Permafrost Collapse and Thermokarst in 60 Seconds

What Is Permafrost?

Permafrost is ground—soil, sediment, rock and any contained
organic material or ice—that remains at or below 0°C for at least two
consecutive years.

Permafrost is defined by temperature, not by appearance. It does not have to be
permanently covered by snow or surface ice. Tundra vegetation, forests, wetlands,
roads and buildings can all lie above permafrost.

Permafrost May Contain:

• Mineral soil.
• Frozen peat and organic matter.
• Bedrock.
• Frozen sand, silt, clay and gravel.
• Pore ice between sediment grains.
• Ice lenses.
• Ice wedges.
• Buried glacier ice.
• Large bodies of massive ground ice.

The amount, type and distribution of ice determine how strongly the ground
responds when thaw occurs.

Continuous and Discontinuous Permafrost

Permafrost distribution is commonly divided into broad zones:

• Continuous permafrost: Frozen ground underlies nearly all of
  the landscape.
• Discontinuous permafrost: Frozen and unfrozen ground occur
  together across the region.
• Sporadic permafrost: Permafrost occurs in scattered patches.
• Isolated permafrost: Small frozen bodies survive only in
  favorable local settings.

Permafrost also occurs in high mountains outside polar regions, where elevation,
slope direction, snow cover and rock type control ground temperature.

What Is Thermokarst?

Thermokarst is the process by which thawing ice-rich permafrost
or melting massive ground ice produces characteristic subsidence, depressions,
irregular terrain, ponds, lakes and slope failures.

The term is also used for the landscapes and landforms created by that process.

Why Is It Called Thermokarst?

Thermokarst terrain can resemble limestone karst because both may contain pits,
depressions, lakes and disrupted drainage.

However:

• Karst develops mainly through dissolution of soluble rock.
• Thermokarst develops mainly through melting ground ice and
  thaw-induced subsidence.

Active Thermokarst

Active thermokarst describes terrain where thaw-driven landforms are currently
developing or expanding.

Relict Thermokarst

Some depressions and drained lake basins remain visible after the active thaw
process has slowed or stopped. These older features preserve evidence of past
permafrost degradation.

Why Ground Ice Controls Permafrost Collapse

Frozen ground does not always collapse when it thaws. The outcome depends
largely on how much ice it contains relative to the volume of soil or sediment.

Pore Ice

Pore ice fills spaces between sediment grains. If the amount of ice does not
exceed the normal pore space, thaw may weaken the ground without producing
dramatic settlement.

Excess Ground Ice

Excess ice is ice exceeding the natural pore volume of the
unfrozen sediment. When it melts, the remaining mineral and organic material
cannot occupy the same volume, so the ground surface sinks.

Ice Lenses

Ice lenses are layers or bodies of segregated ice that form as water migrates
toward a freezing front. Thick lenses can produce substantial settlement when
thawed.

Ice Wedges

Ice wedges form when extreme winter cooling creates contraction cracks that
repeatedly fill with snowmelt and refreeze. Over centuries, wedge-shaped masses
of ice grow beneath polygonal ground.

Massive Ice

Massive ground ice includes large, nearly pure bodies of buried ice. Some formed
through repeated ice segregation, while others may represent buried glacier ice.

Landscapes containing massive ice can undergo deep, rapid and highly irregular
collapse.

The Active Layer and Permafrost Table

The active layer is the surface layer above permafrost that
freezes in winter and thaws during summer.

Beneath it lies the permafrost table, the upper boundary of
perennially frozen ground.

What Controls Active-Layer Thickness?

• Summer air temperature.
• Length of the thaw season.
• Snow depth.
• Vegetation cover.
• Soil moisture.
• Peat thickness.
• Wildfire history.
• Surface-water coverage.
• Ground texture and ice content.
• Slope direction and elevation.

Why Active-Layer Deepening Matters

If summer thaw penetrates more deeply, previously frozen sediment and ground ice
become part of the seasonal thaw zone.

This can:

• Increase soil settlement.
• Mobilize water and sediment.
• Destabilize slopes.
• Expose frozen organic matter to decomposition.
• Damage shallow foundations and buried utilities.
• Initiate thermokarst depressions.

Permafrost Warming vs Permafrost Thaw

Permafrost warming and permafrost thaw are related but not identical.

Permafrost can warm for years before visible collapse begins. Once thaw reaches
ice-rich layers, deformation may accelerate abruptly.

How Permafrost Collapse Begins

Thermokarst commonly begins when the surface energy balance changes and more
heat reaches ice-rich frozen ground.

Common Triggers

• Unusually warm summers.
• Longer thaw seasons.
• Persistent surface-water ponding.
• Wildfires removing vegetation and insulating peat.
• Riverbank or coastal erosion exposing frozen sediment.
• Heavy rainfall saturating the active layer.
• Snowdrifts insulating the ground during winter.
• Road construction altering drainage.
• Buildings transferring heat downward.
• Removal of surface vegetation.
• Vehicle traffic disturbing tundra soils.

A Typical Thermokarst Sequence

1. The ground surface becomes warmer or wetter.
2. The active layer deepens.
3. Ground ice begins to melt.
4. The soil loses volume and structural strength.
5. The surface settles unevenly.
6. Water accumulates in the depression.
7. The water absorbs and transfers additional heat.
8. More permafrost thaws beneath and around the depression.
9. The feature expands into a pond, lake, trough or slump.

This sequence is not universal, but it illustrates why thermokarst can develop
through self-reinforcing feedbacks.

Main Thermokarst Landforms

Flagship Arctic Case Study

Yamal Craters: Explosive Permafrost Failure in the Russian Arctic

Since 2014, enormous circular craters discovered on Russia’s
Yamal and Gydan Peninsulas have become some of the most
spectacular examples of sudden Arctic ground failure ever documented.

Their steep walls, great depth and abrupt appearance initially triggered
speculation about meteorite impacts, industrial accidents and other unusual
causes. Scientific investigations now indicate that the craters are most
likely produced by explosive gas release beneath frozen ground.

These features are associated with permafrost, ground ice, subsurface gas
accumulation and weakening frozen sediment. However, they are
not ordinary thermokarst depressions.

How the Yamal Craters May Form

Although the exact sequence may differ between sites, the leading formation
model involves several stages:

1. Ice-rich permafrost and frozen sediment overlie gas-bearing layers or
   localized pockets of methane-rich gas.
2. Changes in ground temperature, pressure and water movement allow gas to
   accumulate beneath a relatively impermeable frozen cap.
3. The surface may begin to rise, forming a mound or pingo-like hill.
4. Gas pressure continues increasing while the frozen cap weakens.
5. The cap fails catastrophically.
6. Frozen soil, peat, sediment and ice are thrown outward during the explosion.
7. A deep, steep-sided cylindrical crater remains.
8. Snowmelt, rainfall and groundwater gradually fill the crater, producing a
   circular lake.

The Possible Role of Pingos

Some Yamal craters appear to develop beneath raised mounds resembling
pingos. A pingo is an ice-cored hill created when groundwater
freezes and expands beneath the surface.

Satellite observations have shown that certain crater sites were preceded by
years of gradual surface uplift. This suggests that pressure may build beneath
the frozen ground before the final rupture.

However, not every pingo explodes, and researchers continue to investigate
whether all Yamal craters follow the same formation pathway.

What Happens After the Explosion?

Fresh Yamal craters may have nearly vertical frozen walls, exposed ground ice,
debris scattered around the rim and a water-filled bottom.

Over time:

• The walls thaw and retreat.
• Frozen sediment collapses into the opening.
• The crater widens.
• Rain, snowmelt and groundwater increase the water level.
• The original crater gradually becomes a rounded lake.
• Vegetation may eventually obscure evidence of the explosive origin.

This transformation means that older explosion craters may be difficult to
distinguish from ordinary thermokarst lakes after several years or decades.

Are the Yamal Craters Thermokarst?

The answer requires an important distinction.

The initial crater is best described as a
gas-driven explosive permafrost feature, not a conventional
thermokarst depression. Its formation involves catastrophic rupture rather
than slow thaw subsidence.

After the explosion, however, thawing crater walls, melting ground ice,
subsidence and lake expansion may produce secondary
thermokarst processes.

Why the Yamal Craters Matter

The Yamal craters reveal that permafrost landscapes do not always degrade
through slow and predictable subsidence. Under rare conditions, gas pressure
can produce sudden and violent ground rupture.

• They expose hidden gas accumulation beneath frozen terrain.
• They demonstrate that some permafrost failures can occur abruptly.
• They provide evidence of interactions among gas, ground ice and thaw.
• They help scientists study pingo-like uplift and frozen-ground pressure.
• They may represent a localized hazard near Arctic infrastructure.
• They show how explosive craters can later evolve into ordinary-looking lakes.

Are These Craters Becoming More Common?

Only a limited number of confirmed explosive craters have been documented.
Better satellite imagery, drone surveys and Arctic fieldwork have increased
the likelihood that new examples will be detected.

It remains difficult to determine whether the actual frequency of these events
is increasing or whether scientists are simply finding more of them. Long-term
monitoring is still required.

Thaw Subsidence and Uneven Ground

Thaw subsidence is the downward movement of the ground surface
following the melting of ground ice and consolidation of thawed sediment.

Subsidence may be:

• Gradual or sudden.
• Uniform or highly irregular.
• Limited to centimeters or measured in meters.
• Seasonal, episodic or progressive.

Differential Thaw Settlement

Ground ice is rarely distributed evenly. One part of a site may contain thick
ice lenses while a neighboring area contains relatively little ice.

When thaw occurs, different parts of the surface settle by different amounts.
This differential settlement can crack roads, tilt buildings,
distort pipelines and create hummocky terrain.

Why Water Collects in Subsided Ground

Depressions alter local drainage. Rain and snowmelt collect in the low areas,
increasing soil moisture and heat transfer and potentially accelerating further
thaw.

Thaw Pits, Depressions and Collapse Scar Bogs

Small thermokarst features often begin as shallow depressions above melting
ground ice.

Thaw Pits

Thaw pits are localized hollows produced when ice-rich patches melt and the
overlying surface collapses.

They may remain dry, collect seasonal water or merge with neighboring
depressions.

Thermokarst Depressions

Larger depressions can form through continued thaw, coalescence of pits or
collapse above massive ice.

Collapse Scar Bogs

In peatlands, thawing frozen peat plateaus may subside into wet depressions known
as collapse scar bogs.

These features often contain waterlogged vegetation and differ sharply from the
drier elevated frozen peat around them.

Retrogressive Thaw Slumps

A retrogressive thaw slump is a large thaw-driven slope failure
that develops where ice-rich permafrost is exposed and begins melting.

These features commonly contain:

• A steep retreating headwall.
• Exposed ground ice or frozen sediment.
• A muddy, water-saturated slump floor.
• Flowing sediment and meltwater.
• A tongue or fan of displaced material downslope.

Why Are They Called Retrogressive?

The headwall retreats backward into previously undisturbed ground as thaw
continues. The scar therefore expands upslope or inland over time.

How Thaw Slumps Begin

Initial disturbance may come from:

• Riverbank erosion.
• Coastal erosion.
• Lake-shore retreat.
• A small landslide.
• Wildfire disturbance.
• Road cuts and excavation.
• Exceptionally warm or wet summers.

Why Can Thaw Slumps Grow So Large?

Once the insulating surface layer is removed, dark soil and exposed ice absorb
heat. Meltwater destabilizes sediment, while flowing water carries thawed
material away and exposes more frozen ground.

Environmental Effects

• Large sediment pulses into rivers and lakes.
• Release of dissolved minerals and nutrients.
• Increased water cloudiness.
• Burial of vegetation.
• Changes in stream chemistry.
• Expansion of barren ground.

Active-Layer Detachment Slides

An active-layer detachment slide occurs when the seasonally
thawed surface layer separates and slides over still-frozen ground beneath it.

The frozen permafrost acts as a relatively impermeable and mechanically distinct
boundary.

Common Triggers

• Rapid snowmelt.
• Heavy or prolonged rainfall.
• Unusually deep summer thaw.
• Steep slopes.
• Water saturation at the frozen boundary.
• Loss of vegetation after fire or disturbance.

How Are They Different From Thaw Slumps?

Active-layer detachments are generally shallow slides involving the thawed
surface layer. Retrogressive thaw slumps expose and melt deeper ice-rich
permafrost and may remain active for many years.

Thermal Erosion and Thermal Abrasion

Permafrost degradation can be accelerated by moving water.

Thermal Erosion

Thermal erosion occurs when flowing water transfers heat to frozen ground and
physically removes thawed sediment.

It commonly affects:

• Riverbanks.
• Gullies.
• Ice-wedge troughs.
• Lake outlets.
• Drainage channels.

Thermal Abrasion

Thermal abrasion describes the combined action of heat and wave erosion against
ice-rich frozen banks or coastal bluffs.

Waves remove thawed material, exposing fresh permafrost to additional thaw.

Why Water Is So Effective

Water transports heat efficiently and removes the muddy sediment that would
otherwise accumulate and partly insulate frozen ground.

Thermokarst Lakes and Ponds

A thermokarst lake forms when water collects in a depression
created by thawing and subsidence of ice-rich permafrost.

How a Thermokarst Lake Forms

1. A small patch of ground begins to thaw.
2. The surface settles as ground ice melts.
3. Water collects in the depression.
4. The water absorbs solar energy.
5. Heat is transferred downward and sideways.
6. Additional permafrost thaws.
7. The basin deepens and expands.

Are All Arctic Lakes Thermokarst Lakes?

No. Arctic lakes may occupy glacial depressions, river channels, coastal basins,
volcanic craters or other landforms.

A thermokarst origin requires evidence that thaw subsidence contributed
significantly to formation or expansion of the basin.

Taliks Beneath Lakes

A talik is a body of unfrozen ground within or beneath
permafrost.

Deep lakes may remain unfrozen at the bottom during winter, allowing a talik to
develop beneath them. Continued heat transfer through the lake can deepen the
unfrozen zone.

Why Thermokarst Lakes Expand

Thermokarst lakes may enlarge through a combination of shoreline thaw, wave
erosion and subsidence.

Expansion Mechanisms

• Water warms ice-rich shoreline sediment.
• Waves remove thawed material.
• Ice wedges melt around polygon margins.
• Lake-bottom thaw deepens the basin.
• Neighboring ponds merge.
• Drainage channels deliver more water.
• Shoreline thaw slumps retreat into the surrounding terrain.

Positive Feedback

Expansion can expose additional frozen ground to water and wave action, which
promotes further thaw and retreat.

This feedback does not continue indefinitely. Lake growth may slow when the
shoreline reaches ice-poor sediment, bedrock or better-drained terrain.

Why Thermokarst Lakes Drain

Thermokarst lakes do not only expand. They can also drain partially or
completely.

Common Drainage Mechanisms

• Coastal erosion breaches the lake margin.
• A river cuts into the basin.
• Ice-wedge troughs create a drainage channel.
• A lake expands into lower neighboring terrain.
• Permafrost degradation opens subsurface pathways.
• The lake overtops and erodes its outlet.
• Human construction alters drainage.

Sudden vs Gradual Drainage

Some lakes lose water slowly over years. Others drain rapidly when an outlet
channel breaches the basin margin.

What Happens After Drainage?

The exposed lakebed may become:

• A wet meadow.
• A marsh or peatland.
• A network of small ponds.
• A river channel.
• A new site of permafrost growth.
• A source of dust or sediment.

Depending on local climate and drainage, permafrost can sometimes begin
re-forming beneath a drained lake basin.

Drained Thermokarst Lake Basins

Drained thermokarst lake basins are widespread across many Arctic lowlands.
They preserve the outlines of former lakes and record repeated cycles of thaw,
lake formation, expansion and drainage.

How to Recognize a Drained Basin

• A flat or gently sloping basin floor.
• A distinct former shoreline.
• Wetland vegetation.
• Small remnant ponds.
• An outlet channel cut through the basin margin.
• Different vegetation from the surrounding tundra.
• New polygonal ground developing on the exposed floor.

Why Drained Basins Matter

They influence:

• Regional hydrology.
• Wildlife habitat.
• Vegetation succession.
• Carbon storage.
• Future permafrost development.
• Settlement and infrastructure planning.

Ice-Wedge Polygons and Trough Collapse

Large areas of Arctic tundra display geometric polygon patterns formed above
networks of ice wedges.

How Ice-Wedge Polygons Form

1. Extreme winter cooling contracts the frozen ground.
2. Narrow cracks open at the surface.
3. Snowmelt enters the cracks.
4. The water freezes.
5. Repeated cracking and freezing enlarge the ice wedges.

What Happens When Ice Wedges Thaw?

The surface above the wedges subsides, creating linear troughs around polygon
centers.

These troughs may:

• Fill with water.
• Connect ponds.
• Develop into drainage channels.
• Fragment tundra vegetation.
• Alter snow accumulation.
• Accelerate further thaw.

Low-Centered and High-Centered Polygons

Changes in ice wedges and drainage can transform low-centered polygons into
high-centered polygons as surrounding troughs deepen.

Permafrost Coastal Collapse

Arctic coastlines containing ice-rich permafrost can retreat rapidly when
frozen bluffs thaw and waves remove the weakened sediment.

Processes Acting Together

• Warm air thaws the bluff surface.
• Sea water transfers heat to the coast.
• Waves erode thawed sediment.
• Storms undercut frozen cliffs.
• Blocks collapse onto the beach.
• Sea-ice loss allows waves to reach the shore for longer periods.
• Ground subsidence lowers the coastal surface.

Why Ice-Rich Coasts Retreat Differently

A frozen bluff may appear strong while cold. After thaw, sediment once cemented
by ice can behave like mud or loose debris.

Coastal retreat can expose additional massive ice, producing repeated collapse.

For cliff failures dominated by wave undercutting and rock or sediment collapse,
see:

Coastal Cliff Collapse Explained
.

Mountain Permafrost and Rock-Slope Failure

Permafrost also occurs within high mountain bedrock, talus slopes and debris.
Frozen water can occupy fractures and contribute to the stability of steep
slopes.

How Thaw Can Weaken Mountain Slopes

• Ice in fractures melts.
• Rock joints lose frozen bonding.
• Water pressure changes within cracks.
• Freeze-thaw cycles loosen blocks.
• Previously frozen debris becomes mobile.

Possible Outcomes

• Rockfalls.
• Rockslides.
• Rock avalanches.
• Debris flows.
• Collapse of steep frozen sediment.

Learn more:

Rockfalls, Rockslides & Rock Avalanches Explained
.

How Thermokarst Changes Water Flow

Permafrost acts as a barrier that limits how deeply water can infiltrate.
Thaw alters that barrier and reorganizes both surface and underground drainage.

Possible Hydrological Changes

• New ponds and lakes form.
• Existing lakes expand.
• Lakes drain through new channels.
• Wetlands become wetter or drier.
• Surface runoff shifts into deeper groundwater pathways.
• Streams receive more sediment.
• Riverbanks collapse.
• Water chemistry changes.
• Previously isolated basins become connected.

Does Thaw Always Make the Landscape Wetter?

No. Initial subsidence may create ponds and wetlands, but deeper thaw can improve
subsurface drainage and cause surface water to disappear.

Some regions become wetter while others lose lakes and surface moisture.

Thermokarst and Rust-Colored Rivers

Permafrost thaw can expose minerals that were previously frozen. Weathering and
groundwater transport may carry iron and other dissolved materials into streams,
changing water color and chemistry.

Effects on Lakes, Rivers, Wetlands and Ecosystems

Thermokarst can transform habitat over short distances and relatively short
timescales.

Vegetation Changes

• Dry tundra may become wet sedge habitat.
• Forested ground may become ponded.
• Trees may tilt or die as roots become waterlogged.
• Peat plateaus may collapse into bogs.
• Shrubs may expand into newly drained terrain.

Aquatic Effects

• New ponds create habitat for aquatic organisms.
• Lake drainage eliminates or fragments habitat.
• Sediment clouds reduce water clarity.
• Nutrient release can alter productivity.
• Changes in water chemistry affect fish and invertebrates.
• Stream channels may become warmer or shallower.

Wildlife Effects

Thermokarst can alter travel routes, nesting areas, grazing habitat and access
to water for birds, fish, caribou and other northern wildlife.

Carbon Dioxide, Methane and Permafrost Carbon

Permafrost contains organic material that has remained frozen and partly
protected from decomposition.

When permafrost thaws, microbes can break down that organic matter.

Carbon Dioxide

Carbon dioxide is commonly produced where thawed soils are relatively dry and
oxygen is available.

Methane

Methane can be produced in waterlogged, oxygen-poor environments such as thaw
ponds, wetlands and lake sediments.

Why Thermokarst Lakes Matter

Lakes can transfer heat into frozen ground, causing abrupt thaw beneath and
around the basin. Organic-rich sediment may then become available for microbial
decomposition.

Is Every Thermokarst Feature a Major Methane Source?

No. Emissions vary according to:

• Water depth.
• Temperature.
• Organic-carbon content.
• Oxygen availability.
• Lake age.
• Vegetation.
• Ground-ice content.
• Microbial activity.

A Complex Carbon Balance

Thaw can release carbon through decomposition, but new plant growth and peat
formation may absorb and store some atmospheric carbon.

The net result varies across landscapes and through time.

Damage to Roads, Buildings and Pipelines

Infrastructure built on ice-rich permafrost can be damaged when the ground
warms, thaws and settles unevenly.

Common Forms of Damage

• Cracked and wavy roads.
• Tilting foundations.
• Distorted railways.
• Buckled airport runways.
• Broken water and sewer lines.
• Pipeline deformation.
• Leaning utility poles.
• Failure of bridge approaches.
• Drainage ditches turning into thaw channels.

Why Roads Can Accelerate Thaw

Roads change vegetation, snow accumulation, surface reflectivity and drainage.
Dark surfaces may absorb heat, while embankments can trap snow that insulates
the ground during winter.

Why One Side of a Building May Sink

Uneven ice distribution, shade, drifting snow, leaking pipes and differences in
foundation heat transfer can produce highly variable thaw beneath the same
structure.

Risks to Arctic Communities

For northern communities, permafrost degradation is not an abstract geological
process. It can affect homes, roads, water systems, food storage, cultural sites
and access to hunting and fishing areas.

Community-Level Risks

• Foundation failure.
• Road and runway damage.
• Loss of reliable drinking-water infrastructure.
• Erosion of river and coastal settlements.
• Damage to cemeteries and archaeological sites.
• Changes in lake and river access.
• Unsafe travel across thawing terrain.
• High repair and relocation costs.

Local and Indigenous observations are especially valuable because residents
often identify subtle landscape changes before they become visible in regional
datasets.

How Scientists Monitor Permafrost Collapse

No single measurement can capture all forms of permafrost change. Scientists
combine ground observations, remote sensing and subsurface instruments.

1. Borehole Temperatures

Temperature sensors installed at different depths reveal long-term warming and
changes within the permafrost.

2. Active-Layer Measurements

Probes and instrumented sites measure how deeply the ground thaws each summer.

3. Ground-Penetrating Radar

Radar can help map shallow ground ice, frozen layers and subsurface structure.

4. Electrical Resistivity

Frozen and unfrozen ground conduct electricity differently, allowing geophysical
surveys to identify thaw zones.

5. Satellite Radar

Interferometric synthetic-aperture radar can detect small changes in ground
elevation across large areas.

6. Optical Satellite Images

Repeated imagery reveals expanding thaw slumps, changing lake area, coastal
retreat and vegetation disturbance.

7. Lidar

Airborne and ground-based lidar create detailed elevation models that can measure
subsidence and erosion.

8. Drones

Drone surveys produce high-resolution maps of communities, roads, thaw slumps
and unstable shorelines.

9. Lake and Stream Monitoring

Water level, temperature, sediment, chemistry and greenhouse-gas measurements
reveal how thaw changes aquatic systems.

10. Field Mapping and Community Observations

Ground cracks, leaning trees, damaged roads, new ponds and changes in drainage
provide important evidence of active thermokarst.

Can Thermokarst Damage Be Prevented?

Natural thermokarst cannot always be stopped, but engineering and land-use
choices can reduce additional thaw beneath infrastructure.

Common Engineering Strategies

• Elevating buildings above the ground.
• Using pile foundations extending into stable material.
• Allowing cold air to circulate beneath structures.
• Installing passive heat pipes or thermosyphons.
• Using reflective or insulating surface layers.
• Designing roads to limit snow accumulation.
• Maintaining effective drainage.
• Avoiding ice-rich terrain when choosing building sites.
• Monitoring ground temperature and settlement.
• Designing flexible utility connections.

Thermosyphons

Thermosyphons are passive systems that transfer heat from the ground to the cold
winter air. They can help preserve frozen ground beneath selected infrastructure.

Pre-Thawing

In some projects, ice-rich ground is deliberately thawed and allowed to settle
before construction begins.

Why Drainage Management Matters

Ponded water can accelerate thaw. Culverts, ditches and road embankments must be
designed so that they do not unintentionally concentrate water against
ice-rich ground.

Common Myths About Permafrost Collapse and Thermokarst

Myth 1: Permafrost Is Permanently Frozen Forever

The term means that the ground has remained frozen for at least two consecutive
years. It does not mean that thaw is impossible.

Myth 2: Permafrost Is a Solid Underground Ice Sheet

Permafrost can consist of frozen soil, sediment, peat or bedrock and may contain
anything from very little ice to massive bodies of nearly pure ice.

Myth 3: All Thawing Permafrost Collapses

Dramatic collapse occurs mainly where frozen ground contains excess ice.
Ice-poor permafrost may thaw with limited surface subsidence.

Myth 4: Thermokarst Is the Same as a Sinkhole

Thermokarst develops through melting ground ice. Most sinkholes develop through
dissolution, erosion or collapse into underground cavities.

Myth 5: Thermokarst Only Forms in Flat Arctic Tundra

It also occurs in forests, peatlands, river valleys, Arctic coasts and
high-mountain terrain.

Myth 6: Every Arctic Lake Is a Thermokarst Lake

Arctic lakes have many origins. A thermokarst lake specifically involves
thaw-related subsidence.

Myth 7: Permafrost Thaw Only Creates More Lakes

Thaw can create ponds and lakes, but it can also open drainage pathways and cause
existing lakes to shrink or disappear.

Myth 8: Methane Is Released Everywhere at the Same Rate

Greenhouse-gas production varies with water saturation, temperature, organic
matter, oxygen and local hydrology.

Myth 9: Permafrost Collapse Is Just a Slow Process

Regional warming may be gradual, but individual lake drainages, thaw slumps and
slope failures can develop abruptly.

Myth 10: Refreezing the Surface Restores the Original Permafrost

Seasonal winter freezing is not the same as rebuilding thick, long-lived
permafrost or replacing melted ground ice.

Related but Different Ground Processes

Thermokarst vs Sinkholes

Thermokarst is driven by ground-ice melt. Sinkholes are generally associated with
subsurface cavities, soluble rock or underground erosion.

Read:

Sinkholes Explained
.

Thermokarst vs Land Subsidence

Thermokarst is a specific type of thaw-related subsidence. Land subsidence also
includes groundwater withdrawal, mining, sediment compaction and underground
excavation.

Read:

Land Subsidence Explained
.

Thermokarst vs Landslides

Some thaw features involve slope movement, but ordinary landslides can occur
without permafrost or ground-ice melt.

Read:

Landslides & Mudslides Explained
.

Thermokarst vs Solifluction

Solifluction is the slow downslope movement of waterlogged soil in cold
environments. It does not necessarily involve the collapse of ice-rich
permafrost.

Read:

Slow Slope Movements Explained
.

Thermokarst vs Seasonal Frost Heave

Frost heave occurs when ice lenses grow during seasonal freezing and lift the
ground. Thermokarst develops when pre-existing ground ice melts and the surface
subsides.

Thermokarst vs Glacier Retreat

Glaciers are bodies of surface ice that flow under their own weight. Permafrost
is frozen ground. The two can interact, but they are not the same part of the
cryosphere.

Explore Related Strange Sounds Guides

Frequently Asked Questions

Key Takeaways

• Permafrost is ground that remains at or below freezing for at least two
  consecutive years.
• Thermokarst forms when ice-rich permafrost or massive ground ice thaws and the
  land surface subsides.
• The amount and distribution of excess ground ice determine the potential for
  collapse.
• Thermokarst landforms include thaw depressions, ponds, lakes, ice-wedge
  troughs, collapse scar bogs and retrogressive thaw slumps.
• Surface water can accelerate thaw by transferring heat into frozen ground.
• Thermokarst lakes can expand through shoreline thaw and later drain through
  newly formed outlets.
• Thaw can make some landscapes wetter while improving underground drainage and
  drying others.
• Permafrost degradation can damage roads, buildings, pipelines, runways and
  water systems.
• Previously frozen organic matter may decompose and release carbon dioxide or
  methane after thaw.
• Thermokarst is distinct from limestone karst, ordinary sinkholes, seasonal
  frost heave and general land subsidence.

Scientific Sources and Further Reading

• 
  U.S. Geological Survey — Thermokarst and Thaw-Related Landscape Dynamics
  
• 
  U.S. Geological Survey — Evolution of a Thermokarst-Lake Landscape
  
• 
  U.S. Geological Survey — Thermokarst Lakes, Drainage and Drained Basins
  
• 
  National Snow and Ice Data Center — Thermokarst Definition
  
• 
  National Snow and Ice Data Center — Why Frozen Ground Matters
  
• 
  NASA — What Is Permafrost?
  
• 
  NASA Scientific Visualization Studio — Thermokarst Lakes and Arctic Methane
  
• 
  NOAA Arctic Report Card — Permafrost and the Global Carbon Cycle