Geomorfologi I Vittring och massrrelse Vittring Alla processer

Geomorfologi I: Vittring och massrörelse

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

Vittring • Fysiskt/mekaniskt 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 CO 2 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 – 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 – 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 – 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 – Intersecting ice wedges • Pingos – 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 – 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.