2 Glaciera thick ice mass that originates on land from the accumulation, compaction, and recrystallization of snow.Agents of erosion – acquire, transport and deposit sedimentOccupy ~10% of land area“Interrupts” hydrologic cycle by “locking up” water
3 Glacier Types 1. Valley (Alpine) Found in mountainous areas Smaller than ice sheetsLengths greater than widthsOnly cover a small regionTransform V-shaped valleys into U -shaped valleys
7 Daily Questions Upslope The images were taken at the same location but with 59 years between the photos.Which direction is the ice moving (upslope or downslope)?Which direction is the glacier moving (upslope or downslope)?Is there a difference between the directions – explain.DownslopeUpslopeDownslopeFig. 16.3
8 Glacier movement Gravity primary force Entire ice sheet moves 5 to 50 m/yrPlastic flow – flowing solidBasal slip – movement over bedrockFastest movement within the centerFriction Slows down the sides
11 Glacier Budget In - Zone of accumulation Out – Zone of wastage Snow accumulates and forms iceOuter limit is the snowlineOut – Zone of wastageablation – general term for loss of ice or snow from a glacierSublimationMeltingEvaporationCalving - icebergs
12 Glacier budgetZone of AccumulationZone of WastageIf ice formation is greater than ice loss – glacier advances downslopeIf ice formation is less than ice loss – glacier retreats upslopeIf ice formation is = ice loss – glacier position is stationary
14 Glacier Erosion and Deposition Plucking – loosen and lift blocks of rock (mechanical weathering)Abrasion – sediment in ice acts as giant “sandpaper”Creates Rock flour – very fine-grained materialCreates Striations – grooves scratched in bedrock that indicate direction of ice movement
27 Causes of Glaciation Full Reasoning is not known Theory of Glaciation needs to include:Interglacial periods – periods of warm climate separating periods of glacial advancements.Glacial episodes in the Paleozoic ( mya) and Precambrian time (700 mya).
29 Causes of Glaciation Full Reasoning is not known Theory of Glaciation needs to include:Interglacial periods – periods of warm climate separating periods of glacial advancements.Glacial episodes in the Paleozoic ( mya) and Precambrian time (700 mya).Earth’s average global is 14oC, in the geologic past it was 22oC – Glaciation requires a temp. of about 10oC.Continental glaciers originate in polar or elevated land.Sufficient precipitation needs to occur.
30 Milankovitch cycles Earth’s orbital changes controls its climate EccentricityMeasure of the nooncircularity of Earth's orbitCycle is about 100,000 years
32 Milankovitch cycles Eccentricity Inclination The changes in the axial tilt (22o to 24.5o) of the EarthThe greater the tilt the greater the contrast between summer and winter temperaturesCycle is about 41,000 years
36 Milankovitch cyclesMain effect of cycles is to change the contrast in the temperature of the summer and winter.Glaciation would occur when the summer temperature is closer to the winter temperature, but winter temperature are not colder than usual.Rather the mild summers melt less ice than is received in the winter.