HIMALAYAS · ANDES
VOSGES · SATPURA
FUJI · KILIMANJARO
Mountains
Fold, Block, Volcanic & Residual Mountains · Orogenic Processes · 4 Orogenic Epochs & Global Cordilleras (28 Micro-Realms)
Orogenesis, Structural Mountain Types & Planetary Cordilleran Belts
Mountains are second-order relief features rising conspicuously (typically $>600\text{ m}$) with steep slopes, narrow summits, and deep crustal roots. Driven by tectonic plate convergence, faulting, magmatism, and differential erosion, mountains classify into four genetic types: 1) Fold Mountains (compressional buckling of geosynclinal sediments—the world's highest and most extensive), 2) Block Mountains (fault-bounded uplifted Horsts flanking Graben rifts), 3) Volcanic Mountains (cones of magma accumulation), and 4) Residual / Relict Mountains (carved by circum-denudation)—concentrated globally across the Circum-Pacific and Alpine-Himalayan belts.
I. Orogenic Processes & Fold Mountains (Compressional Tectonics)
Mountain vs. Hill Threshold
- Local relief >600 m (2,000 ft) above base
- Steep slopes ($>25^\circ$) + narrow summit crest
- Covers ~24–27% of Earth's land surface
Orogeny vs. Epeirogeny
HORIZONTAL ⇉⇇
VERTICAL ↑↓
- Orogeny (G.K. Gilbert): Mountain-building
- Tangential horizontal compression & folding
- Epeirogeny: Broad continental uplift/warp
Geosynclinal Cradle (Tethys)
- Hall-Dana-Kober Geosynclinal Theory
- Long, narrow, subsiding marine trough
- Tethys Sea sediments squeezed into Himalayas!
Andean vs. Himalayan Collision
ANDEAN ARC
HIMALAYAN
- Cordilleran (O–C): Subduction + volcanic arc (Andes, Rockies)
- Collisional (C–C): Double crust thickness (Himalayas, Alps)
1. Fold Mountains (Anticlines)
- #1 most widespread & loftiest mountain type
- Wave-like Anticlines (crests) & Synclines (troughs)
- Rich in marine fossils on high peaks!
Recumbent Folds & Nappes
- Intense compression overturns fold limbs
- Shears along low-angle thrust faults
- Displaced rock sheet = Nappe (Kashmir/Simla)
Isostatic Crustal Roots
- Airy Isostasy: Mountains float on mantle
- Supported by deep buoyant SIAL root (70 km)
- Erosion of peak triggers isostatic rebound
II. Block (Horst), Volcanic (Accumulation), Dome & Residual Mountains
2. Block Mountains (Faulted)
- Formed by tensile stretching or compression
- Crust fractures along steep fault planes
- Flat tops + steep linear fault scarps
Horst (Pillar) & Graben (Rift)
- Horst: Up-thrown or standing central block
- Graben: Down-dropped rift valley trough
- Created by either block uplift OR side sinking
Tilted vs. Lifted Block Mtns
- Lifted: Two boundary faults; flat summit
- Tilted: Rotated on one fault; gentle backslope
- Basin and Range Province (Western USA)
Global Block Mountain Key
- Vosges (France) & Black Forest (Germany)
- Harz Mtns, Sierra Nevada (world's largest block)
- Salt Range (Pakistan) & Rwenzori (Africa)
3. Volcanic Mountains
- Also called "Mountains of Accumulation"
- Built by lava, ash, cinders & pyroclasts
- Fuji, Kilimanjaro, Cotopaxi, Mauna Loa, Barren Isl.
Dome / Laccolith Mountains
- Magma intrudes without breaching surface
- Blisters overlying strata into a circular dome
- Black Hills (S. Dakota) & Henry Mtns (Utah)
4. Residual / Relict Mountains
- "Mountains of Circum-Denudation"
- Hard resistant core left after agents erode
- Ancient fold/plateau (Aravalli, Nilgiri, Parasnath)
III. The Four Orogenic Epochs & Global Mountain Distribution Systems
Cordilleran Spatial Hierarchy
- Range: Single coeval line of peaks (Himadri)
- System: Parallel ranges of same age
- Cordillera: Multi-age continental super-belt
1. Pre-Cambrian Orogeny
- Oldest mountain-building epoch (>540 Ma)
- Heavily peneplained & metamorphosed roots
- Aravallis (India), Laurentian (Canada), Fenno-Scandia
2. Caledonian Orogeny
- Named after Caledonia (ancient Scotland)
- Closure of proto-Atlantic Iapetus Ocean
- Scottish Highlands, Scandinavian Mtns, N. Appalachians
3. Hercynian (Variscan)
- Pangea assembly collision (Laurasia + Gondwana)
- Urals, Pennines, Vosges, Black Forest,
- Appalachians, Altai & Tien Shan
4. Alpine-Himalayan Orogeny
- Youngest, ruggedest & highest fold mountains
- Still tectonically active & rising today
- Himalayas, Alps, Andes, Rockies, Atlas
Circum-Pacific Cordilleras
RING
- Andes (7,000 km — longest continental range!)
- North American Cordillera (Rockies, Cascades, Alaska)
- Kamchatka, Japan, Philippines, NZ Southern Alps
Alpine-Himalayan & Pamir Knot
- West-to-East Tethyan collision belt
- Pyrenees, Alps, Carpathians, Caucasus, Zagros
- Pamir Knot radiates Hindu Kush, Kunlun, Karakoram, Himalayas
IV. Mid-Oceanic Ridge & Indian Mountain Architecture (Prelims Synthesis)
Mid-Oceanic Ridge (65,000 km)
- Longest mountain chain on Planet Earth!
- 65,000-km submarine basaltic spreading ridge
- Rises 2–3 km above abyssal floor (Iceland exposed)
Aravalli Range (Oldest Relict)
- Originally a lofty Pre-Cambrian Fold mountain
- Now a worn-down Relict / Residual range
- 800 km from Gujarat to Delhi Ridge
Vindhya & Satpura Horsts
- Satpura is a classic Horst Block Mountain!
- Flanked by Narmada Graben (N) & Tapi Graben (S)
- Highest peak: Dhupgarh (1,350 m on Mahadeo)
Western vs. Eastern Ghats
FAULT SCARP
RELICT FOLD
- Western Ghats (Sahyadri): Continuous faulted plateau escarpment (Anamudi 2,695 m)
- Eastern Ghats: Ancient Pre-Cambrian relict fold belt dissected by rivers (Jindhagada)
Himalayan Syntaxial Bends
- 2,400-km convex-southward young fold arc
- Knee-bend hairpins at Nanga Parbat (W)
- And Namcha Barwa (E) around Peninsular horns
Water Towers & Altitudinal Belts
- Tropical $\to$ Temperate $\to$ Alpine $\to$ Nival snowline
- Orographic barrier forces monsoon rainfall
- Cryospheric "Water Towers" feeding perennial rivers
Master Mountains Matrix
- 4 Genetic Types + 4 Orogenic Epochs
- 2 Global Continental Belts + 1 Submarine MOR
- Transitions to Realm 60 (Plateaus & Plains)
Core Distinctions
• Fold Mountains (Compressional): Himalayas, Alps, Andes, Rockies, Atlas, Urals, Appalachians, Aravallis (originally fold, now relict).
• Block Mountains (Fault-Bounded Horst): Vosges (France), Black Forest (Germany), Harz, Sierra Nevada (USA), Salt Range (Pakistan), Satpura & Vindhya (India).
• Volcanic Mountains (Accumulation): Mt. Fuji, Kilimanjaro, Cotopaxi, Chimborazo, Mauna Loa, Vesuvius, Barren Island.
• Residual / Relict Mountains (Circum-Denudation): Aravallis, Nilgiris, Parasnath, Rajmahal, Eastern Ghats.
1) Pre-Cambrian (>540 Ma): Aravalli, Laurentian, Algoman.
2) Caledonian (~430–380 Ma · Silurian-Devonian): Scottish Highlands, Scandinavian Mountains.
3) Hercynian / Variscan (~340–250 Ma · Carboniferous-Permian): Urals, Appalachians, Vosges, Black Forest, Tien Shan.
4) Alpine-Himalayan (65 Ma–Present · Tertiary): Himalayas, Alps, Andes, Rockies, Atlas.
The Western Ghats (Sahyadris) are NOT true fold mountains; they are the faulted, uplifted western escarpment edge of the Deccan Peninsular plateau formed when India rifted from Madagascar. The Satpuras are a classic Horst Block Mountain between the Narmada and Tapi grabens, while the Aravallis are a Pre-Cambrian Relict Fold Mountain.
Global Mountains Matrix
Genesis, Orogenic Epoch & Exemplars