Landforms and their Evolution
1. Multiple choice questions.
(i) In which of the following stages of landform development, downward cutting
is dominated?
(a) Youth stage (c) Early mature stage
(b) Late mature stage (d) Old stage
Answer: (a) Youth stage.
(ii) A deep valley characterised by steep step-like side slopes is known as
(a) U-shaped valley (c) Blind valley
(b) Gorge (d) Canyon
Answer: (d) Canyon.
(iii) In which one of the following regions the chemical weathering process is more dominant than the mechanical process?
(a) Humid region (c) Arid region
(b) Limestone region (d) Glacier region
Answer: (a) Humid region.
(iv) Which one of the following sentences best defines the term ‘Lapies’ ?
(a) A small to medium sized shallow depression
(b) A landform whose opening is more or less circular at the top and
funnel shaped towards bottom
(c) A landform formed due to dripping water from surface
(d) An irregular surface with sharp pinnacles, grooves and ridges
Answer: (d) An irregular surface with sharp pinnacles, grooves and ridges.
(v) A deep, long and wide trough or basin with very steep concave high walls at its head as well as in sides is known as:
(a) Cirque (c) Lateral Moraine
(b) Glacial valley (d) Esker
Answer: (a) Cirque.
2. Answer the following questions in about 30 words.
(i) What do incised meanders in rocks and meanders in plains of alluvium indicate?
Answer: They reveal the past! Incised meanders show rivers once flowed over harder rocks, now cut down to reveal their winding paths. Alluvial meanders tell of gentler past flows shaping softer plains. They paint a picture of rivers adapting to changing landscapes.
(ii) Explain the evolution of valley sinks or uvalas.
Answer: Sinkholes join forces! When dolines and swallow holes merge due to slumping or cave collapse, deeper, wider valleys called uvalas form. It's like nature's playground where smaller depressions combine to create a dramatic landscape feature.
(iii) Underground flow of water is more common than surface run-off in limestone areas. Why?
Answer: Limestone's the culprit! It dissolves easily in water, creating cracks and fissures. Like a maze for water, these hidden pathways draw it underground, making subsurface flow far more prevalent than surface streams in these areas. Think rivers flowing "inside" the rock!
(iv) Glacial valleys show up many linear depositional forms. Give their locations and names.
Answer: Across glacial valleys, keep an eye out for these linear friends:
*Drumlins: Elongated mounds of streamlined rock and till, often found in groups. Look for them in Ireland, Wisconsin, and Scandinavia.
*Eskers: Snake-like ridges of sand and gravel deposited by meltwater rivers. Check Alaska, Canada, and northern Europe for their winding paths.
*Lateral moraines: Long ridges of debris left behind by receding glaciers. You'll find them flanking glacial valleys in the Alps, Himalayas, and Andes.
Remember, these linear forms add a unique fingerprint to glacial landscapes, telling stories of ice and meltwater that once sculpted the land.
(v) How does wind perform its task in desert areas? Is it the only agent responsible for the erosional features in the deserts?
Answer: In deserts, wind is a master sculptor! It:
*Deflates: Picks up and removes loose sand, carving out depressions and exposing rock formations.
*Abrades: Sand acts like sandpaper, polishing rocks and creating sculpted features like ventifacts.
*Builds dunes: Piles up transported sand into rippling waves and towering formations.
However, wind has some helpmates:
*Water: Flash floods can carve canyons and deposit sediments, shaping landscapes.
*Temperature: Extreme swings cause rock cracking and expansion, leading to erosion.
While wind dominates, deserts are shaped by a team effort of nature's forces!
3. Answer the following questions in about 150 words.
(i) Running water is by far the most dominating geomorphic agent in shaping the earth’s surface in humid as well as in arid climates. Explain.
Answer: You're absolutely right! Running water reigns supreme as Earth's landscape sculptor, dominating both humid and arid environments, and here's why:
Humid Regions:
*Abundant rainfall: Provides high energy for erosion and transportation of rocks and sediments.
*Varied flow: Creates diverse landforms like rivers, valleys, deltas, and waterfalls.
*Chemical weathering: Enhances erosion by breaking down rocks.
Arid Regions:
*Flash floods: Powerful bursts of water cause sudden and dramatic erosion.
*Windblown sand: Acts as an abrasive tool, sculpting rock formations.
*Ephemeral rivers: Though temporary, can still carve canyons and deposit sediments.
Dominant Features:
*Erosion: Running water excels at removing and transporting materials, shaping landscapes through valleys, canyons, and plains.
*Deposition: From fertile floodplains to deltas, running water lays down sediments, creating new landforms.
*Continuous Activity: Unlike other agents like wind or glaciers, running water is constantly flowing, ensuring its persistent impact on the landscape.
Therefore, regardless of climate, running water's ability to erode, transport, and deposit materials makes it the undisputed champion of shaping our planet's surface, leaving its mark on everything from lush valleys to arid canyons. It's like Earth's tireless sculptor, constantly reshaping the canvas of our planet with every drop of water that flows.
(ii) Limestones behave differently in humid and arid climates. Why? What is the dominant and almost exclusive geomorphic process in limestone areas and what are its results?
Answer: Limestone's unique chemistry makes it behave differently in humid and arid climates:
Humid Climates:
*Abundant water: Dissolves limestone through carbonic acid, creating:
.Sinkholes: Collapsing ground due to dissolved rock beneath.
.Caves: Underground cavities formed by dissolving water.
.Karst topography: Landscape characterized by sinkholes, caves, and disappearing streams.
Arid Climates:
*Limited water: Less dissolving, but mechanical weathering (like temperature fluctuations) still occurs.
*Karst features less prominent: Fewer sinkholes and caves due to lack of water-driven dissolution.
*Surface features: Limestone pavements (exposed bedrock) and sculpted rock formations are more common.
Dominant Process:
The dominant and almost exclusive geomorphic process in limestone areas is dissolution, driven by water in humid climates. This results in:
*Chemical erosion: Dissolving and removal of limestone, creating cavities and shaping karst features.
*Deposition: Dissolved minerals can precipitate elsewhere, forming speleothems in caves like stalactites and stalagmites.
*Unstable ground: Sinkholes can pose hazard risks due to sudden collapses.
Therefore, understanding how water availability influences dissolution makes the unique behavior of limestone in different climates clear. While arid regions see less dramatic karst landscapes, the sculpting power of water remains the key driver in shaping these fascinating rock formations.
(iii) How do glaciers accomplish the work of reducing high mountains into low hills and plains?
Answer: Glaciers are Earth's bulldozers, transforming soaring mountains into gentle hills and plains through a relentless combination of:
Erosion:
*Abrasion: Like sandpaper on rock, glaciers drag along massive amounts of debris, scraping and wearing down mountainsides.
*Plucking: The sheer weight and movement of a glacier can pry off large chunks of rock, further reducing mountain mass.
*Weathering: Meltwater freezes and thaws within cracks, expanding and weakening the rock, making it easier to erode.
Transportation:
*Glacial valleys: As glaciers carve their paths, they deepen and widen valleys, eventually creating U-shaped valleys with smoothed sides.
*Transported debris: Rocks, sand, and soil are carried vast distances, eventually being deposited as moraines (ridges of material) or filling valleys and plains.
Deposition:
*Moraines: These ridges and piles of debris deposited by the glacier can eventually form new landforms like hills or low plains.
*Outwash plains: When meltwater washes out finer sediments from beneath the glacier, it deposits them as flat, fertile plains.
Over time, these processes grind away at mountains, reducing their height and filling in valleys. The gradual deposition of eroded material creates new, lower landforms, ultimately transforming rugged terrain into gentler hills and plains.
