Land subsidence

Also called: Subsidence · Topic: Natural Hazards and Disaster Management in India · NCERT: Class 11, Ch 6 "Natural Hazards and Disasters: Causes, Consequences and Management"

Meaning

Land subsidence means the ground surface sinks downward, either slowly or suddenly. It happens when the support beneath the ground is removed or squeezed together. NCERT's Table 6.1 lists it as a terrestrial (land-based) natural hazard. It matters because sinking ground cracks houses, roads and fields, and can force whole towns to move. Two Indian examples show this: the coal belts of the Damodar valley and Joshimath in 2023.

Explanation

How it works: support below is lost, so the surface drops

• The basic chain
• Something underground stops holding up the land above. This can be rock, coal, water or packed soil.
• An empty space or a weak layer forms below.

• The surface sinks into it. The sinking can be slow, or the ground can collapse suddenly.

• The ground mostly moves downward. In a landslide, it moves down a slope.

Four causes and their processes

Cause	Process	Example
Mining	Coal is dug out underground → empty spaces are left → the roof rock caves in	Jharia coalfield (Dhanbad, Jharkhand); Raniganj coalfield (West Bengal), both in the Damodar valley
Underground coal fires	Coal seams burn underground → the burnt-out space collapses	Jharia, where fires have burned for decades
Groundwater pumping	Too much water is pumped out → pore spaces in clay and silt close up → the land sinks	Fast-growing cities on alluvial plains
Natural collapse	Limestone dissolves underground, or loose old debris settles	Karst areas; towns built on old landslide debris

• Pore spaces are the tiny gaps between grains of soil. Water fills them and helps hold up the ground. When the water is removed, clay and silt pack tighter and the surface drops.
• Karst topography means limestone land where rainwater slowly dissolves the rock. This forms caves and sinkholes (pits where the surface falls into a hollow below).

Conditions that make subsidence likely

• Empty spaces underground: old mine workings, burnt coal seams or dissolved limestone.
• Soft, loose ground: clay, silt, or unconsolidated debris (loose material that is not packed together).
• Water getting in: poor drainage and no sewer system let water seep into the ground. This weakens loose material.
• Extra load and disturbance: heavy, unplanned buildings on top, and tunnelling or road cutting nearby.

Where it occurs

• Coal-mining belts of the Peninsular plateau
• Jharia coalfield (Dhanbad, Jharkhand): subsidence from mining and underground coal fires.
• Raniganj coalfield (West Bengal): subsidence from mining.

• Both lie in the Damodar valley.

• Mining-and-subsidence landslides (NCERT, moderate-to-low zone): Jharkhand, Odisha, Chhattisgarh, Madhya Pradesh, Maharashtra, Andhra Pradesh, Karnataka, Tamil Nadu, Goa and Kerala.

• Himalayan hill town: Joshimath (2023)
• Place: Chamoli district, Uttarakhand. The town sits above the Alaknanda valley and is a gateway to Badrinath and Auli.
• What happened: in January 2023, wide cracks opened in houses, roads and fields. A strip of land about 350 metres wide was affected [2].
• Relief: at a high-level review on 8 January 2023, it was reported that one NDRF team and four SDRF teams had reached the town [2]. The district administration moved affected families to safer places [2]. In total, hundreds of families were relocated.
• Why it happened:
  • The town is built on old landslide debris, which settles easily.
  • Poor drainage and no proper sewer system let water seep into the ground.
  • Heavy, unplanned building put extra load on the slope.
  • Tunnelling for the nearby Tapovan-Vishnugad hydropower project and road work disturbed the slope.
• Response: the State Government stopped all building work in the Joshimath area. This included the Tapovan-Vishnugad power project and the Helang-Marwari bypass road [3].

• Monitoring: ISRO satellite data showed the ground sinking fast in the weeks around January 2023.

• Alluvial plains: fast-growing cities that pump too much groundwater.

• World: karst (limestone) regions, where rock dissolving underground leads to sinkholes.

Don't confuse with

• Landslide: a mass of rock, soil and debris slides down a slope along a failure plane (a surface of weakness). In subsidence, the ground sinks downward into a space below, and it can happen even on flat land, as in coalfields.
• Debris flow (Wayanad, 2024): mud, boulders and trees mixed with water rush down stream valleys like a river. It is fast, it flows sideways down valleys, and rain triggers it. Subsidence is the surface settling or collapsing in place.
• Sinkhole: one landform that subsidence creates in karst areas, where limestone has dissolved. Subsidence is the wider process, and it also includes mining, coal fires and groundwater pumping.
• Very high landslide zone: the Himalaya and Western Ghats. NCERT puts mining-and-subsidence landslides in the plateau states under the moderate-to-low zone.

Prelims Hooks

• NCERT's Table 6.1 classifies land subsidence as a terrestrial natural hazard. It is not atmospheric, aquatic or biological.
• Jharia = Jharkhand (Dhanbad) and Raniganj = West Bengal. Both are coalfields in the Damodar valley known for subsidence. Jharia also has coal fires that have burned for decades.
• Joshimath is in Chamoli district, not Pithoragarh or Rudraprayag. It sits above the Alaknanda valley. The linked project is Tapovan-Vishnugad [3].
• After the Joshimath crisis, building work was stopped, including the Helang-Marwari bypass road [3]. The affected strip was about 350 metres wide [2].
• Process–cause match: groundwater pumping causes pore spaces in clay and silt to close up. Karst causes limestone to dissolve. Mining causes the roof rock of empty mine spaces to cave in.
• Trap: the plateau states listed for mining-and-subsidence landslides (Jharkhand, Odisha, Chhattisgarh and others) fall in the moderate-to-low zone, not the very high zone.

Mains Points

• Two kinds of subsidence in India (GS-I)
• On the Peninsular plateau, the cause is human removal of material below ground: coal mining and coal fires at Jharia and Raniganj.

• In the Himalaya, the cause is weak ground under development pressure: Joshimath stands on old landslide debris and has poor drainage, heavy building and nearby tunnelling.

• Development versus fragility (GS-III)

• Joshimath shows how hydropower tunnels, roads and unplanned towns weaken unstable slopes.

• Answer frame: carrying-capacity studies for hill towns (how much building and population the land can safely bear); proper drainage and sewer systems; stricter environmental clearances for hydropower and highway projects; stopping work quickly when cracks appear [3]; satellite monitoring by ISRO.

• Mitigation in mining belts (GS-III)

• Sand stowing: filling old mine voids with sand so the roof does not cave in.
• Putting out underground coal fires.
• Resettling people who live over unstable ground.
• All of this fits the Sendai Framework shift from relief after a disaster to reducing risk before it.

Related concepts

• Landslide
• Landslide vulnerability zones
• Landslides in the Himalayas and Western Ghats
• Landslide mitigation
• Malpa landslide
• Landslide Atlas of India
• Joshimath land subsidence (2023)
• Wayanad landslides (2024)

Read more

• Landslides and land subsidence