Landforms, Rocks, and the Rock Cycle: A Comprehensive Guide
Hi Mohi! Let’s break down these landform and rock questions.
1. Give Reasons for the following.
(i) Young fold mountains have a rugged topography but old fold mountains have gentler slopes.
- Young fold mountains: These mountains are relatively new and have been recently uplifted. They are still being shaped by erosion, resulting in sharp peaks, deep valleys, and rugged terrain.
- Old fold mountains: These mountains have been exposed to erosion for a longer period. Over time, the sharp peaks and deep valleys are worn down, leading to gentler slopes and rounded summits.
(ii) Rift valleys occur between block mountains.
- Block mountains: These mountains are formed when blocks of the Earth’s crust are uplifted along faults. The uplifted blocks are called horsts, and the downthrown blocks are called grabens.
- Rift valleys: The grabens, or downthrown blocks, form rift valleys between the uplifted horsts.
(iii) Residual mountains show an 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 that form residual mountains often have a similar resistance to erosion, leading to a consistent elevation for their summits.
(iv) Fold mountains are often associated with volcanic activity.
- Fold mountains: These mountains are formed by the collision of tectonic plates. The collision can also cause the release of magma from the Earth’s mantle, leading to volcanic activity.
- Volcanic activity: The magma can erupt through the surface, forming volcanoes, which can be found within or near fold mountain ranges.
(v) Piedmont alluvial plains lie on the foothills of mountains.
- Piedmont alluvial plains: These plains are formed by the deposition of sediments carried by rivers flowing from mountains.
- Foothills of mountains: The rivers originating from mountains carry sediments that are deposited at the base of the mountains, forming piedmont plains.
(vi) Volcanic plateaus are called ‘plateaus of accumulation’.
- Volcanic plateaus: These plateaus are formed by the accumulation of lava flows from volcanic eruptions.
- Plateaus of accumulation: The term ‘plateaus of accumulation’ refers to the fact that these plateaus are formed by the buildup of volcanic material.
2. Answer the following in brief
(a) How do landforms develop?
Landforms develop over millions of years due to:
- Internal forces: These forces come from within the Earth, like plate tectonics, causing mountains, volcanoes, and earthquakes.
- External forces: These forces come from outside the Earth, like wind, water, and ice, causing erosion and weathering.
(b) Which are the highest landforms? Define this type of landform.
The highest landforms are mountains. 🏔️ They are elevated landforms with steep slopes and a peak.
(c) How do fold mountains form?
Fold mountains form when two tectonic plates collide. The pressure forces the Earth’s crust to buckle and fold, creating mountain ranges.
(d) What is a 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) Give an example of a piedmont plain from India and briefly state how it formed.
The Gangetic Plain is a piedmont plain in India. It formed from the deposition of sediments carried by rivers flowing from the Himalayas.
(f) What is a rift valley? Give an example of such a valley 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) How do residual mountains form?
Residual mountains form when softer rocks surrounding harder rocks erode away, leaving the harder rocks standing as mountains.
(h) What is a plateau? What are the main types of plateaus?
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) How do loess plains form?
Loess plains form from the accumulation of fine, wind-blown silt.
(j) What are drift plains? Give an example from Europe.
Drift plains are formed by the deposition of glacial sediments. The North European Plain is an example.
(k) What is a structural plain?
A structural plain is a flat area formed by the erosion of horizontal layers of sedimentary rocks.
2. Give reasons for the following. [HOTS]
(a) Igneous rocks are known 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) Plutonic rocks have large crystals.
Plutonic rocks, formed from the slow cooling of magma deep underground, have large crystals because they have ample time to grow.
(c) Sedimentary rocks are formed 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) Only sedimentary rocks have fossils.
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 are the most 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) Sedimentary rocks are stratified.
Sedimentary rocks are stratified because they are formed in layers. Each layer represents a different period of deposition.
(g) Metamorphic rocks are called ‘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 is a basic igneous rock.
Basalt is a basic igneous rock because it is rich in magnesium and iron, making it dark in color.
3. Answer the given questions in brief.
(a) What are rocks? Mention the three types of rocks.
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) How do igneous rocks form?
Igneous rocks form when molten rock (magma or lava) cools and solidifies.
(c) What are hypabyssal rocks? Give two 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) Name any two volcanic rocks. State the characteristics of volcanic rocks.
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) What is diagenesis? Name the processes of diagenesis.
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) How does cementation take place?
Cementation occurs when minerals dissolved in groundwater precipitate between sediment grains, binding them together.
(g) Which rocks are associated with fossil fuels? How do they form?
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) How do metamorphic rocks form?
Metamorphic rocks form when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are transformed by heat, pressure, or chemical reactions.
(i) What is 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) Name the type of rocks formed by the following processes:
- (i) The rapid cooling of lava on the surface of the Earth: Extrusive igneous rocks (e.g., basalt)
- (ii) The alteration of existing rocks by application of heat and/or pressure: Metamorphic rocks (e.g., marble, slate)
- (iii) The accumulation of remains of shells and skeletons of marine organisms: Sedimentary rocks (e.g., limestone)
- (iv) The slow cooling of magma at great depths underground: Intrusive igneous rocks (e.g., granite)