--- title: "Land Subsidence | Intro to Geology" description: "Land subsidence is the sinking of Earth's surface from rock collapse, groundwater loss, or compaction, especially in karst areas studied in Intro to Geology." canonical: "https://fiveable.me/introduction-geology/key-terms/land-subsidence" type: "key-term" subject: "Intro to Geology" unit: "Unit 13" --- # Land Subsidence | Intro to Geology ## Definition Land subsidence is the gradual sinking of the ground surface in Intro to Geology, usually from groundwater withdrawal, sediment compaction, or karst collapse. It often shows up where soluble rock has been dissolved underground. ## What It Is Land subsidence is the downward settling or sinking of Earth's surface when the material below it loses support. In Intro to Geology, you usually meet it as a surface expression of what is happening underground, such as water leaving pores in sediment, rock dissolving, or empty spaces forming and collapsing. The simplest way to picture it is this: the ground looks solid, but it is really a stack of grains, fractures, and voids. If the material below is compacted or removed, the surface can drop. That sinking may happen slowly over years or suddenly as a collapse, depending on what caused the support to disappear. One common cause is groundwater depletion. When water is pumped out of an aquifer, the grains in the sediment are no longer pushed apart by pore pressure, so they pack more tightly. Fine-grained sediments are especially prone to this because once they compact, they do not bounce back very well. That is why heavily irrigated or heavily pumped regions can sink over time. Another big geology connection is karst terrain. In karst landscapes, slightly acidic groundwater dissolves soluble bedrock such as limestone. As the rock is removed, caves, cavities, and voids can form underground. If the roof of a cavity weakens enough, the surface can sag or collapse, creating sinkholes or broader subsidence around them. Subsidence is not always dramatic, which is what makes it tricky. A region may lose a few centimeters at a time and still end up with cracked foundations, broken roads, tilted sidewalks, or drainage problems. In low-lying places, even a small drop in elevation can increase flooding because the land no longer sits as high above nearby water. For geology, the term connects surface landforms to subsurface processes. You are not just naming a sinking area, you are tracing the cause, whether that is compaction, extraction, dissolution, or collapse. That link between underground change and surface change is exactly why subsidence belongs in the karst and groundwater parts of the course. ## Why It Matters Land subsidence shows how Intro to Geology connects rocks, water, and human activity to real landscape change. It is one of the clearest examples of a hidden process shaping the surface you can actually see. This term helps you make sense of karst topography, because subsidence is often what happens when limestone dissolves and support is lost underground. It also ties into groundwater topics, since pumping water out of an aquifer can compact sediments and lower the ground. Those are two different mechanisms, but both end in the same surface result: the land drops. It also shows up in environmental geology, where people need to think about hazards before building roads, houses, canals, or pipelines. A city built on subsiding ground may have repeated cracking, drainage trouble, or flood risk even if the weather has not changed. That makes subsidence a useful term for interpreting maps, hazard reports, and case studies. If you can identify subsidence, you can usually trace the chain of evidence backward. Is the area made of soluble rock? Has groundwater been heavily pumped? Are sinkholes appearing? Those clues help you explain not just what happened, but why the landscape is changing. ## Connections ### karst topography Land subsidence is one of the surface outcomes of karst processes. In karst areas, groundwater dissolves soluble bedrock like limestone, which can leave voids underground. When those voids get large enough, the surface may settle, sag, or collapse. So if you see subsidence in a karst setting, you are usually looking at the end result of chemical weathering below ground. ### sinkhole A sinkhole is a specific kind of collapse or depression, while land subsidence is the broader sinking of the ground. Some sinkholes form suddenly when a cavity roof fails, but other times the surface lowers gradually first. In Intro to Geology, you can think of sinkholes as one dramatic possible outcome of the same processes that cause subsidence. ### groundwater depletion Groundwater depletion often causes subsidence in sediment-filled basins and irrigated regions. When water is removed faster than it is replaced, pore pressure drops and the grains in the sediment compact. That lowers the ground surface even if the land itself is not collapsing into a cave. This connection is a common example of how water management changes geology at the surface. ### [carbonic acid](/introduction-geology/key-terms/carbonic-acid) Carbonic acid is the weak acid that forms when water mixes with carbon dioxide, and it is the chemical driver behind limestone dissolution in karst settings. It does not cause subsidence directly, but it helps create the voids and weakened rock that can lead to it. If you understand carbonic acid, karst subsidence makes a lot more sense. ## On the AP Exam A quiz question might ask you to match a flooded, sinking city district with the process causing it, or to explain why a karst region has sudden surface depressions. In a lab or map exercise, you may need to identify subsidence from contour changes, cracks, sinkholes, or lowered land elevation over time. In a short response, the strongest answer usually traces cause and effect: groundwater pumping or rock dissolution leads to loss of support, then the surface settles or collapses. If a problem gives you a limestone area, subsidence often points you toward karst. If it gives you irrigated farmland or a heavily pumped aquifer, compaction from groundwater depletion is the better explanation. ## land subsidence vs sinkhole Land subsidence and sinkholes are related, but they are not the same thing. Subsidence is the broader sinking or settling of the ground, which can happen slowly and over a wide area. A sinkhole is a more specific depression or collapse, often forming when a void opens in karst terrain. A sinkhole can be part of subsidence, but not every subsiding area makes a sinkhole. ## Key Takeaways - Land subsidence is the sinking of Earth's surface because the material below it loses support. - In Intro to Geology, subsidence often comes from groundwater withdrawal, sediment compaction, or karst collapse. - Karst regions are especially vulnerable because dissolving limestone can leave caves and voids underground. - Subsidence can crack buildings, damage roads, change drainage, and increase flooding risk. - If you can trace the cause underground, you can usually explain the pattern of sinking at the surface. ## FAQs ### What is land subsidence in Intro to Geology? Land subsidence is the gradual sinking or settling of the ground surface. In Intro to Geology, it usually happens when groundwater is removed, sediment compacts, or rock dissolves in karst terrain. The main idea is that the surface drops because support below it changes. ### What causes land subsidence? The biggest causes are groundwater depletion, extraction of oil or natural gas, sediment compaction, and dissolution of soluble rock such as limestone. In karst areas, subsidence may be linked to caves or sinkholes underground. In sedimentary basins, it often comes from losing pore pressure after heavy pumping. ### Is land subsidence the same as a sinkhole? No. A sinkhole is a specific type of depression or collapse, often in karst topography. Land subsidence is the broader term for ground sinking, which can happen slowly over a large area or suddenly in one spot. A sinkhole can be one result of subsidence, but not the whole concept. ### Why does groundwater pumping cause the ground to sink? When water is pumped out of pore spaces in sediment, the grains get packed more tightly together. That compaction lowers the land surface. This is especially common in fine-grained sediments, where the loss of water support can cause the ground to settle for a long time. ## Related Study Guides - [13.3 Karst topography and cave formation](/introduction-geology/unit-13/karst-topography-cave-formation/study-guide/86oQ9iEiYMsKslxP) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [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 - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/introduction-geology/key-terms/land-subsidence#resource","name":"Land Subsidence | Intro to Geology","url":"https://fiveable.me/introduction-geology/key-terms/land-subsidence","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/introduction-geology/key-terms/land-subsidence#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:22:42.379Z","isPartOf":{"@type":"Collection","name":"Intro to Geology Key Terms","url":"https://fiveable.me/introduction-geology/key-terms"},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/introduction-geology/key-terms/land-subsidence#term","name":"land subsidence","description":"Land subsidence is the gradual sinking of the ground surface in Intro to Geology, usually from groundwater withdrawal, sediment compaction, or karst collapse. 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