Geomorfologi I: Vittring och massrörelse

Vittring Alla processer som förorsaka bergrund/bergart att disintegrera fysiskt och bryta ner kemisk

Vittring Fysiskt/mekaniskt vittring Kemiskt vittring Berggrund sprickas och brytas Kemiskt vittring Bergart mineraler blir kemisk transformerad Regolit/vittringsjord: lager av jordart vid jordytan som resultat av vittring av underliggande berggrund.

Fysiskt/mekansisk vittring Produceras material direkt från berggrund Inkluderas följande processer: Frost vittring Tillväxt av salt-kristaller Avlastning Klyvning genom växt roter

Frost vittring “A cold climate weathering process Water penetrates the joints in rock, the water freezes, expands, the expansion produces outward pressure on the joint and the joint or crack enlarges”. Hallet, 2006: Science, 314, 1092-1093 Landformer: rock glaciers, talus kon

Bergrund Disintegrering Bergrund bryts genom bestående sprickor. Vittring processer använda sprickor. Block separation Rock breaks along joints and bedding planes. Grusvittring weathering processes separate the individual grains of a coarse grained rock

Tillväxt av saltkristaller Vittring process i torra och kustområden Fukt migrerar till markytan genom kappilärt stigning av grundvatten Vatten avdunstas och mineraler stannar kvar Saltkristall växt leder till grusvittring Effektivt i sandsten (poröst material)

Avlastning/exfoliation Expansion av yttra berggrundslager vid erosion av överliggande berggrund. Nedbrytning parallellt med jordytan i stora lager

Fler mekaniska vittringsprocesser Expansion och krympning av material genom temperaturförändringar. Växtrötter som tränger ner i sprickor i berggrund.

Kemiska Vittring Nedbrytning och and förfall av mineraler i material genom kemiska förändring Oxidation, hydrolys och genom karbonisk syre Takten av kemiska vittring ökar med temperatur och fuktighet. Producerar ett rundade landskap FEL

Hydrolys och Oxidation Bergarts mineraler reagera med vatten för att producera nya mineraler. Producerar mjuk, lera-artig material som lätt eroderas. I torra klimaten kan hydrolys resulteras i grusvittring

Vittring genom syror Syra bildas av vatten och svavel, koldioxid och kvävedioxid. Vatten och CO2 formar karbonisk syra som är mycket effektivt att lösa up kalksten Karst landformer Surt nederbörd

Mass rörelse Rörelse av regolit och berggrund genom direkt påverkan av gravitation.

Mass rörelse processer – ett alternativt klassifikation

Mass rörelse mekanismer Flöde (viscous behaviour) Skred (plastic behaviour) Hävning

Creep/Krypning (Kanada)

Mark flöde i permafrost (Tibetansk platå)

Talus with dry grain flows (Frankrike)

Rock slope failure i kalksten (Alaska)

Slump (rotational slide) / Jordskred (Kalifornien)

Slump (rotational slide) /jordskred (Kalifornien)

Slump (rotational slide)

Mud flow / slammflöde (Kanada)

Debris flow / slammföde (Frankrike)

Lahar (Indonesien)

Sluttningar Land surfaces that are inclined from the horizontal. Mantled with regolith which is the source of sediment and soils. Guide the downhill flow of water and sediment

Jord Krypning

Jordskred/ slammflöde

Slamflöde Flowing mud of varying consistency concrete to very fluid Very fluid mudflows are called debris flows Common in desert areas.

Landslides Sliding of large masses of rock Associated with steep slopes, earthquakes, mining.

Human Induced Mass Wasting Piling waste into unstable accumulations Removal of support by undermining Scarification Excavations and other disturbances for mining Open pit and strip mines, gravel pits

Arctic and Alpine Tundra Periglacial regions and landforms Formed near ice and in cold areas. Develop distinctive landforms of weathering and mass wasting due to the extreme cold. Large annual temperature range = freezing and thawing.

Permafrost Perennially frozen ground and bedrock (<0°C). Found in tundra and boreal forest climates Depth Approximately 300 m thick – North America 300 – 1000 m thick in Siberia Much current permafrost is a remnant of the last ice age.

Types of Permafrost Continuous permafrost Discontinuous permafrost Extends without gaps under all surface features Coincides with tundra climate Discontinuous permafrost Occurs in patches, frost free zones under rivers and lakes. Coincides with the boreal forest climate Sporadic permafrost Occasional patches of permafrost exist. Subsea permafrost Below sea level in the shallow offshore zone Alpine permafrost Found at high elevations where average annual temperature is below freezing

Distribution of Permafrost Continuous Discontinuous Alpine Sub-sea

Permafrost Map Cross Sections

Permafrost Active Layer Talik The surface layer that thaws seasonally, each summer. Ranges in depth from 15 cm to 4 m. Thickest in subarctic areas, becoming shallower towards the poles. Talik Unfrozen areas. Often under lakes.

Energy Flows in Permafrost

Processes Frost action Mass movement Wedging, heaving, thrusting, cracking Mass movement Transports the loosened debris Facilitated by severe frost action Lack of water drainage

Forms of Ground Ice Ice Wedges Form in silty aluvium – deltas and floodplains Originate in cracks that form when permafrost shrinks during the cold. Form over hundreds of years, cracking and filling with ice year after year.

Ground Ice Ice wedge polygons Pingos Intersecting ice wedges Large, ice cored, domelike features Form from ice accumulating and forcing up the overlying sediments 50 m high and 600 m in diameter. Thousands in the Mackenzie Delta

Patterned Ground Ice-wedged Polygons Stone polygons or rings Stripes Flat surfaces Cracking creates straight sides of coarse stones with interiors of fine material. Stone polygons or rings Stone rimmed, circular forms, ranging from a few centimeters to several meters in diameter. No cracking, freezing and thawing causes horizontal movement of pebbles and cobbles. Stripes Linear arrangements – circles and polygons influenced by gravity

Patterned Ground Stone rings and stone stripes

Solifluction Large tongue-like masses of surface debris Due to thawing of the active layer Moves 1 – 3 cm. / yr. A scarp of 1 to 6 meters at the leading edge.

Alpine Tundra Periglacial processes are found at high elevations where mean annual temperature is below freezing. The elevation of continuous permafrost decreases with latitude.

Environmental Problems Occur when insulating surface layers are disturbed. Thermal Erosion As a result, the active layer deepens, ice masses melt and the ground subsides. Thermokarst Subsidence and depressions Thermokarst and streamflow in winter create engineering challenges in periglacial environments.