CORRIE TARN LAKE
SAW-TOOTHED ARÊTE
TRUNCATED SPURS
Glacial Erosional Landforms
Cirques & Tarn Lakes · Arêtes, Serrated Ridges & Horns · U-Shaped Troughs, Hanging Valleys & Fjords (28 Micro-Realms)
From Armchair Cirque Hollows to Drowned Fjord Coasts (NCERT Chapter 7)
Cirques are the most common of landforms in glaciated mountains—deep, long, and wide armchair-like basins with steep concave walls that hold Cirque or Tarn Lakes after the ice melts. When two or more cirques cut back headward into a ridge, the divide narrows into a saw-toothed, knife-edged Arête (Serrated Ridge), while three or more radiating cirques sculpt a sharp pyramidal Horn (such as the Matterhorn in the Alps and Mt. Everest in the Himalayas). Downvalley, glaciers carve broad U-Shaped Glacial Troughs flanked by Truncated Spurs, Hanging Valleys, and coastal seawater-filled Fjords.
I. Cirques (Corries) & Tarn Lakes (NCERT Core)
Cirques (Most Common — NCERT)
- Most common landform in glaciated mountains
- Found at the heads of glacial valleys
- Deep, long & wide troughs or basins
Armchair Cirque Anatomy
- 1) Very steep concave to vertically dropping
- High walls at its head as well as sides
- 2) Overdeepened bowl + 3) Raised rock lip
Rotational Slip & Plucking
- Accumulated snow turns to ice at valley head
- Rotational slip scoops deep rock basin
- Bergschrund freeze-thaw plucks headwall
Nivation Hollow Cradle
- Embryonic stage before a true cirque
- Perennial snowpatch freeze-thaw + melt wash
- Excavates shallow hillside depression
Corrie, Cwm, Kar & Botn
- Cirque (French) = Corrie (Scotland)
- Cwm (Wales — Western Cwm on Everest!)
- Kar (Germany/Austria) & Botn (Scandinavia)
Cirque or Tarn Lakes (NCERT)
- Lake of water seen quite often within cirque
- After the glacier disappears / melts
- Called Cirque or Tarn Lakes (NCERT)
Stepped / Compound Cirques
- Two or more cirques may feed into
- One another in a stepped sequence
- Each holding a stepped tarn lake (NCERT)
II. Arêtes, Serrated Ridges, Cols & Pyramidal Horns (NCERT Core)
Arêtes & Serrated Ridges
- Very narrow, sharp crest with steep sides
- Zig-zag outline + saw-toothed profile
- Cannot be climbed easily (NCERT)
Two-Cirque Divide Narrowing
- Two adjacent cirques erode back-to-back
- Headward plucking eats away the divide
- Leaves knife-edged rock spine (Arête)
Cols (Glacial Mountain Passes)
- Two opposing cirques breach the arête wall
- Creates a low U-shaped saddle notch
- Called a Col (Indira Col / South Col)
Horns (Pyramidal Peaks)
- Form through headward erosion of
- THREE OR MORE radiating cirques (NCERT)
- Meet to form high, sharp-pointed peak
Matterhorn & Mt. Everest
- Highest peak in Alps = Matterhorn
- Highest peak in Himalayas = Everest
- Both are Horns formed by cirque erosion!
Nunataks ("Ice Islands")
- Inuit term for isolated mountain peak
- Projecting above a continental ice sheet
- Shaped by frost-wedging above ice
Comb Ridges & Gendarmes
- Frost-wedging along vertical arête joints
- Carves jagged rock towers (Gendarmes)
- Resembles teeth of a comb
III. Glacial Troughs, Hanging Valleys, Truncated Spurs & Paternoster Lakes
U-Shaped Glacial Troughs
- Glaciated valleys are trough-like & U-shaped
- Broad floors + relatively smooth,
- Steep sides (NCERT Chapter 7)
V-Valley vs. U-Trough
- River erodes narrow channel bed $\to$ V-shape
- Glacier fills entire valley width & scours walls
- Straightens & widens V into parabolic U
Hanging Valleys (NCERT)
- Main glacier erodes much deeper than tributary
- Tributary valleys hang at higher elevation
- Plunge into main trough as waterfalls!
Truncated Spurs (NCERT)
- Rigid ice cannot bend around river spurs
- Bulldozes & shears off interlocking spurs
- Leaves triangular facets on trough walls
Paternoster Lakes
- Chain of lakes scooped in glacial steps
- Connected by a single stream or braided channel
- Resembles beads on a rosary string!
Ribbon (Finger) Lakes
- Long, narrow, deep lake on trough floor
- Scooped out of soft fault zone or dammed
- Loch Ness (Scotland) & NY Finger Lakes
Glacial Steps & Riegels
- Longitudinal profile of glacial trough is stepped
- Alternating hard rock bars (Riegels)
- And overdeepened plucked rock basins
IV. Fjords (Drowned Troughs), Ice-Scoured Shields & Himalayan Exemplars
Fjords / Fiords (NCERT)
- Very deep glacial troughs filled with
- Sea water & making up high-latitude
- Shorelines are called Fjords/Fiords!
Fjord Threshold Sill
- Thick inland ice scours 1,000+ m below sea
- Thinner snout at coast leaves shallow sill
- Distinguishes Fjords from fluvial Rias!
Global Fjord Belts
- Sognefjord (Norway — 205 km long, 1,308 m deep)
- Milford Sound (NZ), Patagonia (Chile),
- British Columbia / Alaska & Greenland
Whalebacks & Rock Drumlins
- Symmetrical streamlined bedrock bosses
- Polished smooth on both stoss & lee sides
- Lack the plucked lee cliff of Roche Moutonnée
Knock-and-Lochan Shields
- Continental ice sheet scours ancient craton
- Rounded gneiss knobs (Knocks) +
- Thousands of rock-basin lakes (Finland/Canada)
Indian Himalayan Horns & Cols
KAILASH · INDIRA COL
- Horns: Mt. Shivling ("Matterhorn of India"), Nanda Devi, Ama Dablam
- Cols: Indira Col (Siachen — India's northernmost point!)
Indian Tarn Lakes & Valleys
- Tarn Lakes: Roopkund, Hemkund Sahib, Satopanth, Chandratal, Suraj Tal
- U-Troughs & Hanging Valleys: Har-ki-Dun & Valley of Flowers
Core Distinctions
• 1 Cirque: Deep armchair-like basin at the head of a glacial valley; holds a Tarn Lake after the ice melts.
• 2 Opposing Cirques: Headward erosion from two sides narrows the divide into a saw-toothed, knife-edged Arête (Serrated Ridge); if breached, it forms a Col.
• 3 or More Radiating Cirques: Headward erosion of three or more cirques cuts a high, sharp-pointed, steep-sided pyramidal peak called a Horn (e.g., The Matterhorn in the Alps and Mt. Everest in the Himalayas — NCERT).
Because the main trunk glacier is much thicker and heavier than its tributaries, it erodes its U-shaped trough floor far deeper—leaving tributary valleys hanging high on either side as waterfall ledges, while shearing off interlocking river spurs into triangular Truncated Spurs.
3. Fjord (Glacial Trough) vs. Ria (Fluvial Valley)A Fjord is a submerged U-shaped glacial trough in high latitudes with vertical walls and a shallow threshold sill at its mouth. A Ria is a submerged V-shaped river valley that deepens continuously towards the open sea.
Glacial Erosional Matrix
NCERT Chapter 7 & Himalayan Exemplars