---
title: "Subsidence | Intro to Geology"
description: "Subsidence is the gradual sinking of Earth's surface from sediment compaction, groundwater loss, or mining, and it's a major geologic hazard in Intro to Geology."
canonical: "https://fiveable.me/introduction-geology/key-terms/subsidence"
type: "key-term"
subject: "Intro to Geology"
unit: "Unit 15"
---

# Subsidence | Intro to Geology

## Definition

Subsidence is the gradual sinking of the ground surface in Intro to Geology, usually from sediment compaction, groundwater withdrawal, or underground mining. It matters because it changes land stability and hazard risk.

## What It Is

Subsidence is the gradual sinking or settling of the ground surface in Intro to Geology. It can happen slowly over years or become noticeable after a human activity changes what is holding the ground up.

A common natural cause is sediment compaction. When loose sediment is first deposited, it has lots of pore space between grains. Over time, the weight of overlying material squeezes those grains closer together, so the land surface lowers.

Human activity can speed this up. If groundwater is pumped out of an aquifer, the water that helped support the sediment is removed. The grains pack tighter, the ground drops, and you may see cracks in pavement, tilted buildings, or uneven roads.

Subsidence is not the same as a sudden collapse. It is usually a gradual downward movement of the land, which makes it easy to miss at first. That slow change is part of why it becomes a hazard, especially in cities built on soft sediments, reclaimed land, or coastal plains.

In geology classes, subsidence often shows up when you connect Earth's surface processes to human land use. A region can have stable bedrock nearby and still sink if the shallow sediment is compacting or if pumping lowers underground water pressure. In other words, the surface you walk on is not always fixed, even if the landscape looks calm.

Subsidence also matters in places shaped by karst topography, where limestone dissolves underground and can leave empty spaces. In those settings, sinking can range from broad settling to sudden sinkholes, depending on how the subsurface material changes.

## Why It Matters

Subsidence shows how geologic hazards are not just about dramatic events like earthquakes or eruptions. In Intro to Geology, it is one of the clearest examples of slow ground failure that still causes real damage to houses, roads, pipelines, drainage systems, and coastal infrastructure.

It also connects Earth processes to human decisions. If a city depends heavily on groundwater, the surface may sink because water withdrawal changes the pressure inside sediment layers. That makes subsidence a useful case for environmental geology, because the hazard is tied to resource use as much as to natural conditions.

This term also helps you read hazard maps and case studies more carefully. If an area sits on soft sediment, reclaimed land, or carbonate rock, you can ask what might happen to the land surface over time and whether flooding or cracking will get worse. Subsidence often works together with other hazards, especially landslides and flooding, so it is part of the bigger risk-assessment picture.

## Connections

### [Land subsidence](/introduction-geology/key-terms/land-subsidence)

Land subsidence is the broader phrase for the sinking of ground at the surface, and it is often the exact form of subsidence you see in city or coastal settings. In geology, the word usually points to measurable lowering of the land rather than just a local crack or small slump. You may see it discussed with mapping, elevation change, and infrastructure damage.

### Groundwater depletion

Groundwater depletion is one of the main human causes of subsidence. When water is pumped out of an aquifer, the sediment can compact more tightly, especially in fine-grained deposits like clay and silt. That means a water resource issue can turn into a land stability issue, which is why these topics are often studied together in environmental geology.

### Karst topography

Karst topography can produce subsidence when groundwater dissolves limestone underground and leaves open spaces behind. The sinking may be broad and gradual, or it may become a sudden collapse if the roof of a cavity fails. This connection is useful because it shows that not all subsidence comes from compaction, some comes from rock dissolution.

### [Slope stability](/introduction-geology/key-terms/slope-stability)

Slope stability focuses on whether a hillside stays in place or fails as a landslide. Subsidence is different because the movement is mainly downward settling, not downslope sliding, but both can damage structures and reshape the land. In hazard analysis, a weakened or changing ground surface can increase the chance of slope failure later.

## On the AP Exam

A quiz question might show a photo of cracked pavement, tilted utility poles, or a lowering coastline and ask you to identify subsidence as the process causing it. In lab work, you might compare elevation measurements over time, look at groundwater withdrawal data, or interpret a map of land-surface lowering. On short answers, the move is to explain the mechanism, sediment compaction, water removal, or underground voids, and then connect it to a real hazard like flooding or building damage. If a case study mentions a city sinking after heavy pumping, you should trace the cause from subsurface change to surface impact.

## Subsidence vs sinkhole

Subsidence is the broader sinking or settling of the ground, usually over a wider area and often gradually. A sinkhole is a specific, often more abrupt collapse that creates a localized hole, commonly in karst terrain. A sinkhole can be a type of subsidence, but not every case of subsidence becomes a sinkhole.

## Key Takeaways

- Subsidence is the gradual sinking of Earth's surface, not a sudden shake or slide.
- In Intro to Geology, the two big causes are sediment compaction and human groundwater withdrawal.
- Subsidence matters because it can damage roads, buildings, pipelines, and drainage systems.
- It is a hazard term you use when linking subsurface change to surface risk, especially in cities and coastal areas.
- Karst terrain, soft sediments, and heavy pumping are all settings where subsidence becomes more likely.

## FAQs

### What is subsidence in Intro to Geology?

Subsidence is the gradual lowering of the land surface. In Intro to Geology, you usually see it explained through sediment compaction, groundwater withdrawal, or underground mining. The big idea is that something below the surface changes, and the ground above settles downward.

### What causes subsidence?

The most common causes are compaction of loose sediment, removal of groundwater from aquifers, and collapse of underground spaces made by mining or dissolution. Soft, water-rich sediments are especially vulnerable because they can compress more easily when pressure changes. Coastal and low-lying areas often feel the impact most strongly.

### How is subsidence different from a sinkhole?

Subsidence is the general sinking or settling of land, often over a wider area and over a longer time. A sinkhole is a specific collapse, usually sudden and localized, that leaves a visible depression or hole. In karst landscapes, a sinkhole can happen as part of a subsidence process, but the terms are not interchangeable.

### Why does groundwater pumping cause subsidence?

Groundwater helps support the pore spaces between sediment grains. When too much water is pumped out, the grains can pack more tightly together, which lowers the ground surface. That is why places with heavy water use often watch for cracks, tilting structures, and changes in elevation.

## Related Study Guides

- [15.2 Natural hazards and risk assessment](/introduction-geology/unit-15/natural-hazards-risk-assessment/study-guide/WwkMN0wagR96748F)

## About This Document

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- [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns
- [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing
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