Earth Fissures Ground Cracks Explained: Causes, Types, Hazards and Warning Signs

What Is an Earth Fissure?

An earth fissure is a long, narrow fracture that opens at the ground
surface when shallow soil, sediment or weak rock is placed under tension or displaced.
Fissures may be only a few centimeters wide when they begin but can extend for hundreds
of meters or several kilometers.

Many fissures form where one part of the ground sinks faster than another. The difference
in movement stretches the sediment between the two areas until it fractures.

The initial opening may be small and difficult to see. Once water enters, however, erosion
can remove soil from the crack walls and transport it underground. A narrow fracture may
then develop into a deep trench, gully or irregular collapse zone.

Earth fissures are generally associated with unconsolidated or weakly cemented sediment,
but fractures can also form in rock during earthquakes, volcanic unrest, slope movement,
mine collapse or thawing permafrost.

Typical Characteristics

• Long, narrow and commonly linear or gently curved.
• May appear as one crack or a zone of parallel fractures.
• Often develops near the margin of a subsiding basin.
• Can intersect roads, canals, fields and building foundations.
• May enlarge dramatically after rain, flooding or irrigation.
• Can be shallow at one location and unexpectedly deep nearby.
• May reopen after being filled if the underlying movement continues.

How Do Earth Fissures Form?

Ground cracks form when stress exceeds the strength of the surface material. The exact
source of stress varies, but most fissures involve one of four broad mechanisms:

1. Tension: the ground is pulled apart because adjacent areas move at
   different rates.
2. Settlement: weak sediment compacts, collapses or loses support.
3. Displacement: faulting, landsliding or volcanic deformation shifts
   the ground.
4. Shrinkage: clay, peat or frozen ground loses water or ice and decreases
   in volume.

Typical Subsidence-Fissure Development

1. Groundwater or another subsurface fluid is removed.
2. Compressible sediment layers compact.
3. The land surface sinks unevenly.
4. Tension accumulates between faster- and slower-sinking areas.
5. A narrow fracture opens in the shallow sediment.
6. Rainwater enters and erodes the crack.
7. The opening becomes wider, deeper and more hazardous.

The spectacular opening seen in photographs is therefore often the final stage of a
process that began invisibly underground months or years earlier.

Earth Fissure vs Ground Crack: Is There a Difference?

Ground crack is a broad descriptive term for almost any fracture visible
at the surface. It can refer to tiny drought cracks, damaged pavement, frost cracks,
earthquake ruptures or large subsidence fissures.

Earth fissure is usually used for a more substantial, persistent and
elongated ground fracture linked to geological or hydrological movement.

Earth Fissure vs Sinkhole

Earth fissures and sinkholes are both forms of ground failure, but their geometry and
formation mechanisms are usually different.

The distinction is not always absolute. Cracks can form around the edge of a developing
sinkhole, and a fissure enlarged by underground erosion can eventually develop localized
collapses.

Explore the dedicated guide:

Sinkholes Explained: Dolines, Karst and Ground Collapse
.

Earth Fissure vs Earthquake Fault Rupture

A long ground crack is not automatically an earthquake fault. Most earth fissures form
in shallow sediment and do not represent movement along a deep tectonic fault.

Signs of a Subsidence Fissure

• Occurs in a groundwater basin or area of known land subsidence.
• May follow the edge of buried bedrock.
• Commonly grows through erosion after rain.
• May reopen repeatedly without felt earthquakes.
• Often has little initial offset between its two sides.

Signs of Possible Earthquake Surface Rupture

• Appears immediately during or after a significant earthquake.
• Follows a mapped or newly identified fault trace.
• Shows clear vertical, horizontal or oblique displacement.
• May cross roads, stream channels, fences and geological layers with consistent offset.
• Is documented by geological or seismic agencies.

Strong earthquake shaking can also cause non-fault cracks through liquefaction, lateral
spreading, landslides, embankment settlement and ground compaction. A crack appearing
after an earthquake is therefore not automatically the fault rupture itself.

Main Types of Earth Fissures and Ground Cracks

Ground cracks can be classified according to their dominant formation process.

Subsidence-Related Earth Fissures

Subsidence fissures are among the largest and most hazardous earth cracks found in dry
sedimentary basins. They form where the ground is sinking unevenly rather than uniformly.

If an entire basin lowered at exactly the same rate, relatively little cracking might
occur. In reality, sediment thickness, groundwater withdrawal, bedrock depth and soil
properties vary from place to place.

One part of a basin may sink rapidly while a neighboring area remains comparatively stable.
The transition zone is stretched, producing tension fractures.

Why Fissures Often Form Near Basin Margins

Thick basin sediment can compact substantially, while shallow bedrock near the basin edge
barely compresses. The strongest difference in vertical movement may therefore occur above
buried bedrock slopes or ridges.

Fissures can also form:

• Along buried faults separating sediments of different thickness.
• Near concentrated groundwater-pumping centers.
• Where clay-rich layers abruptly thin or disappear.
• Along boundaries between natural sediment and artificial fill.
• Where surface-water drainage repeatedly enters existing cracks.

Read the full companion guide:

Land Subsidence Explained
.

Groundwater Pumping, Aquifer Compaction and Earth Fissures

Groundwater pumping does not usually open a crack by simply removing water from a hollow
chamber. Aquifers are generally made of sediment or fractured rock containing water in
pore spaces.

When groundwater levels fall, pore-water pressure decreases. More of the overlying weight
is transferred to the sediment framework. Fine-grained clay and silt layers may compact,
causing the land surface to sink.

From Pumping to Fissure Formation

1. Wells remove groundwater faster than natural recharge replaces it.
2. Groundwater levels and pore pressure decline.
3. Compressible sediment layers become thinner.
4. The land surface sinks unevenly.
5. Tension develops between areas with different subsidence rates.
6. Shallow sediment fractures and opens.
7. Rainfall erodes and enlarges the fissure.

The fissure is therefore a surface symptom of a larger groundwater and subsidence problem.
Filling the visible crack does not stop the underlying aquifer compaction.

Desiccation Cracks and Drought Shrinkage

Desiccation cracks form when wet, clay-rich soil dries and contracts. Because the surface
cannot shrink uniformly, it breaks into a network of polygonal blocks.

Typical Desiccation-Crack Characteristics

• Polygonal or honeycomb-shaped pattern.
• Common on dry lake beds, mudflats, reservoirs and agricultural soil.
• Usually shallow compared with major subsidence fissures.
• May close or partially fill when the soil becomes wet again.
• Can reopen during repeated wet-dry cycles.

Shrinkage cracks can also form beneath foundations and roads. Expansive clay swells when
wet and shrinks when dry, producing repeated movement that damages structures.

Very large drought cracks may look alarming, but their polygonal geometry and widespread
shallow distribution often distinguish them from fault ruptures or deep earth fissures.

Collapse-Related Fissures

Cracks often form before, during or after the failure of underground support. As the ground
begins to sag toward a void, the surface is bent and stretched.

Possible Underground Causes

• Natural karst cavities.
• Abandoned mines.
• Old tunnels and shafts.
• Broken sewer or water pipes.
• Washed-out road fill.
• Buried channels or weak sediment lenses.
• Underground peat or coal fires.
• Decaying underground structures.

Collapse-related cracks may curve around a developing depression. Concentric fractures,
sagging pavement and tilting walls can indicate that a larger failure zone exists beneath
the visible surface.

Do not approach the edge of an unexplained collapse crack. The apparent boundary may be
supported by only a thin bridge of soil.

Piping, Tunneling and Underground Erosion

Soil piping occurs when moving water removes fine particles from beneath
the ground, creating small tunnels or enlarged flow paths.

Piping may begin around:

• Leaking water mains or sewers.
• Canals and irrigation ditches.
• Dams, levees and embankments.
• Natural springs and seepage zones.
• Animal burrows.
• Cracks produced by subsidence or drying.

As material is removed, the roof of the underground channel can collapse. Surface cracks
may connect the collapse points and eventually develop into a continuous gully.

Why Piping Is Easily Misidentified

A piping feature can resemble a tectonic fissure because it may be long, narrow and deep.
Evidence of flowing water, sediment discharge, leaking infrastructure or repeated enlargement
after storms often points toward erosion rather than fault movement.

Mining, Tunneling and Excavation-Related Ground Cracks

Underground extraction removes material that once supported the ground above. Roof collapse,
pillar failure or gradual deformation can migrate upward and fracture the surface.

Mining-Related Crack Patterns

• Parallel tension cracks along the edge of a subsidence trough.
• Circular or irregular cracks around a crown hole.
• Steps and offsets above collapsing mine workings.
• Cracked roads and foundations above abandoned entries.
• Delayed cracking years or decades after mine closure.

Surface maps may not show every abandoned shaft or working. Historic mines can therefore
remain hazardous long after their entrances have disappeared.

Open-pit excavation can also destabilize nearby slopes, while tunneling and dewatering can
cause settlement in urban areas.

Landslide Tension Cracks and Slope-Movement Fractures

A curved crack near the top of a slope can be an early sign that a landslide mass is pulling
away from stable ground.

These cracks commonly form near the head scarp of a slide. They may widen
as the moving block travels downslope.

Possible Landslide Warning Signs

• Curved cracks running roughly parallel to a slope edge.
• Fresh scarps or steps in the ground.
• Leaning trees, fences or utility poles.
• Bulging soil near the base of a slope.
• Doors and windows suddenly becoming difficult to close.
• New springs, wet patches or disrupted drainage.

Water entering an open tension crack can increase pore pressure and add weight to the
moving material, potentially accelerating slope failure.

Explore:

Landslides and Mudslides Explained
.

Earthquake Surface Rupture

Earthquake surface rupture occurs when displacement on a fault reaches the ground surface.
The rupture may produce a crack, scarp, pressure ridge or zone of broken and offset ground.

Surface rupture is most likely during shallow earthquakes on faults capable of producing
significant displacement. Not every earthquake ruptures the surface.

Types of Surface Displacement

• Strike-slip offset: the two sides move horizontally past one another.
• Normal-fault displacement: one side moves downward relative to the other.
• Reverse or thrust displacement: one side is pushed upward over the other.
• Oblique displacement: horizontal and vertical movement occur together.

Secondary Earthquake Cracks

Earthquakes also create cracks away from the actual fault through:

• Liquefaction.
• Lateral spreading.
• Landslides and rockfalls.
• Settlement of artificial fill.
• Failure of embankments and levees.
• Compaction of loose sediment.

A post-earthquake crack must therefore be mapped and investigated before it can be described
as confirmed surface fault rupture.

Volcanic Fissures and Magma-Driven Ground Cracking

Volcanic fissures form when magma intrudes into the crust and pushes surrounding rock apart.
A sheet-like magma intrusion known as a dike can produce surface cracking,
uplift and horizontal extension.

Some fissures become eruptive vents, producing aligned lava fountains and lava flows.
Others open without erupting because the magma remains underground.

Possible Signs of Magma-Driven Fissuring

• Earthquake swarms.
• Rapid ground deformation.
• New fractures aligned across volcanic terrain.
• Changes in gas emissions.
• Elevated ground temperatures.
• Steam release or volcanic eruption along the fracture system.

Volcanic fissures should not be confused with ordinary drought cracks or subsidence fissures.
They occur within a broader pattern of volcanic unrest that monitoring agencies evaluate
using seismic, deformation, gas and thermal observations.

Permafrost, Thermokarst and Freeze-Thaw Ground Cracks

Frozen ground develops several distinctive types of cracks. Very cold conditions can cause
thermal contraction, while seasonal thaw or long-term permafrost degradation can make the
surface settle unevenly.

Ice-Wedge Polygons

Repeated thermal contraction creates polygonal cracks in permafrost. Meltwater enters and
freezes, gradually building wedges of ground ice.

Thermokarst Cracks

When ice-rich permafrost thaws, the ground loses volume and strength. Irregular cracks,
depressions and collapsing terrain can develop around thaw lakes, roads and buildings.

Frost Cracks

Rapid cooling can fracture frozen soil or rock. These features may produce sudden noises
but are generally unrelated to tectonic fault rupture.

Related:

Permafrost Collapse and Thermokarst Explained
.

Human Activities That Trigger or Worsen Ground Cracks

Many earth fissures are natural in the sense that they follow geological and hydrological
processes, yet human activity can initiate or greatly accelerate those processes.

Groundwater Withdrawal

Pumping lowers pore pressure and compacts aquifer sediments, producing differential
subsidence and tension cracking.

Mining and Tunneling

Excavation creates underground voids and redistributes stress. Collapse can fracture the
surface long after mining ends.

Construction and Artificial Fill

Poorly compacted fill settles unevenly. Heavy buildings, road embankments and excavation
can create additional stress.

Broken Pipes and Altered Drainage

Leaking water can wash soil away underground, while stormwater concentrated into an existing
crack can transform it into a large erosional trench.

Peat and Wetland Drainage

Organic soil shrinks, oxidizes and loses elevation when drained. Uneven settlement can
fracture roads, levees and foundations.

Oil, Gas and Geothermal Extraction

Removing underground fluids can compact reservoirs and surrounding sediment. Fluid injection
can also alter underground pressure and, in some settings, trigger seismicity.

Learn more:

Induced Seismicity and Man-Made Earthquakes Explained
.

Why Rain and Runoff Make Earth Fissures Larger

Rain does not necessarily create the original fracture, but it often transforms a small
crack into a dangerous feature.

Fissure Enlargement Process

1. Rainwater flows toward the low opening.
2. Water enters the crack and saturates its walls.
3. Fine particles are detached and transported downward.
4. The walls lose support and collapse inward.
5. Runoff becomes concentrated in the enlarged channel.
6. Additional erosion deepens and widens the fissure.

In dry regions, a fissure may remain almost unnoticed until a powerful storm funnels large
volumes of water into it. The resulting erosion can create the impression that the ground
suddenly opened overnight.

Why Filling a Fissure May Fail

Dumping loose soil into a crack does not correct active subsidence or underground erosion.
The fill may wash away, settle or conceal a remaining void.

Effective repair requires identifying the cause, redirecting water safely and determining
whether deeper stabilization is necessary.

Where Do Earth Fissures Occur?

Ground cracks can occur almost anywhere, but major fissure systems are especially common
in environments where weak sediment, strong groundwater demand and uneven subsidence overlap.

Arid and Semiarid Groundwater Basins

Dry basins often depend heavily on groundwater for cities and agriculture. Thick sediment
sequences containing compressible clay can subside as water levels decline.

Agricultural Valleys

Intensive irrigation pumping can produce large subsidence bowls and earth fissures,
particularly during prolonged drought.

Rapidly Growing Cities

Urban groundwater demand, heavy construction, leaking infrastructure and development over
soft sediment can produce complex patterns of settlement.

Mining Districts

Active and abandoned mines can produce cracks, subsidence troughs and localized collapse.

Karst Landscapes

Limestone, gypsum and salt terrain may develop fractures around subsiding or collapsing
cavities.

Active Fault Zones

Earthquake surface rupture and fault creep can fracture and offset the ground along active
faults.

Volcanic Rift Zones

Magma intrusion and crustal extension can produce long fracture systems and eruptive fissures.

Permafrost Regions

Thermal contraction and thaw settlement create polygonal cracks and irregular collapse zones.

Warning Signs of Earth Fissures and Ground Instability

Some fissures appear with little warning, while others are preceded by subtle deformation.

Possible Warning Signs

• New linear cracks in soil, pavement or concrete.
• Cracks that lengthen or widen after storms.
• Recurring cracks that reopen after repair.
• Sagging road surfaces or shallow depressions.
• Unexpected ponding or changes in drainage.
• Walls, floors or foundations developing new fractures.
• Utility poles, trees or fences beginning to lean.
• Pipelines or water mains repeatedly breaking.
• New steps or offsets across roads and fields.
• Fresh curved cracks near the top of a slope.
• Sand, muddy water or sediment emerging from the ground.
• Unusual noises associated with active collapse.

None of these signs identifies the cause by itself. Expansive soil, poor construction,
landsliding, leaking pipes and ordinary settlement can produce similar damage.

Earth Fissure Hazards

An earth fissure is more than a line in the ground. It may indicate active deformation,
unstable sediment or a hidden underground void.

Unstable Edges

Crack walls can collapse without warning, especially after rain or when someone approaches
the edge.

Hidden Depth

Loose soil and debris may conceal a much deeper opening. Some fissures connect to underground
erosion channels or cavities.

Vehicle Accidents

Cracks crossing roads can damage tires, axles and foundations or cause vehicles to lose control.

Damage to Buildings

Differential movement can fracture slabs, walls and foundations. Repairing the visible crack
without stabilizing the ground may provide only temporary relief.

Utility Failure

Water mains, gas pipes, sewers, electrical conduits and communication lines can break or
deform where the ground separates.

Flood and Drainage Problems

Fissures redirect runoff underground, undermine canals and levees, and may create new pathways
for contamination to reach aquifers.

Livestock and Wildlife Hazards

Animals can fall into narrow openings hidden by vegetation or loose sediment.

What to Do When a Ground Crack Appears

Treat an unexplained ground opening as a genuine hazard until its cause and stability are known.

Immediate Safety Steps

• Stay away from the edge. The visible boundary may be unsupported.
• Keep children, pets and livestock away.
• Do not drive across the crack.
• Do not enter the opening. It may contain unstable walls, water or gases.
• Do not pour water into it. Water can accelerate erosion and collapse.
• Avoid placing heavy equipment nearby.

Document the Feature Safely

• Photograph it from stable ground.
• Record the date, time and approximate location.
• Note whether it appeared after rain, drought, construction or an earthquake.
• Record whether the crack is widening, lengthening or producing water or sediment.

Report It

Contact local emergency services, public works, road authorities, the property owner or a
geological agency when a fissure threatens people, buildings, utilities or transportation.

Seek Professional Investigation

Depending on the setting, evaluation may require an engineering geologist, geotechnical
engineer, hydrogeologist, mining specialist or structural engineer.

How Scientists Investigate Earth Fissures

A reliable diagnosis combines surface observations with information about the underground
geology, groundwater system and recent activity.

Field Mapping

Researchers map the crack’s length, direction, width, depth, branching pattern and
relationship to roads, slopes, faults and drainage channels.

Surveying and GPS

Repeated elevation measurements show whether the surrounding land is sinking, tilting or
moving horizontally.

InSAR Satellite Monitoring

Radar satellite data can reveal broad subsidence bowls and deformation patterns that are
invisible from the ground.

Groundwater Measurements

Well records help determine whether water-level decline and aquifer compaction correspond
with fissure development.

Geophysical Surveys

Ground-penetrating radar, electrical resistivity, seismic methods and microgravity can help
identify voids, weak layers and disturbed sediment.

Drilling and Soil Testing

Boreholes reveal subsurface layers, groundwater conditions, collapsible soils and buried
mine workings.

Historic Maps and Records

Old mine plans, drainage maps, aerial photographs and construction records may reveal a
previously unknown cause.

Can Earth Fissures Be Prevented or Repaired?

Some fissures can be prevented or stabilized, but only if the underlying cause is addressed.

Manage Groundwater Pumping

• Reduce excessive extraction.
• Maintain groundwater levels above critical compaction thresholds.
• Increase managed aquifer recharge where appropriate.
• Distribute pumping more evenly across a basin.
• Improve irrigation and water-use efficiency.

Control Surface Water

• Redirect runoff away from open fissures.
• Repair leaking pipes and canals.
• Avoid concentrating stormwater into unstable ground.
• Stabilize drainage channels before filling a crack.

Investigate Underground Voids

• Map abandoned mines and tunnels.
• Stabilize or backfill cavities when technically appropriate.
• Restrict development over known unstable workings.

Use Appropriate Engineering Solutions

Depending on the cause, remediation may involve excavation, engineered fill, grouting,
drainage control, flexible utility connections, deep foundations or relocation.

Why Simple Filling Often Fails

Filling the surface opening may temporarily remove the visible hazard but will not stop
active subsidence, fault movement, landsliding or underground erosion.

Common Myths About Earth Fissures and Ground Cracks

Myth 1: Every Long Crack Is an Earthquake Fault

False. Subsidence, drought, landslides, mining and erosion produce many more surface cracks
than confirmed earthquake rupture.

Myth 2: The Planet Is Splitting Apart

Most fissures reflect local or regional ground movement, not a crack extending deep through
the planet.

Myth 3: A Crack That Appeared Overnight Formed Instantly

Not necessarily. Slow underground deformation may precede sudden visible erosion or collapse.

Myth 4: Pouring Water into a Fissure Helps Close It

False. Water can erode the walls, wash soil underground and make the opening larger.

Myth 5: Filling the Crack Solves the Problem

Surface filling does not stop ongoing subsidence, underground erosion or fault movement.

Myth 6: Small Cracks Are Always Harmless

A small opening can connect to a deeper fracture or void. Its risk depends on the underlying
process, not only its surface width.

Myth 7: Cracks After an Earthquake Must Be the Fault

Earthquake shaking also causes landslides, liquefaction, settlement and lateral spreading.