🌍 Class 11 Geography – Chapter 7
Landforms and Their Development
✨ Geo-shapes (भू-आकृतियाँ)
- The factors of erosion (अपक्षय) play a major role in shaping the earth’s surface.
- Important agents: Rivers, Winds, Glaciers, and Waves.
- These agents break the rocks, carry sediments (गाद) and deposit them elsewhere.
- As a result, two main types of landforms are created:
- Erosional Landforms (क्षरणात्मक आकृतियाँ)
- Depositional Landforms (निक्षेपात्मक आकृतियाँ)
📖 Geomorphology (भू-आकृति विज्ञान)
- The scientific study of the history of the Earth’s surface.
- It includes:
- Surface shapes (आकृति)
- Materials (पदार्थ)
- Processes (प्रक्रियाएँ) which form the land surface.
🏞️ Major Landforms
- Volcano 🌋 (ज्वालामुखी)
- Canyon 🏜️ (गहरी घाटी)
- Mountain ⛰️ (पर्वत)
- Plain 🌾 (मैदानी क्षेत्र)
- Island 🏝️ (द्वीप)
- Lake 🏞️ (झील)
- Waterfall 💧 (जलप्रपात)
- Valley 🌄 (घाटी)
⛏️ Erosional Landforms (क्षरणात्मक आकृतियाँ)
Formed by rivers:
- V-shaped valley (V आकार की घाटी)
- Gorge (संकरी गहरी घाटी)
- Canyon (कैन्यन)
- Waterfall (जलप्रपात)
- Eroded fissures (दरारें)
🏗️ Depositional Landforms (निक्षेपात्मक आकृतियाँ)
Formed by deposition of sediments:
- River terraces (नदी वेदिका)
- Oxbow lake (गोखुर झील)
- Braided river (गुंफित नदी)
🌊 River / Flowing Water (नदी / प्रवाहित जल)
The river creates different landforms in three stages of its life cycle:
1️⃣ Youth Stage (युवा अवस्था – पर्वतीय क्षेत्र)
- Found in mountainous regions.
- Few rivers in number.
- Forms V-shaped valleys.
- Flood plains are absent or very narrow.
- Presence of swamps and lakes in wide divides.
2️⃣ Mature Stage (प्रौढ़ अवस्था – मैदानी क्षेत्र)
- Found in plains.
- Large amount of water with many tributaries (सहायक नदियाँ).
- Valleys are still V-shaped but much deeper.
- Broad flood plains develop.
- The river starts forming meanders (घुमावदार मोड़).
3️⃣ Old Age Stage (प्रौढ़ावस्था – डेल्टा क्षेत्र)
- Found in delta regions.
- Tributaries become fewer.
- River slope becomes gentle (धीमा ढलान).
- Flows freely in wide flood plains.
- Creates river estuaries (मुहाना), natural levees (प्राकृतिक तटबंध), oxbow lakes etc.
🌍 Erosional Landforms (क्षरणात्मक आकृतियाँ)
🌄 Valleys (घाटियाँ)
- Valleys begin with small streams (छोटी नदियाँ).
- These streams gradually become wider, deeper, and longer → finally form valleys.
- Valleys are classified based on length, width, and shape:
- V-shaped Valley (V आकार की घाटी)
- Gorge (संकरी गहरी घाटी)
- Canyon (कैन्यन)
🏞️ Gorge (संकरी घाटी)
- A deep, narrow valley with steep slopes on both sides.
- Width of gorge is almost same at top and bottom.
- Commonly formed in hard rock regions.
🏜️ Canyon (कैन्यन)
- Has steep slopes like a gorge but:
- Wider at the top than the bottom.
- Usually formed by horizontal stratification (परतदार संरचना) of sedimentary rocks.
💧 Pot Hole / Water Socket (जल गड्ढा)
- When rock pieces get stuck in river bed and rotate continuously → form a circular trough (गर्त).
- This is called a Pot Hole.
🌀 Plunge Pool (गर्तकूप)
- A deep & large depression (गहरा गड्ढा) formed at the base of a waterfall.
- Created by:
- Falling water pressure
- Circular rotation of boulders (बड़े पत्थर)
- Helps in deepening valleys.
🪨 River Terraces (नदी वेदिका)
- Step-like landforms on the sides of a river valley.
- Represent remnants of old flood plains.
- Formed due to vertical erosion of flood plains.
- Can occur at different heights, showing past river levels.
🔹 Types of River Terraces
- Paired Terraces (युग्म वेदिका) –
- Found at equal height on both river banks.
- Unpaired Terraces (अयुग्म वेदिका) –
- Present only on one side OR at different heights.
🔹 Causes of River Terrace Formation
- Decrease in river water flow.
- Climate change → change in river area.
- Tectonic activity (भूकंपीय कारण).
- Change in sea level (for rivers near coasts).
🌊 Waterfall (जलप्रपात)
- When a river flows over hard rock (कटाव-रोधी चट्टान) followed by soft rock (आसानी से कटने वाली चट्टान):
- Soft rock erodes faster → river bed develops a sudden drop → forms a waterfall.
⛲ Cascade / Kshiprika (क्षिप्रिका)
- When hard and soft rocks occur alternately in the river bed:
- River forms a step-like pattern.
- Creates several small waterfalls → called Kshiprikas / Cascades.
Landforms and Their Evolution (Notes in English)
✴️ Depositional Landforms
1️⃣ Alluvial Fan (जलोढ़ पंखा)
- When rivers descend from mountainous regions, their flow slows down.
- Pebbles & sediments get deposited in a fan-shaped form.
- This depositional feature is called Alluvial Fan.
2️⃣ Delta (डेल्टा)
- At the mouth of rivers (before meeting the sea), flow becomes very slow due to gentle slope (मंद ढाल).
- Sediments are deposited in a triangular shape → called Delta.
3️⃣ Flood Plains (बाढ़ मैदान)
- Just as valleys are formed by erosion, floodplains are formed by deposition.
- Fine materials like sand, clay, pebbles get deposited on river banks during annual floods.
- These flat lands are called Flood Plains.
4️⃣ Meanders / River Vispar (नदी विसर्प)
- S-shaped curves formed in the plains due to slow flow & heavy load.
- Erosion on the outer bank & deposition on the inner bank increases the curve.
- Over time, meanders get cut off → forming Ox-bow Lakes (गोहूर झील).
5️⃣ Braided River (गुंफित नदी)
- In the lower valleys, rivers deposit sediments.
- River divides into many channels separated by sand bars (रेतीली दीवारें).
- Such rivers are called Braided Rivers.
💧 Landforms by Groundwater
- Groundwater moves through joints, cracks, holes → dissolves limestone (चूना-पत्थर).
- Creates erosional & depositional landforms.
🌀 Erosional Landforms by Groundwater
- Sinkholes / Swallow Holes (गर्त/घुलनशील गर्त): Funnel-shaped depressions, depth 0.5 to 30+ meters.
- Solution Sink (विलयन गर्त): Formed at bottom of limestone rocks by dissolving action.
- Lapies (लैपिस): Sharp, irregular ridges formed when limestone dissolves along cracks.
🏛️ Depositional Landforms by Groundwater
- Stalactite (स्टैलेक्टाइट): Hanging pillar from cave roof formed by deposition of lime.
- Stalagmite (स्टैलैग्माइट): Rising pillar from cave floor due to lime deposition.
- Pillar (स्तंभ): When stalactite & stalagmite join → Lime Pillar (चूना स्तंभ).
❄️ Landforms by Glaciers
- Glacier: Slow-moving mass of ice flowing from mountains to valleys.
Types of Glaciers
- Continental Glaciers (महाद्वीपीय हिमनद): Spread over vast areas.
- Valley Glaciers (घाटी हिमनद): Flow in mountain valleys.
Features
- Flow is very slow (few cm to few meters/day).
- Moved mainly by gravity (गुरुत्वाकर्षण).
🪨 Erosional Landforms by Glaciers
- Cirque (सर्क): Bowl-shaped hollow at glacier head.
- Tarn Lake (टार्न झील): Lake formed in cirque by melting ice.
- Horn (श्रृंग): Sharp peak formed when several cirques meet.
⛰️ Depositional Landforms by Glaciers
- Drumlin (ड्रमलिन): Oval hill of sand & gravel deposited by glacier.
- Roche Moutonnée / Sheep Rock (शीप रॉक): Rock with gentle slope on one side, steep on the other.
- Fiord (फियोर्ड): Deep glacial trough filled with sea water along coast.
🏜️ Landforms by Wind (Aeolian Landforms)
- Winds act mainly in desert & semi-arid regions (मरुस्थल व अर्ध-शुष्क क्षेत्र).
- Erosion & deposition depend on wind speed & load carried.
🌬️ Erosional Landforms by Wind
- Mushroom Rock / Rock Pedestal (मशरूम चट्टान): Rock shaped like an umbrella due to wind abrasion.
🌙 Depositional Landforms by Wind
- Barchans (बारख़ान): Crescent-shaped sand dunes.
- Slope is gentle on one side, steep on the other.
- Move forward with strong winds.
🪨 Other Important Landforms
- Monadnock (मोनाडनॉक): Isolated residual hill left after erosion.
- Inselberg (इंसेलबर्ग): Steep isolated hill in deserts formed by erosion.
