The black cotton soil of India has been formed due to the weathering of
Contents11
- Abrown forest soil
- Bfissure volcanic rock
- Cgranite and schist
- Dshale and limestone
Show answer
Answer: (B) fissure volcanic rock
Black cotton soil (regur soil) is formed from the weathering of basalt rock.
Basalt is a dark volcanic rock formed from the rapid cooling of lava during fissure volcanic eruptions.
The Deccan Plateau experienced massive volcanic eruptions creating the Deccan Traps — layers of basalt.
Over millions of years, this basalt weathered to form black soil found in Maharashtra, Gujarat, Madhya Pradesh, and Karnataka.
The soil's black color comes from iron and organic compounds in basalt.
Answer: (b) — fissure volcanic rock.
Black cotton soil covers about 5 lakh square kilometers across Maharashtra, Gujarat, Madhya Pradesh, and Karnataka, making it crucial for cotton cultivation in India.
The soil formed from basalt rock created during the Deccan Trap volcanic eruptions millions of years ago, when lava flows solidified into layers of dark volcanic rock.
UPSC is testing whether students can connect geological processes (volcanic activity) to soil formation, not just memorize soil types and locations.
Black Cotton Soil (Regur)
Geography black cotton soil
Black Cotton Soil (Regur): Formation, Distribution & Characteristics
Formed by weathering of basalt rock from Deccan Trap volcanism
Found in Maharashtra, Gujarat, Madhya Pradesh, Karnataka
Black color due to iron compounds and organic matter
Cotton cultivation gives it the name 'black cotton soil'
Formation Process
Black cotton soil forms through chemical weathering of basalt rock over millions of years. Basalt contains iron-rich minerals that break down into clay particles, giving the soil its distinctive dark color and heavy texture.
Key Characteristics
Property | Details | Significance |
|---|---|---|
Color | Black to dark brown | Iron compounds and organic matter |
Texture | Clay-rich, heavy | High water retention capacity |
Behavior | Swells when wet, cracks when dry | Self-plowing action |
Fertility | Rich in lime, potash, alumina | Excellent for cotton, sugarcane |
Depth | Shallow to deep (1-3 meters) | Varies with topography |
Distribution Map
Map of India showing black soil distribution across Maharashtra, Gujarat, Madhya Pradesh, Karnataka and parts of Andhra Pradesh and Tamil Nadu
Black soil covers the Deccan Plateau region — directly linked to basalt rock distribution
Parent Rock Confusion: Black soil comes from basalt (volcanic), not granite/schist (metamorphic) or shale/limestone (sedimentary)
Name Trap: Also called regur soil — both terms refer to the same soil type
Formation vs Distribution: Formed due to volcanic activity, distributed based on basalt presence
Deccan Traps & Fissure Volcanism
Geography fissure volcanic rock
Deccan Traps: Fissure Volcanism & Basalt Formation
Massive fissure volcanic eruptions occurred 65 million years ago
Created step-like basalt layers called 'traps'
Covers 5 lakh sq km across Western & Central India
Fissure Volcanism
Fissure volcanism occurs when lava erupts through long cracks in the earth's crust, not through a single volcanic cone. The lava flows cover vast areas, cooling rapidly to form basalt rock.
Formation Process
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Crustal Fissures Open**
Long cracks develop in earth's crust due to tectonic stress`"]
s2["`**Lava Eruption**
Molten lava erupts through fissures, not volcanic cones`"]
s3["`**Rapid Cooling**
Lava cools quickly on surface forming basalt rock`"]
s4["`**Layer Formation**
Multiple eruptions create step-like basalt layers (traps)`"]
s5["`**Weathering**
Over millions of years, basalt weathers into black soil`"]
s1 --> s2
s2 --> s3
s3 --> s4
s4 --> s5Basalt vs Other Rocks
Rock Type | Origin | Formation | Weathered Soil |
|---|---|---|---|
Basalt | Volcanic | Rapid cooling of lava | Black cotton soil |
Granite | Igneous | Slow cooling underground | Red soil |
Schist | Metamorphic | Heat & pressure on existing rock | Mixed soil types |
Limestone | Sedimentary | Marine organism deposits | Red & black mixed soil |
Fissure vs Cone: Deccan volcanism was fissure type (through cracks), not explosive cone volcanism
Basalt vs Granite: Both are igneous but basalt is volcanic (surface cooling), granite is plutonic (underground cooling)
Major Indian Soil Types
Geography
Major Soil Types of India: Classification by Parent Material
Alluvial soil covers 40% of India's land area
Each soil type linked to specific parent rock material
Climate and relief modify soil characteristics
Soil Types & Parent Material
Soil Type | Parent Material | Formation Process | Distribution | Key Crops |
|---|---|---|---|---|
Alluvial | River sediments | Deposition by rivers | Ganga-Brahmaputra plains | Rice, wheat, sugarcane |
Black (Regur) | Basalt rock | Volcanic weathering | Deccan Plateau | Cotton, sugarcane |
Red | Granite, gneiss | Crystalline rock weathering | Peninsular uplands | Millets, groundnut |
Laterite | Various rocks | Leaching in high rainfall | Western Ghats, Northeast | Cashew, rubber |
Desert | Sandstone | Physical weathering | Rajasthan, Gujarat | Millets, drought crops |
Mountain | Various rocks | Altitude weathering | Himalayas, Western Ghats | Tea, coffee, spices |
Soil Formation Factors
# Soil Formation
## Parent Material
- Igneous rocks
- Sedimentary rocks
- Metamorphic rocks
- Transported sediments
## Climate
- Temperature
- Rainfall
- Humidity
- Wind
## Relief
- Slope
- Altitude
- Drainage
- Aspect
## Time
- Geological age
- Weathering durationParent Material: Each soil has specific parent rock — black from basalt, red from granite, alluvial from river deposits
Distribution Pattern: Soil types follow geological formations — Deccan = basalt = black soil
Color Indicators: Soil color reveals parent material — iron content gives red/black colors