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 Formation of glacial ice from snow Snow Firn Ice 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 noncircularity 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. 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 Glacier movement •Gravity primary force •Entire ice sheet moves – Plastic flow – flowing solid 100’s m/yr – Basal slip – movement over bedrock 100’s m/yr •Fastest movement within the center •Friction Slows down the sides Glacier movement 20 meters 100 meters Glacier movement Mechanisms of Glacial Movement • Rotation of Grains • Melting and Freezing • Internal Slipping Rotation of Grains Melting & Freezing Internal Slipping 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. Evaporation 3. Melting 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 Glacial Moraines • Layers or ridges of glacial till that has been transported and deposited by a glacier • Lateral Moraines – Associated with alpine glaciers – Material that accumulates between the ice and the valley walls • Medial Moraines – Associated with alpine glaciers – Form when two glaciers merge – lateral moraines combine into one End Moraines Debris pushed along in front of the glacier 1. Terminal End Moraine – marks the furthest extent of the glacier advancement 2. Recessional End Moraine – formed as the front periodically became stationary during the glacial retreat Ground Moraine debris accumulated and deposited under the glacier