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
1. SNOWFLAKES ACCUMULATE
2. SNOWFLAKES COMPACT
3. FIRST INTO FIRN (LIKE PACKED
SNOWBALLS)
4. 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:
A. Abrasion – wearing, grinding, scraping
rock surface because rock fragments are
frozen into the ice at the bottom (ROCK
FLOUR)
B. 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
Materialsall 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 scouringoften 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
U-SHAPED
VALLEY
CIRQUE
HANGING
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
f05_07a_pg84
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
Esker
Till
Moraine-dammed
lake
Terminal Moraine
Glacial
Stream
DRUMLIN
DRUMLINS