Transcript Document
Glaciers Glacier • a thick ice mass that originates on land from the accumulation, compaction, and recrystallization of snow. • Agents of erosion – acquire, transport and deposit sediment • Occupy ~10% of land area • “Interrupts” hydrologic cycle by “locking up” water Glacier Types 1. Valley (Alpine) • Found in mountainous areas • Smaller than ice sheets • Lengths greater than widths • Only cover a small region • Transform V-shaped valleys into U -shaped valleys Alpine Glaciers Glacier Types 2. Ice sheets (Continental glacier) • Large scale – cover 10% of Earth’s land • Found in polar regions – Greenland – 1.7 million km2 – Antarctica – 13.9 million km2 Continental Glaciers Daily Questions Upslope The images were taken at the same location but with 59 years between the photos. 1) Which direction is the ice moving (upslope or downslope)? 2) Which direction is the glacier moving (upslope or downslope)? 3) Is there a difference between the directions – explain. Fig. 16.3 Glacier movement •Gravity primary force •Entire ice sheet moves 5 to 50 m/yr – Plastic flow – flowing solid – Basal slip – movement over bedrock •Fastest movement within the center •Friction Slows down the sides Glacier movement 20 meters 100 meters Glacier movement Glacier Budget In - Zone of accumulation Snow accumulates and forms ice Outer limit is the snowline Out – Zone of wastage ablation – general term for loss of ice or snow from a glacier 1. Sublimation 2. Melting 3. Evaporation 4. Calving - icebergs Glacier budget Zone of Accumulation Zone of Wastage • If ice formation is greater than ice loss – glacier advances downslope • If ice formation is less than ice loss – glacier retreats upslope • If ice formation is = ice loss – glacier position is stationary 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 material Creates Striations – grooves scratched in bedrock that indicate direction of ice movement 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. 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 (200-300 mya) and Precambrian time (700 mya). 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 (200-300 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. Milankovitch cycles • Earth’s orbital changes controls its climate • Eccentricity – Measure of the nooncircularity of Earth's orbit – Cycle is about 100,000 years Milankovitch cycles • Eccentricity • Inclination – The changes in the axial tilt (22o to 24.5o) of the Earth – The greater the tilt the greater the contrast between summer and winter temperatures – Cycle is about 41,000 years Milankovitch cycles • Eccentricity • Inclination • Precession – The wobble of the Earth as it spins on its axis – Cycle is about 26,000 years Milankovitch cycles • Main 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.