GLACIERS A LARGE MASS OF ICE ON LAND THAT FLOWS UNDER THE PRESSURE OF ITS OWN WEIGHT – DOWNHILL OR OUTWARD DUE TO GRAVITY

Glaciers: 2 Types ALPINE(VALLEY) GLACIERS: long, slow-moving, streams of ice found in mountain areas (high elevation) occupying former river valleys CONTINENTAL GLACIERS (ICE SHEETS): very old (1000’s of years), thick (1000’s of meters) mass of ice covering almost an entire land mass GREENLAND: 1.7 Million SQ MI , 3 KM thick ANTARCTIC: 12.5 Million SQ MI, 5 KM thick

GLACIERS - VALLEY AND CONTINENTAL

CONTINENTAL ICE SHEETS

WHERE DO THEY FORM? AREAS OF HIGH LATITUDE OR HIGH ELEVATION WHERE THEY HAVE COLD SUMMERS PRESENTLY OCCUPY 10% OF WORLD’S TOTAL LAND AREA (COMPARED TO 32% DURING THE PLEISTOCENE EPOCH)

HOW DO THEY FORM? MORE SNOW MUST FALL THAN MELTS ZONE OF ACCUMULATION – SNOW TURNS TO ICE AT UPPER PART OF GLACIER ZONE OF MELTING (ABLATION) – LOWER PART SNOW LINE (EQUILIBRIUM LINE) LINE WHERE SNOW IS ALL YEAR LONG

Process of Glacier Formation SNOWFLAKES ACCUMULATE SNOWFLAKES COMPACT FIRST INTO FIRN (LIKE PACKED SNOWBALLS) LOWER LAYERS TURN INTO GLACIAL ICE (SOLID ICE – NO AIR) UNDER THE WEIGHT OF OVERLYING FIRN AND SNOW

Firn Firn is an intermediate stage between snow and glacial ice When more snow is accumulated than is melted, the snow clumps together and will ultimately become glacial ice

HOW DO GLACIERS MOVE? UNDER THE INFLUENCE OF GRAVITY THEIR OWN WEIGHT IS THE DRIVING FORCE UNDER PRESSURE THE DEEPER ICE BEHAVES LIKE A THICK FLUID (CALLED PLASTIC FLOW) AND FLOWS DOWNHILL OR SPREADS OUT IN ALL DIRECTIONS (when glacier is about 300 ft. thick)

GLACIER MOVEMENT GLACIER ADVANCES SNOWFALL > MELTING GLACIER RETREATS SNOWFALL < MELTING STATIONARY GLACIER SNOWFALL = MELTING DYNAMIC EQUILIBRIUM

ICE WITHIN GLACIER IS ALWAYS MOVING FORWARD EVEN IF THE GLACIER IS RETREATING OR STATIONARY MANY DEPOSITIONAL FEATURES ARE FORMED AS A RESULT

GLACIER FLOW SPEED IS LIKE A STREAM – FASTER IN THE MIDDLE / LESS FRICTION fastest movement after 1) heavy winters, 2) steep slopes, and 3) in summer WHY??? CREVASSES form along steep slopes because upper zone of glacier is rigid (rarely go deeper than 120ft. )

FASTEST

A CREVASSE- Evidence of movement

HOW DO GLACIERS ERODE? Most powerful erosional agent because of their great size and weight Glaciers erode by: Abrasion – wearing, grinding, scraping rock surface because rock fragments are frozen into the ice at the bottom (ROCK FLOUR) Plucking – rock fragments loosened, picked up and carried by glaciers

EROSIONAL FEATURES Striations - Grooves carved into the bedrock by pebbles and cobbles carried at the bottom of a glacier – can show direction of glacial movement Polished Bedrock Sediment - TILL - is angular and NOT SORTED AND NOT LAYERED

Unsorted Materials- all sizes mixed together.

Glacial Polish Smooth rock surfaces created as glaciers flow over bedrock.

Glacial Pavement….

ERRATIC – EVIDENCE OF GLACIER EROSION A boulder-sized rock dumped by a glacier. The rock is usually of a different type than the surrounding rock…

VALLEY GLACIERS

VALLEY GLACIER EROSIONAL FEATURES Mountain ranges that were scenic to begin with are now jagged, angular peaks GLACIERS MODIFY RIVER VALLEYS BY… TURNING THE V-SHAPE RIVER VALLEYS INTO U-SHAPED GLACIATED VALLEYS

EROSIONAL LANDSCAPE FEATURES OF VALLEY GLACIERS CIRQUES: semi-circular shaped bowl created as a glacier scours back toward the mountain (1st place snow and ice accumulate) ARÊTES: steep-sided, sharp-edged bedrock ridge formed by two glaciers eroding away on opposite sides of ridges HORNS: 3 or more cirques adjacent to one another TARNS: glacial lakes produced by glacial scouring- often found in cirques HANGING VALLEYS: valley eroded by a small tributary glacier; floor is at a higher elevation that valley it feeds into…

HORN HANGING VALLEY

ARÊTE CIRQUE

CIRQUE TARN

ARÊTE CIRQUE HANGING VALLEY U-SHAPED VALLEY

VALLEY GLACIER DEPOSITIONAL FEATURES MORAINES – unsorted, un-layered pile of till UNSORTED IS THE KEY WORD!!!! There are many types of moraines Lateral – till along side of glacier Medial – 2 glaciers come together and the lateral moraines join in a single ridge Terminal or End – farthest advance of glacier Recessional – glacier retreats, pauses, deposits – will be parallel to terminal moraine

Juneau, Alaska

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CONTINENTAL GLACIERS

CONTINENTAL OR ICE SHEET GLACIERS MOST FLOW OVER RELATIVELY FLAT AREAS SO LANDSCAPE FEATURES ARE LESS DRAMATIC – ROUNDED HILLS (valley glaciers sharpen and continental glaciers round) LAKES AND SWAMPS GREAT LAKES FINGER LAKES

The Finger Lakes consist of 11 long, narrow, roughly parallel lakes, oriented north-south as fingers of a pair of outstretched hands. The southern ends have high walls, cut by steep gorges.

CONTINENTAL GLACIER DEPOSITIONAL FEATURES MORAINES – glacially formed accumulation of debris DRUMLINS - ground moraine that is mounded into a stream-lined oval shape hill (inverted spoon) – steep side points in direction the glacier came from KETTLE LAKES – large, buried ice blocks melted and left depressions. Ex. Lake Ronkonkoma OUTWASH PLAIN - deposits made by streams after glaciers melt (sorted/stratified)

Kettle Lake Drumlins Outwash plain Till Glacial Stream Esker Outwash plain Till Moraine-dammed lake Glacial Stream Terminal Moraine

DRUMLIN

DRUMLINS