Chapter 15

Glaciers and Glaciation Glaciers seasonal) mass of ice that is formed on land and moves under the force of gravity. accumulation exceed seasonal melt. • is a large, permanent (non- A glacier • Glaciers may form anywhere that snow ) may cover ice sheets ( is one that occupies a valley, form in the mountains. is a mass of ice that occupies high ice cap valley glacier Types of Glaciers mountain area and flows outward in several mountain area and flows outward directions. –A –A –An –An large sections of continents as in Greenland and Antarctica. Alpine glaciers Continental glaciers • • ). zone zone ; the region below is the line below which melting, sublimation, calving ( snow line head and lose to melt at its foot. of accumulation annual snow cover is lost in summer. will advance. of wastage Glacier Dynamics • A typical valley glacier will add snow at its •The • region above the snowline is The • If it gains more than loses, its terminus • If it loses more than gains, will retreat. Glacier Dynamics . (It floats.) 3

Properties of Ice vertical cliff higher than 40m (130ft). • Ice has a density of 0.96 g/cm • Ice is a weak solid and will not hold • Ice will flow under it own weight. • can cause local melting. Pressure Crevasses, Seracs, and Ogives •A crevasse is a fracture in the glacier surface. – Crevasses form where the surface is in tension. – Crevasses are rarely more than about 40 m deep. –A bergschrund is a crevasse at the head of a glacier. •A serac is a large, irregular block of ice formed by intersecting crevasses •An ogive is compressional wave in the glacier surface. ) left by a glacier. till are left at the ends. are left at the sides of glaciers are left in the centers. is a deposit of unsorted (silt- to Moraines Lateral moraines Medial moraines Terminal moraines moraine – – – boulder-size) material ( •A •A Landforms is a rounded, striated outcrop hill. is a low, sinuous hill of till left by is a depression in an outwash plain

Continental Glacial esker drumlin kettle left by a buried block of ice that has melted. sub-glacial stream. •An •An •A •A •A . U-shape is the valley of a tributary is a steep-walled bowl-shaped valley at is a narrow ridge between two cirques. is a peak at the intersection of arêtes. is a glacial valley that opens to the sea. arête cirque hanging valley horn fjord the head of a glacier. the head of glacier. • Glacial valleys have a characteristic •An •An •A •A Mountain Glacial Landforms •A •A •A Glacial Valleys Hanging Mountain

Landforms: U-shaped & ) are the Ice Ages. Ice Ages Pleistocene ( peaked about 18,000 years ago. sheets melted away less than 7000 years ago. • last 1.8 million years of geologic time The • last major ice advance in North America The • at 14,500 years ago. abruptly warmed Climate • abruptly (~6ºC) It cooled again and then warmed • at about 11,500 to near current levels. • last remnants of the North American Ice The Previous Ice Ages • (300 million years) Permian • Neo-Proterozoic (570 million years) • boundary? Archaean-Proterozoic Namibia Striations

Glaciation in Glaciation Previous Ice Ages from Permian variation. 2 • Eccentricity of orbit (100,000 y cycle). • Tilt of rotation axis (41,000 y cycle). • of rotation axis (23,000 y cycle). Precession •CO • Continental drift and polar continents.

Causes of Ice Ages

Eccentricity Tilt Precession Continental Drift Variation

2

CO variation correlates with global 2 – It transmits visible and UV radiation – IR radiation. It blocks temperature. • Carbon dioxide is a greenhouse gas. •CO

–Terminal – Lateral –Medial Valley • Drumlin •Esker • Kettle • Hanging • Moraine •Snow Line •Snow • Sublimation • Calving • Crevasse • Bergschrund • Serac • Ogive •Till

Glacial Terms • Glacier Cap • Alpine Glacier Sheet •Ice •Ice •Horn •Arête • Cirque •Fjord