Svalbard often have a core of relatively clean ice (ice-cored moraines, image b).
Pingos
Pingos are rounded knolls, mostly on plains and valley bottoms, from a few metres to more than 40 metres high. They have an ice core and are formed when water under pressure forces itself through holes or cracks in the permafrost.
Photo: Winfried Dallmann / Norwegian Polar Institute
Photo: Winfried Dallmann / Norwegian Polar Institute
Photo: Winfried Dallmann / Norwegian Polar Institute
Depending on where the pingo is formed, there may be sand, gravel, soil or continuous rock strata on the surface. Water may flow out from springs in pingos, or from a network of cracks in the permafrost.
In Svalbard, pingos occur singly in many valleys near the coast and on strandflats from north to south, but larger collections are only common in the major valleys of central Spitsbergen that have a milder climate (Adventdalen, Reindalen, Kjellstrømdalen).
Patterned ground
Patterned ground is a collective term for surface structures in loose material (regolith) showing geometrical patterns. The structures are formed through the freezing and thawing of the upper layers of the permafrost.
Patterned ground. Photo: Winfried Dallmann / Norwegian Polar Institute
Patterned ground. Photo: Winfried Dallmann / Norwegian Polar Institute
Patterned ground. Photo: Winfried Dallmann / Norwegian Polar Institute
Patterned ground. Photo: Winfried Dallmann / Norwegian Polar Institute
Patterned ground. Photo: Winfried Dallmann / Norwegian Polar Institute
Patterned ground. Photo: Otto Salvigsen / Norwegian Polar Institute
As the ice contracts, cracks occur which are then filled with water, which in turn freezes and expands. As it freezes, the ice expands and causes the surface to bulge up.
In the ideal form, the bulges will be circular or hexagonal in shape so as to make most efficient use of space. Inhomogeneities in the loose material produce deviations from this form. On sloping terrain, the structures will be elongated. On very sloping terrain, they often appear as a striped pattern.
The larger the stones in the permafrost, the faster heat is conducted into or out of the underground, ensuring different freezing and thawing rates, depending on the particles’ size. This gradually causes the material to be sorted by size and raised to the surface.
Depending on these factors, stone circles, stone polygons, stone stripes, or unsorted polygonal or striped patterns of cracks are formed in the ground. The vegetation adapts and conforms to the patterns.
Ice wedge polygons are large polygonal structures (10-80 m) that are best viewed from afar – from high ground or from an aircraft.
Mudflows
Mudflows are mostly triggered in the steep upper sections of mountainsides, where meltwater, or the result of heavy rainfall, causes clay-rich rock layers to swell up so that they – along with the overlying layers – become unstable and slide down.
Mudflows. Photo: Winfried Dallmann / Norwegian Polar Institute
Mudflows. Photo: Winfried Dallmann / Norwegian Polar Institute
The greater the height difference and the steeper the slope, the faster the flow. Speeds of up to 180 km/h have been measured at the valley floor under the mountainside. Such slides have caused many fatalities.
The mudflows move through gaps or depressions. Stones of all sizes up to large blocks float in water-saturated clay. The large stones are pushed out to the side where they gradually form mounds, while the fine-grained material floats in a central channel. It is not possible to walk over a newly-formed mudflow deposit until several days have passed and the clay has settled.
Rock glaciers
Rock glaciers are created in scree (talus) under steep mountainsides. These unsorted landslide deposits consisting of land, clay and stones are frozen due to the permafrost.
Rock glaciers. Photo: Otto Salvigsen / Norwegian Polar Institute
Rock glaciers. Photo: Winfried Dallmann / Norwegian Polar Institute
As in the formation of patterned ground, sorting processes occur in the permafrost, and permafrost layers can be formed that are no longer supported by intermingled stones. The ice will then begin to flow down the slope like a glacier and carry the stone material with it.
The movements are of a few centimetres a year. Gradually, a typical tongue-like shape with a curved surface is formed, with a small depression at the top of the tip and a steep front.
The largest rock glaciers in Svalbard are at Prins Karls Forland with terminus heights of up to 50 m.