Subsidence is the gradual or sudden sinking of the ground surface. It happens when the material beneath the surface shifts, compresses, or collapses, and it affects nearly 19% of the global population today. While it occurs naturally in some settings, most subsidence is caused by human activity, particularly the pumping of groundwater from underground aquifers.
What Causes the Ground to Sink
The single biggest driver of land subsidence is groundwater extraction. When water is pumped from underground rock and sediment, the tiny spaces that once held that water compress under the weight of everything above them. Fine-grained sediments like clay and silt are especially vulnerable because once they compact, they don’t bounce back. The process is largely irreversible.
Beyond groundwater pumping, several other forces cause subsidence:
- Underground mining: Removing coal or other minerals leaves voids beneath the surface. These can produce a broad, bowl-shaped depression called trough subsidence, or a sudden, localized collapse known as sinkhole subsidence.
- Drainage of organic soils: When wetlands or peatlands are drained for agriculture, the exposed organic material decomposes and shrinks, lowering the land surface over time.
- Sinkholes: In areas with soluble bedrock like limestone, water slowly dissolves the rock and creates underground cavities that eventually collapse.
- Thawing permafrost: As frozen ground in Arctic and subarctic regions warms, the ice within it melts and the soil loses its structure, causing the surface to drop unevenly.
- Natural compaction: Newly deposited sediments, such as those in river deltas, gradually compress under their own weight over geological time.
How Fast Land Can Sink
Subsidence rates vary enormously depending on how aggressively groundwater is being pumped and what type of geology sits below. In Vietnam’s Mekong Delta, one of the most studied examples, the average sinking rate from groundwater extraction is about 1.1 centimeters per year, with some areas exceeding 2.5 centimeters annually. Ho Chi Minh City, sitting at the delta’s edge, has recorded rates as high as 7 centimeters per year.
To put that in perspective, global sea levels rise roughly 3 millimeters per year. In many sinking regions, the land is dropping ten times faster than the ocean is climbing. That combination is devastating for coastal areas, where subsidence effectively amplifies flooding even without any change in sea level. The Chesapeake Bay region in the United States, for instance, experiences about 2 millimeters per year of subsidence from ancient geological processes alone, and that contributes meaningfully to the area’s rising flood risk.
The Global Scale of the Problem
A satellite-based analysis from the United Nations University projects that 1.6 billion people will live on subsidence-affected land by 2040, with 86% of that at-risk population concentrated in Asia. Perhaps more alarming, 635 million people are expected to be living on land that sinks faster than sea levels rise, meaning their flood exposure is growing from below and above simultaneously.
Major cities in Indonesia, Mexico, China, and Iran are among the worst affected. Jakarta has sunk so dramatically from groundwater pumping that Indonesia is relocating its capital. Venice, Italy, remains one of the most visible examples of how even modest subsidence transforms a city’s relationship with water.
Signs of Subsidence in Buildings
For homeowners, subsidence typically announces itself through cracks and structural shifts that get worse over time. The earliest sign is often hairline cracks in interior plaster. As movement continues, more distinctive patterns appear: diagonal cracks spreading at roughly 45-degree angles from the corners of windows and doors, stair-step cracks that follow the mortar lines in brickwork, and horizontal cracks along walls that suggest serious structural stress.
Other signs are less obvious. Doors and windows that suddenly stick, jam, or won’t latch properly often point to a shifting foundation distorting their frames. Floors may develop a noticeable slope, with furniture leaning to one side or gaps opening between the floor and baseboards. Bay windows and home extensions are particularly vulnerable because they often sit on shallower foundations than the main structure. You might notice them pulling away from the house or cracking where they connect to it.
Outside, dips or holes appearing in a driveway or yard near the foundation can indicate that soil is washing away or compacting beneath the surface, leaving unsupported voids that may lead to sudden settling. Not every crack signals subsidence (many result from normal seasonal expansion and contraction), but cracks that are wider than about 3 millimeters, that keep growing, or that appear in diagonal or stair-step patterns warrant investigation.
Subsidence in Spinal Surgery
The term “subsidence” also appears in orthopedic medicine, where it describes something mechanically similar: a harder object sinking into a softer one. After spinal fusion surgery, a cage or graft placed between two vertebrae can gradually press into the softer bone of the vertebral body above or below it. Surgeons define clinically significant subsidence as 2 or more millimeters of migration into the bone.
When this happens, the space between the vertebrae narrows, potentially undoing the correction the surgery was meant to achieve. The spine can develop an abnormal forward curve, and the hardware (plates and screws) holding everything in place can loosen or even break.
Several factors raise the risk. Older age, higher body weight, and osteoporosis all make it more likely. In lumbar spine fusions, the placement of the cage within the disc space matters considerably. Research published in Global Spine Journal found that cage positioning was the single strongest independent predictor, contributing over half of the overall risk. Patients with weakened bone density accounted for about 15% of the risk, with age and body weight playing smaller but measurable roles. Surgeons manage this risk by optimizing cage placement, selecting appropriately sized implants, and accounting for bone quality before the procedure.