Landforms and Rocks: A Comprehensive Guide
Landforms and Rocks
1. Reasons for Landform Characteristics
(i) Young vs. Old Fold Mountains
Young fold mountains: These recently uplifted mountains are still being actively eroded, resulting in sharp peaks, deep valleys, and rugged terrain.
Old fold mountains: These mountains have undergone prolonged erosion, leading to gentler slopes and rounded summits as the sharp features are worn down.
(ii) Rift Valleys and Block Mountains
Block mountains: Formed by the uplift of crustal blocks along faults. Uplifted blocks are called horsts, and downthrown blocks are called grabens.
Rift valleys: These valleys are formed by the grabens, or downthrown blocks, that lie between the uplifted horsts.
(iii) Residual Mountains and Accordance of Summit Levels
Residual mountains: These mountains are formed when softer rocks surrounding harder rocks are eroded away, leaving the harder rocks standing as mountains.
Accordance of summit levels: The harder rocks forming residual mountains often have similar resistance to erosion, resulting in a consistent elevation for their summits.
(iv) Fold Mountains and Volcanic Activity
Fold mountains: Formed by the collision of tectonic plates, which can also trigger the release of magma from the Earth’s mantle, leading to volcanic activity.
Volcanic activity: The erupting magma forms volcanoes, which can be found within or near fold mountain ranges.
(v) Piedmont Alluvial Plains and Foothills
Piedmont alluvial plains: These plains are formed by the deposition of sediments carried by rivers flowing from mountains.
Foothills of mountains: Rivers originating from mountains carry sediments that are deposited at the base of the mountains, forming piedmont plains.
(vi) Volcanic Plateaus as ‘Plateaus of Accumulation’
Volcanic plateaus: These plateaus are formed by the accumulation of lava flows from volcanic eruptions.
Plateaus of accumulation: This term highlights that these plateaus are built up by the accumulation of volcanic material.
2. Brief Answers about Landforms
(a) Landform Development
Landforms develop over millions of years due to:
- Internal forces: Forces from within the Earth, like plate tectonics, causing mountains, volcanoes, and earthquakes.
- External forces: Forces from outside the Earth, like wind, water, and ice, causing erosion and weathering.
(b) Highest Landforms
The highest landforms are mountains. They are elevated landforms with steep slopes and a peak.
(c) Fold Mountain Formation
Fold mountains form when two tectonic plates collide, causing the Earth’s crust to buckle and fold under pressure, creating mountain ranges.
(d) Geosyncline
A geosyncline is a large, deep depression in the Earth’s crust where sediments accumulate over millions of years. These sediments are compressed and folded, eventually forming mountains.
(e) Piedmont Plain Example from India
The Gangetic Plain is a piedmont plain in India formed from the deposition of sediments carried by rivers flowing from the Himalayas.
(f) Rift Valley and Example from India
A rift valley is a low-lying area formed when tectonic plates move apart. The Narmada Valley in India is an example of a rift valley.
(g) Residual Mountain Formation
Residual mountains form when softer rocks surrounding harder rocks erode away, leaving the harder rocks standing as mountains.
(h) Plateau and its Types
A plateau is a flat, elevated area of land. The main types are:
- Intermontane plateaus: Located between mountains.
- Continental plateaus: Large, flat areas on continents.
- Volcanic plateaus: Formed by volcanic eruptions.
(i) Loess Plain Formation
Loess plains form from the accumulation of fine, wind-blown silt.
(j) Drift Plains and Example from Europe
Drift plains are formed by the deposition of glacial sediments. The North European Plain is an example.
(k) Structural Plain
A structural plain is a flat area formed by the erosion of horizontal layers of sedimentary rocks.
2. Reasons for Rock Characteristics (HOTS)
(a) Igneous Rocks as Primary Rocks
Igneous rocks are called primary rocks because they are formed directly from the cooling and solidification of molten magma or lava. They are the original rocks from which other rock types are derived.
(b) Large Crystals in Plutonic Rocks
Plutonic rocks, formed from the slow cooling of magma deep underground, have large crystals because they have ample time to grow.
(c) Sedimentary Rocks from Other Rocks
Sedimentary rocks are formed from the weathering and erosion of pre-existing rocks. These fragments are transported, deposited, and then cemented together to form new rocks.
(d) Fossils in Sedimentary Rocks
Fossils are usually found in sedimentary rocks because they are formed from the accumulation of sediments that can preserve the remains of organisms.
(e) Silicates as Common Rock-Forming Minerals
Silicates are the most common rock-forming minerals because they are abundant in the Earth’s crust and mantle. They are composed of silicon and oxygen, the most abundant elements in the Earth’s crust.
(f) Stratification in Sedimentary Rocks
Sedimentary rocks are stratified because they are formed in layers. Each layer represents a different period of deposition.
(g) Metamorphic Rocks as ‘Altered’ Rocks
Metamorphic rocks are called ‘altered’ rocks because they are formed from the transformation of pre-existing rocks due to heat, pressure, or chemical reactions.
(h) Basalt as a Basic Igneous Rock
Basalt is a basic igneous rock because it is rich in magnesium and iron, making it dark in color.
3. Brief Answers about Rocks
(a) Rocks and their Types
Rocks are naturally occurring solid materials made up of one or more minerals. The three main types of rocks are:
- Igneous rocks: Formed from the cooling and solidification of magma or lava.
- Sedimentary rocks: Formed from the accumulation and cementation of sediments.
- Metamorphic rocks: Formed from the transformation of existing rocks due to heat, pressure, or chemical reactions.
(b) Igneous Rock Formation
Igneous rocks form when molten rock (magma or lava) cools and solidifies.
(c) Hypabyssal Rocks and Examples
Hypabyssal rocks are igneous rocks that form when magma cools and solidifies at a depth of less than 2 km. Examples include:
- Dolerite
- Diorite
(d) Volcanic Rocks and their Characteristics
Two volcanic rocks are:
- Basalt: Dark-colored, fine-grained, and rich in magnesium and iron.
- Rhyolite: Light-colored, fine-grained, and rich in silica.
Volcanic rocks are generally fine-grained because they cool quickly on the Earth’s surface.
(e) Diagenesis and its Processes
Diagenesis is the process of physical and chemical changes that occur in sediments after deposition and before lithification. Processes include:
- Compaction: The weight of overlying sediments compresses the sediments.
- Cementation: Minerals dissolved in groundwater precipitate between sediment grains, binding them together.
(f) Cementation Process
Cementation occurs when minerals dissolved in groundwater precipitate between sediment grains, binding them together.
(g) Rocks Associated with Fossil Fuels and their Formation
Sedimentary rocks, particularly shale, sandstone, and limestone, are associated with fossil fuels. They form from the accumulation and burial of organic matter, which is transformed into coal, oil, and natural gas over millions of years.
(h) Metamorphic Rock Formation
Metamorphic rocks form when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are transformed by heat, pressure, or chemical reactions.
(i) The Rock Cycle
The rock cycle is a continuous process in which rocks are transformed from one type to another through various geological processes. It involves the formation, weathering, erosion, deposition, burial, melting, and cooling of rocks.
(j) Rock Types Formed by Specific Processes
- The rapid cooling of lava on the surface of the Earth: Extrusive igneous rocks (e.g., basalt)
- The alteration of existing rocks by application of heat and/or pressure: Metamorphic rocks (e.g., marble, slate)
- The accumulation of remains of shells and skeletons of marine organisms: Sedimentary rocks (e.g., limestone)
- The slow cooling of magma at great depths underground: Intrusive igneous rocks (e.g., granite)