Landforms on contours

Detail

Basic ideas you need before reading any landform

• Contour: a line on a map that joins places of the same height above mean sea level.
• Contour interval: the fixed difference in height between two contours next to each other.
• Spacing tells slope. This is the main rule.
• Contours close together mean the ground rises a lot over a short distance, so the slope is steep.
• Contours far apart mean the ground rises slowly over a long distance, so the slope is gentle.

• Contours that merge into one line mean the drop is almost vertical. This happens only at a cliff or a waterfall.

• Shape tells the landform. Closed rings show a hill or a plateau. V or U bends show a valley or a spur.

• Values tell direction. Check whether the numbers rise or fall towards the centre or the apex. Two landforms can have the same shape on the map, and only the values tell them apart.
• Where contours appear on Indian sheets:
• The National Map Policy, 2005 created two series of Survey of India maps: Defence Series Maps (DSMs) and Open Series Maps (OSMs) [2].
• DSMs are on Everest/WGS-84 datum and Polyconic/UTM projection, at various scales. They carry heights, contours and full content without dilution of accuracy. They are classified, and the Ministry of Defence makes the rules for their use [2].
• OSMs are made only by the Survey of India, on UTM projection and WGS-84 datum, with sheet numbers different from the DSMs. They become "Unrestricted" after a one-time clearance from the Ministry of Defence [2].
• In an OSM, the Relief/Hypsography layer includes contours with sub-features, sand features, ice forms, spot heights, approximate heights and benchmarks [2].
• Contours and heights are left out of OSMs in restricted zones, on the Ministry of Defence's instructions [2]. So a student may find no relief on some sheets of border or sensitive areas.
• OSMs at 1:50,000 can be downloaded as free PDFs from the Survey of India online maps portal, by sheet number or by state and district [3].

Conical hill

• Definition: a hill that rises evenly on all sides to a narrow top.
• On the map:
• Contours are nearly circular, one inside another (concentric).
• They are evenly spaced, because the slope is the same all the way up.

• The highest value is at the centre. Values fall outwards.

• Trap: a depression (a hollow) also shows as closed rings. But there the values fall towards the centre.

• Example: volcanic cones, such as Barren Island in the Andaman Sea, India's only active volcano.

Plateau

• Definition: a broad, flat-topped highland with fairly steep sides. It is often called a tableland.
• On the map:
• Contours are crowded at the edges, which shows the steep sides.
• The innermost contour encloses a wide area, which shows the flat top.

• There are few or no contours on the top, because the height hardly changes there.

• Examples in India: the Deccan Plateau, the Chota Nagpur Plateau (Jharkhand), the Malwa Plateau (Madhya Pradesh) and the Meghalaya Plateau.

Feature	Contour shape	Spacing	Innermost contour
Conical hill	Concentric, nearly circular	Even from base to top	Small ring, highest value
Plateau	Closed, often irregular	Crowded at edges, wide gap on top	Encloses a wide area

Spur

• Definition: a tongue of high land pushing out from a hill or ridge into lower ground.
• On the map:
• Contours form a V (or a rounded U).
• The apex of the V points to lower ground, and the arms point back to higher ground.

• This is the reverse of a valley.

• How to tell a spur from a valley:

• Read the values. At a spur, the contour values fall towards the apex.

• At a valley, the values rise towards the apex.

• Where seen: spurs and valleys usually alternate along Himalayan hillsides. Roads and villages often sit on spurs, which stand above the valley floors.

Cliff

• Definition: an almost vertical rock face.
• On the map:
• Contours run very close together.

• At the cliff, they merge into one line.

• Process:

• The rock face is so steep that several heights lie on almost the same horizontal spot.

• So the contours for those heights cannot be drawn apart. They join into one line.

• Examples: sea cliffs on the Konkan coast, and the scarps of the Western Ghats that face the Arabian Sea.

Valleys

How valleys form is covered under landforms-evolution. This section covers only how they look on contours.

• Valley: a long, low area between higher land, usually with a river or glacier.
• Common rule: where a contour crosses a valley, it bends into a V or U. The apex points upstream, towards higher ground.

V-shaped valley (mountain rivers)

• Process:
• A young mountain river flows fast down a steep slope.
• It cuts its bed downwards (vertical erosion: the river cuts deeper rather than wider).

• The result is a narrow valley with steep sides, shaped like a V.

• On the map:

• The contours form a V.
• The innermost contour has the lowest value and a very narrow gap.

• The apex of the V points upstream, towards higher ground.

• Examples: Himalayan river valleys in their upper courses.

U-shaped valley (glacial)

• Process:
• A glacier (a slow river of ice) fills the whole valley.
• It grinds both the floor and the sides.

• The result is a flat, wide floor with steep sides.

• On the map: the innermost contour has a wide gap, which shows the flat floor. The contours on the sides are close, which shows the steep walls.

• Examples: glaciated valleys of the Greater Himalaya, such as parts of Ladakh and Himachal Pradesh.

Gorge

• Definition: a deep, narrow valley with very steep sides.
• Process: it forms where the river cuts down faster than it cuts sideways (vertical erosion is greater than lateral erosion).
• On the map: the contours are very close, with a narrow innermost gap.
• Examples: the Marble Rocks gorge of the Narmada at Bhedaghat near Jabalpur (Madhya Pradesh), and the deep Himalayan gorges of the Indus, Sutlej and Brahmaputra (Dihang).

Valley type	Agent	Floor	Innermost contour gap	Spacing on sides
V-shaped	Mountain river	Narrow	Very narrow, lowest value	Close
U-shaped	Glacier	Flat, wide	Wide	Close (steep walls)
Gorge	River (vertical erosion much greater than lateral)	Very narrow	Narrow	Very close

Waterfall

• Definition: a sudden, nearly vertical drop of river water.
• On the map: contours merge where they cross the stream. It is like a cliff, but on the river line.
• Examples: Jog Falls on the Sharavati (Karnataka), and Dhuandhar Falls on the Narmada at Bhedaghat (Madhya Pradesh).

Rapids

• Definition: fast, cascading stretches of a river (the water tumbles over rocks in a series of small steps). They lie just above or below a waterfall.
• On the map: contours cross the stream at wider spacing than at the fall, but they are still closer than on the normal river course.
• Waterfall vs rapids:
• Contours that merge on the stream show a waterfall.
• Contours that are close but separate on the stream show rapids.

Exam skill (NCERT Exercise A)

From a contour sketch, you must give three answers:

1. Name the feature. - Closed rings: a hill if the values rise inwards, a plateau if the top is wide, a depression if the values fall inwards. - V or U bends: a valley if the values rise towards the apex, a spur if the values fall towards the apex. - Merged lines: a cliff, or a waterfall if they are on a stream.

2. Give the direction of river flow. - The apex of the V points upstream. - So the river flows away from the apex, towards the open end of the V and the lower contour values.

3. Name the type of slope. - Even spacing: uniform. - Close spacing: steep. - Wide spacing: gentle. - Close at the top and wide at the bottom: concave. - Wide at the top and close at the bottom: convex.

Prelims Hooks

• Contours merging into one line show only a cliff or a waterfall. A waterfall is a merge on a stream.
• In a V-shaped valley, the V's apex points upstream. In a spur, the apex points to lower ground. The two are reverse patterns.
• Valley vs spur trap: both show V-shaped contours. Valley values rise towards the apex, and spur values fall towards it.
• Conical hill vs plateau: both have closed contours. Only the plateau's innermost contour encloses a wide area.
• U-shaped valley: made by a glacier, with a wide innermost gap. Gorge: made by a river, with a narrow innermost gap and very close contours.
• Rapids show contours crossing the stream at wider spacing than at a waterfall.
• The National Map Policy, 2005 created DSMs (classified, Ministry of Defence rules) and OSMs (UTM projection, WGS-84 datum, unrestricted after one-time Ministry of Defence clearance) [2].
• On OSMs, contours and heights are not shown in restricted zones [2].
• The OSM Relief/Hypsography layer includes contours, sand features, ice forms, spot heights and benchmarks [2].
• Gorge–river–state pair: Marble Rocks, Bhedaghat – Narmada – Madhya Pradesh.

Mains Points

• Contours as a planning tool (GS-I/GS-III):
• Contour spacing shows steep slopes, cliffs and gorges.
• Planners use this to place roads, railway alignments, dams and terraced farms.

• Gorges and waterfalls mark good hydropower and dam sites, because the river drops sharply over a short distance.

• Disaster risk (GS-III):

• Very close contours and cliffs in the Himalaya and the Western Ghats mark landslide-prone slopes.
• Narrow V-shaped valleys and gorges carry floods quickly downstream.

• Reading contours helps with hazard zoning and with choosing safe places for settlements, such as spurs rather than valley floors.

• Balancing security and open data:

• The National Map Policy, 2005 split maps into classified DSMs and public OSMs to protect national security [2].
• Contours and heights are removed from OSMs in restricted zones [2], which limits relief data in border regions.
• Free 1:50,000 OSM PDFs [3] widen access for development planning, education and disaster management.