Undermining is the removal or weakening of material beneath a surface, structure, or system, causing what sits above to lose its support. In geology and engineering, it refers to the physical processes that hollow out or erode the ground from below, from waves gnawing at the base of a cliff to groundwater dissolving bedrock into sinkholes. In psychology, the term describes how external rewards can erode a person’s internal drive to do something they once found enjoyable on its own. What ties every usage together is the same basic idea: something is being eaten away from underneath, and the thing on top has not yet realized how unstable it has become.
Cliffs Eaten From Below
One of the most visible forms of undermining happens along rocky coastlines, where waves attack the base of a cliff and carve a horizontal notch into the rock face. Over time, the notch deepens, and the overhanging cliff above it is left unsupported. Eventually the weight becomes too much, and chunks of rock topple or shear off in what geologists call a mass-wasting event. Research using digital photogrammetry has confirmed this basic sequence: as a wave-cut notch enlarges, it changes the stress distribution in the cliff above, triggering progressive failure and causing the cliff face to retreat landward.1Geomorphology. Analysis of wave-cut notch formation using digital photogrammetry
The process is not driven by wave energy alone. Studies of limestone sea cliffs in Japan’s Ryukyu Islands show that tension cracks developing from the top of the cliff work in concert with the notch growing from the bottom. The cliff is being weakened from two directions simultaneously. When researchers compared field measurements of fallen blocks to the predictions of cantilever beam models, they found that toppling failures were best explained by the combined growth of both the basal notch and the vertical tension cracks, not either feature in isolation.2Geomorphology. Effect of the development of notches and tension cracks on instability of limestone coastal cliffs in the Ryukyus, Japan The takeaway is that a cliff can look solid from above while being deeply compromised below and cracked through the middle. Coastal undermining is a reminder that the most dangerous erosion is often the erosion you cannot see from the surface.
Hidden Voids and Soil Piping
Undermining does not require ocean waves. It can happen deep underground, wherever moving water is able to carry soil particles through the subsurface, leaving behind tunnels and voids. This process, called soil piping, occurs when water flowing through a soil mass exceeds a critical threshold of force on individual grains, dislodging and transporting them along preferential flow paths. Over time, these paths widen into pipe-like channels that can grow large enough to swallow the surface above them.
Modeling work has treated piping-prone soil as a two-phase system, with solid grains and flowing water interacting under conditions that combine erosion with the soil’s tendency to deform under stress. Once erosion begins, it is self-reinforcing: the removal of grains increases flow velocity through the void, which dislodges more grains, which enlarges the void further.3Acta Geotechnica. A coupled hydro-nested model for subsurface erosion with analyses of soil piping and void formation Dams, levees, and road embankments are particularly vulnerable because they sit on or are built from compacted soil with water flowing through or beneath them. The failure mode is insidious: the structure can appear perfectly intact until the moment the roof of an internal pipe collapses, at which point the damage is sudden and often catastrophic.
A related but distinct mechanism operates in carbonate terrain where warm groundwater dissolves limestone from below. Thermal surveys in karst regions have detected rising plumes of warm water, more than 2°C warmer than the surrounding aquifer, that dissolve the rock and create large voids and maze-like cave systems. When these voids reach a critical size, the surface above responds by sagging and eventually collapsing into sinkholes.4Geomorphology. Sagging and collapse sinkholes over hypogenic hydrothermal karst in a carbonate terrain Unlike soil piping, which is mechanical, this process is chemical: the rock itself is being dissolved. But the end result is the same. Support is removed from below, and the surface eventually gives way.
When Pumping Out Groundwater Makes the Land Sink
Some of the largest-scale undermining on Earth is happening right now beneath cities and farmland, driven not by natural erosion but by the sheer volume of groundwater humans are pumping out of underground aquifers. When water is extracted from the pore spaces between sediment grains in a confined aquifer, the weight of the overlying rock and soil compresses those grains together. If the compression exceeds a certain threshold, the sediment compacts permanently and the land surface above sinks. This is land subsidence, and in heavily pumped regions it operates at scales that are difficult to grasp.
In Cangzhou, China, severe overexploitation of a deep aquifer system has caused widespread subsidence. Modeling of the aquifer found that the permanent compression reduced the deep aquifer’s storage capacity by a staggering amount: for every meter that the confined water level dropped, roughly 220 million cubic meters less groundwater could be stored. The total permanent loss of storage capacity was estimated at over 9 billion cubic meters.5Journal of Hydrology: Regional Studies. Threat of land subsidence to the groundwater supply capacity of a multi-layer aquifer system That is not water that can be recharged by future rainfall. The physical space that once held the water has been crushed out of existence.
The problem is not limited to China. Machine-learning analysis of the western United States estimated that about 2 cubic kilometers of groundwater storage was lost per year from 2015 to 2016 due to pumping-induced compaction of sediments.6Water Resources Research. Groundwater Storage Loss Associated With Land Subsidence in Western United States Mapped Using Machine Learning In Iran, a satellite survey covering 2014 to 2020 found that roughly 56,000 square kilometers of the country, about 3.5% of its total area, was actively subsiding. Some locations on Iran’s central plateau were sinking at rates exceeding 35 centimeters per year, with an estimated 1.7 billion cubic meters of groundwater depleted annually from confined aquifers. The long-term permanent compaction in most of these aquifers was roughly ten times larger than their seasonal elastic (recoverable) response, underscoring that the damage is largely irreversible.7PubMed Central. Uncovering the impacts of depleting aquifers: A remote sensing analysis of land subsidence in Iran
This form of undermining is quietly devastating. Buildings crack, roads buckle, pipelines snap, and the aquifer itself becomes less capable of storing the very resource it was being tapped for. It is a feedback loop where the act of drawing water destroys the container that held it.
Thawing Permafrost and the Foundations It Takes With It
Across the Arctic and subarctic, a different kind of ground loss is accelerating. Permafrost, soil that has remained frozen for at least two consecutive years and often for millennia, is thawing as global temperatures rise. When it thaws, the ice that bonded soil particles together melts into water, and the ground softens, shifts, and often slumps. Roads built on permafrost develop cracks and waves. Pipelines tilt. Building foundations that were once anchored in rock-hard frozen ground begin to settle unevenly. A comprehensive review of permafrost degradation highlighted the serious and growing threat this poses to roads, pipelines, foundations, and other infrastructure, with particular focus on the risk of soil weakening and foundation instability caused by thawing.8AI in Civil Engineering. Machine learning-based prediction of permafrost degradation and its implications on geotechnical infrastructure: a comprehensive review
What makes permafrost undermining different from the other examples is its sheer geographic scale. Permafrost underlies roughly a quarter of the Northern Hemisphere’s land surface. Communities, transportation networks, and energy infrastructure spanning Russia, Canada, Alaska, and Scandinavia were built on the assumption that the ground beneath them would stay frozen. That assumption is becoming less reliable with each passing decade. Unlike coastal erosion, which is localized, or groundwater depletion, which is concentrated around pumping centers, permafrost thaw affects entire regions and has no engineering fix that can be applied at continental scale.
Animals That Undermine Flood Defenses
Not all undermining is driven by water or temperature. In many river systems, the integrity of levees and earthen dams is quietly compromised by burrowing mammals. Badgers, foxes, nutria, porcupines, and other animals dig dens into levee embankments, creating networks of tunnels that weaken the structure from within. During a flood, water can penetrate these burrows, dramatically shortening the seepage path through the levee and increasing the likelihood of internal erosion and collapse.
Surveys designed to locate animal dens within levees have confirmed that the threat is real but difficult to quantify in advance, because the dens are hidden from view and their geometry is unpredictable.9Journal of Flood Risk Management. Non‐invasive surveys to assess animal burrows as potential causes of levee instability Probabilistic modeling has gone further, showing that mammal dens located near the crest of a levee, where water pressure during a flood is highest, have a significant impact on the levee’s failure probability. The modeled increase in failure risk was consistent with actual levee failures observed in the study area.10Water Resources Research. Failure Probability Analysis of Levees Affected by Mammal Bioerosion
Flood managers call this bioerosion, and it is one of the trickier maintenance problems in levee management. You can inspect the surface of a levee and see nothing wrong while an animal has hollowed out a passage that turns a minor overtopping event into a full breach. Some districts use ground-penetrating radar or electrical resistivity surveys to locate burrows. Others try trapping and relocation programs. But as long as levees are made of soil and animals need shelter, the contest continues.
Ice Shelves Melted From Underneath
At the other end of the temperature spectrum, some of Earth’s largest structures are being undermined by warm ocean water eating at them from below. Floating ice shelves, the seaward extensions of glaciers that rest on the ocean surface, act as buttresses that slow the flow of inland ice toward the sea. When warm water circulates beneath the shelf, it melts the ice from the underside, thinning and weakening the shelf from a direction that satellites cannot easily observe.
Research on Greenland’s Petermann Glacier has shown that intensified meltwater discharge beneath the ice shelf amplifies basal melting in the deepest regions near where the glacier meets the bedrock, a zone called the grounding line. These deeper regions are considered dynamically critical: if they thin enough, the buttressing effect weakens and the inland ice behind them could accelerate its flow into the ocean.11Nature Communications. Enhanced subglacial discharge amplifies Petermann Ice Shelf melting when ocean thermal forcing saturates The concern is that this is a threshold process. The ice shelf looks intact from above, but once the base has been thinned past a critical point, the loss of the deep ice triggers an acceleration that is difficult to reverse. The language researchers use about this, “unopposed acceleration of the inland ice,” is a polite way of describing a very large amount of ice sliding into the sea.
This oceanic undermining of ice shelves is one of the biggest wild cards in projections of future sea-level rise. Surface melting gets more public attention because it is visible, but basal melting can be even more consequential because it strikes at the structural anchor points that hold ice sheets in place.
The Psychological Undermining Effect
The word “undermining” has a second life in behavioral psychology, where it names a phenomenon that puzzled researchers for decades: the observation that paying someone to do something they already enjoy can make them enjoy it less. This is the undermining effect, and it runs directly counter to the common-sense expectation that adding a reward should always increase motivation.
The classic demonstration involves giving people a task they find inherently interesting, like solving puzzles, and then rewarding some of them with money for their performance. Afterward, when left free to continue the task with no reward on the table, the paid participants tend to spend less time on it than those who were never paid. A neuroimaging study confirmed this behavioral pattern and identified the brain regions involved: activity in the anterior striatum and prefrontal cortex declined along with the drop in voluntary engagement, suggesting that the brain’s valuation system integrates the external reward and the internal sense of enjoyment in a way that can reduce the net motivation when the reward is removed.12PubMed Central. Neural basis of the undermining effect of monetary reward on intrinsic motivation
The existence of the undermining effect was debated for years. Some researchers argued that the negative impact of rewards on intrinsic motivation was overstated or limited to narrow laboratory conditions. But a meta-analysis settled the matter for most of the field, finding that tangible rewards do produce a substantial undermining effect and providing strong support for cognitive evaluation theory, the framework that predicts when and why external incentives backfire.13Review of Educational Research. Extrinsic Rewards and Intrinsic Motivation in Education: Reconsidered Once Again The nuance is important, though: not all rewards undermine. Verbal praise tends to enhance motivation. Unexpected rewards cause less harm than expected ones. And rewards for tasks that a person already finds boring do not produce the effect, because there is no intrinsic motivation to displace. The undermining effect specifically targets situations where you take something a person does for its own sake and reframe it as something they do for a payoff.
The practical implications ripple into education, workplace management, and parenting. Sticker charts for a child who already loves reading, performance bonuses for employees who are passionate about their work, gamification points layered onto activities that were already engaging: all of these carry a risk that the reward becomes the reason, and when the reward disappears, so does the behavior. The undermining effect does not mean you should never incentivize anything. It means you should think carefully about whether the person is already motivated before you add an external carrot, because you might be replacing a durable internal drive with a fragile external one.
Engineering Against Undermining
Given the range of physical processes that can hollow out or weaken ground from below, engineering countermeasures against undermining are as varied as the threats themselves. For soil prone to piping or settlement, one widely used technique is jet grouting, in which a high-pressure jet of cement slurry is injected into the ground to create columns of soil-cement that strengthen the soil matrix and resist erosion. A case study of foundation improvement using jet grouting found that the average settlement dropped from about 186 millimeters before treatment to roughly 68 millimeters afterward, a reduction of more than 60%.14E3S Web of Conferences. Excavation Support and Foundation Ground Improvement Using Jet Grouting Method – A Case Study
Other approaches target the water rather than the soil. Dewatering systems lower the water table around an excavation or structure to reduce the hydraulic forces that drive piping. Drainage blankets and relief wells installed at the toe of a dam or levee give seepage water a controlled path to exit, reducing the pressure that would otherwise force its way through weak zones. For coastal cliffs, armoring the base with rock revetments or seawalls can slow wave-cut notch formation, though these structures come with their own problems, including accelerating erosion in adjacent unprotected areas.
Where groundwater depletion has caused subsidence, the engineering challenge is different because the damage is often permanent. You cannot un-compact an aquifer that has been crushed. The most effective intervention is prevention: managed aquifer recharge programs that inject treated water back into the ground to maintain pressure and prevent further compaction. In some regions, this has slowed or halted subsidence, but it cannot restore the storage capacity that has already been lost. For permafrost, experimental techniques include thermosyphons, passive cooling devices driven into the ground to keep it frozen, but these are point solutions that work for individual buildings or pipeline segments, not entire landscapes.
The common thread in all of these countermeasures is that they are most effective when applied before undermining has reached an advanced stage. Once a void has formed, a cliff has been notched through, or an aquifer has been irreversibly compacted, the options narrow considerably. Undermining, in nearly every domain where the word applies, rewards early detection and penalizes delay.
Siege Mining and the Original Meaning
Before undermining was a geological term or a psychological concept, it was a military one. In medieval and ancient siege warfare, “mining” or “undermining” meant digging a tunnel beneath an enemy’s fortification wall, propping it up with wooden timbers, then setting the timbers on fire. When the supports burned through, the tunnel collapsed and the wall above it came down with it, creating a breach that attacking troops could pour through. The tactic was used for centuries across cultures and continents, from Roman sieges in the Middle East to European castle warfare in the medieval period.
Archaeological evidence from the ancient city of Dura-Europos in Syria provides a striking example. Excavations there revealed siege tunnels from a Sasanian assault in the third century CE, including evidence that the defenders dug counter-mines to intercept the attackers underground. The conflict that played out beneath those walls, tunnel against tunnel in cramped darkness, was the literal original meaning of “undermining”: removing the support beneath something to bring it down. Every modern usage, whether describing waves eating a cliff, groundwater collapsing a landscape, or a paycheck eroding a person’s love of their work, traces its metaphorical DNA back to that tunnel beneath the wall.