Why does ice crack? Ice cracks because it is a stiff crystalline solid that can tolerate only limited stretching before bonds fail along a fracture. Cracks form when thermal expansion and contraction, bending, impact, pressure or uneven loading create stresses larger than the ice can redistribute. Because ice is relatively brittle at ordinary frozen-surface temperatures, a tiny flaw can concentrate stress and suddenly grow into a visible fracture.
People searching for why ice cracks, why ice cubes crack in water, why frozen lakes make booming sounds, why glacier crevasses form, why sea ice breaks into leads and why freezing water can break containers are asking about crystal structure, thermal stress, fracture mechanics and phase change at the same time. Different situations share the same core idea: stress becomes concentrated faster than the ice can relax.
For students, cracking ice is a useful materials-science problem. The same substance can behave rigidly over seconds yet flow slowly over months, can fracture at the surface yet deform deep inside a glacier, and can make dramatic sounds without the entire ice sheet failing. Understanding ice therefore requires separating stress, strain, temperature, timescale and geometry.
The Short Answer: Cracks Release Stress
Ice contains microscopic imperfections, grain boundaries and surface scratches. When external or thermal forces load the material, those imperfections concentrate stress.
If local stress exceeds the ice’s fracture resistance, an existing flaw extends and the stored elastic energy is released through a growing crack.
Why Ice Is a Crystal
Ordinary terrestrial ice is mostly ice Ih, in which water molecules occupy an ordered hexagonal crystal structure held together by hydrogen bonds.
That ordered structure gives ice stiffness, but it also means deformation is constrained by how the crystal lattice and grain boundaries can move.
Why Ice Is Brittle
At many everyday subfreezing temperatures and short timescales, ice cannot rearrange internally fast enough to accommodate large tensile strain.
Instead of stretching substantially like rubber, it tends to fracture once stress at a flaw becomes high enough.
Why Ice Can Also Flow Slowly
Under sustained stress over long periods, especially at warmer subfreezing temperatures and high pressure, ice can deform by creep.
Glaciers exploit this slow ductile behaviour even though the same ice can crack suddenly when loaded rapidly near the surface.
Why Timescale Changes Ice Behaviour
A force applied in milliseconds gives molecules little time to rearrange, favouring brittle fracture. The same stress applied over months may produce gradual crystal deformation.
Materials can therefore look solid and fragile in one experiment yet flow in another without changing chemical identity.
Why Tiny Flaws Matter
A perfectly uniform solid would distribute load more evenly, but real ice contains bubbles, scratches, impurities and grain boundaries.
The tip of a flaw concentrates stress into a very small region, allowing a crack to grow even when average stress across the whole piece is much lower.
What Stress Concentration Means
A notch or crack changes how force travels through a material. Lines of stress crowd around the sharp tip.
The sharper the defect, the more strongly local stress can exceed the average load applied to the ice.
Why Cracks Grow Suddenly
As a crack lengthens, the stressed region at its tip can become even more intense. If the energy released by further cracking exceeds the energy needed to create new surfaces, the fracture can accelerate.
This is why a quiet sheet of ice can produce a sudden sharp crack without a slow visible warning.
Why Ice Cracks Branch
A fast crack changes the local stress field as it moves. Multiple fracture paths can become favourable.
The result can be branching white lines or star-like patterns rather than one perfectly straight fracture.
Why Crack Surfaces Look White
Air-filled gaps and rough fracture surfaces scatter light strongly.
Even clear ice can develop bright white crack lines because the new interfaces redirect light in many directions.
Why Water Can Make a Crack Less Visible
If liquid water fills a gap, the difference in refractive index between the crack and surrounding ice becomes smaller than with air.
The fracture may therefore look darker or partly disappear optically even though the structural break remains.
Why Ice Cubes Crack in Water
A very cold cube dropped into warmer water heats unevenly. The outer region warms and expands sooner while the interior remains colder.
That temperature gradient creates internal stress. If it exceeds the cube’s fracture resistance, cracks form with the familiar sharp sound.
Why Ice Cubes Crack in Drinks
The same thermal-shock mechanism occurs when freezer-cold ice enters a beverage that is much warmer.
Rapid surface warming creates a mismatch in expansion between the outside and the colder core, producing tensile stress inside the cube.
Why Hotter Liquid Can Produce More Cracking
A larger temperature difference can create a steeper thermal gradient and stronger differential expansion.
The outcome still depends on cube size, bubbles, prior cracks and how quickly heat moves into the ice.
Why Slow Warming Causes Less Thermal Shock
If temperature changes gradually, heat has more time to spread through the whole piece.
Smaller temperature differences develop between the surface and centre, reducing internal stress concentration.
Why Ice Cracks When Removed From a Freezer
A frozen object entering warmer room air begins warming at the surface first.
For thick pieces, the resulting thermal gradient can create audible cracks even without any obvious external force.
Why Uneven Cooling Can Also Cause Cracks
When water freezes from one region before another, the solidifying portion can constrain material that is still cooling or expanding elsewhere.
Internal stress can develop before the ice is ever handled, leaving flaws that later grow under small loads.
Why Water Expands When It Freezes
Most substances contract on freezing, but ordinary water forms an open hydrogen-bonded crystal structure that occupies more volume than liquid water near the freezing point.
The volume increase is roughly nine percent, large enough to create substantial pressure if expansion is strongly confined.
Why Freezing Water Can Break Containers
If a rigid sealed container leaves no room for expanding ice, pressure rises as more water freezes.
The container may crack or deform because the phase change imposes strain the walls cannot accommodate.
Why Pipes Can Burst During Freezing
Ice blockage can isolate liquid water inside a pipe while continued freezing and expansion raise pressure.
The pipe often fails where pressure becomes highest rather than exactly where the original ice plug first formed.
Why a Frozen Bottle Can Split
Water expanding into ice needs additional volume. A full rigid bottle provides too little free space.
Pressure transfers to the container walls until the bottle deforms, its cap moves or the material fractures.
Why Frozen Lakes Crack
Lake ice experiences temperature swings, snow loading, wind, water-level changes and local bending.
Because the sheet spans a large area, small thermal strains accumulated over hundreds of metres can generate substantial stress.
Why Cooling Makes Lake Ice Contract
As solid ice cools further below its freezing point, its dimensions generally decrease.
If different regions cool by different amounts or the shore constrains movement, tensile stresses can open cracks.
Why Warming Can Also Stress Lake Ice
Warming expands the ice sheet. If shorelines or adjacent ice resist that expansion, compression builds.
The ice may buckle, ridge or push against the shore rather than simply growing smoothly in every direction.
Why Frozen Lakes Make Booming Sounds
A long fracture can release elastic energy rapidly and launch sound waves through the ice.
The sheet can act like a giant resonating plate, producing booms, pings and science-fiction-like tones over large distances.
Why Some Lake-Ice Sounds Change Pitch
Different wave frequencies travel through ice at different speeds, and long cracks can excite many frequencies at once.
As the sound disperses across the sheet, listeners can hear descending or sweeping tones rather than one simple snap.
Why a Loud Crack Does Not Automatically Mean Total Failure
Cracking is evidence that stress has been released locally, not necessarily that an entire ice sheet has lost all load-bearing capacity.
However, sound alone cannot determine safety; local conditions, water flow, weather and professional assessments matter.
Why Ice Safety Cannot Be Judged From One Crack
Thickness can vary over short distances because of currents, springs, snow insulation, structures and changing temperatures.
A general article cannot establish whether natural ice is safe to walk or drive on; local authorities and site-specific measurements are required.
Why Snow Changes Lake Ice
Snow insulates the ice from cold air, slowing heat loss and altering how quickly new ice thickens.
Its weight can also depress the ice surface and influence flooding, slush formation and mechanical stress.
Why Clear Ice and Snow Ice Differ
Clear columnar ice often forms from direct freezing of lake water, while snow ice can form when slush or flooded snow refreezes.
Their bubble content, grain structure and mechanical properties differ, so equal thickness does not guarantee identical strength.
Why Bubbles Matter
Air bubbles interrupt the otherwise continuous crystal and can act as local defects.
A bubble does not always cause fracture, but it can alter stress distribution and provide a site where a crack initiates or changes direction.
Why Impurities Matter
Salts, sediment and organic material change freezing behaviour and can concentrate at grain boundaries or brine pockets.
These heterogeneities create mechanical weak points and make natural ice more complex than laboratory-pure frozen water.
Why Sea Ice Is Different From Freshwater Ice
Seawater contains dissolved salts that are mostly excluded from the growing ice crystals, leaving concentrated brine in channels and pockets.
Sea ice is therefore a porous saline composite whose strength, flexibility and fracture behaviour depend strongly on temperature and brine content.
Why Sea Ice Forms Leads
Wind and ocean currents pull pack ice apart, opening long fractures or gaps called leads.
The cracks expose seawater, change heat exchange with the atmosphere and can later refreeze into new thin ice.
Why Sea Ice Forms Pressure Ridges
When moving ice floes are pushed together, compression can break edges and stack blocks upward and downward.
The resulting ridges are the compressional counterpart to open leads formed by tension.
Why Wind Can Crack Sea Ice
Wind transfers force to broad ice surfaces. Because floes are constrained by neighbouring ice and coastlines, differential motion generates tension, shear and compression.
Fracture lets the pack reorganise in response to those large-scale forces.
Why Tides Can Crack Coastal Ice
Rising and falling water levels flex shore-fast ice and move floating sections relative to fixed land.
Repeated bending concentrates stress near grounding points, cracks and structural boundaries.
Why Currents Create Weak Zones
Moving water transports heat and can thin ice from below. It also changes mechanical support beneath the sheet.
Areas above currents can therefore behave very differently from nearby still-water ice despite looking similar from above.
Why Glaciers Develop Crevasses
A glacier flows under its own weight. Where the surface is stretched faster than ice can deform ductilely, brittle cracks open.
These deep surface fractures are called crevasses and commonly form where glacier speed or direction changes.
Why Glacier Ice Flows but Still Cracks
Deep warm ice under pressure deforms slowly, while colder near-surface ice is more brittle.
A glacier can therefore flow as a whole while its upper tens of metres fracture under tensile stress.
Why Crevasses Form Near Steep Slopes
As a glacier accelerates over steeper terrain, upper ice can be stretched longitudinally.
If strain accumulates faster than brittle ice can accommodate, transverse crevasses open across the flow.
Why Crevasses Form Near Valley Walls
Ice near valley sides experiences drag while the centre may move faster.
Shear stress between these regions can produce crevasses oriented at angles to the main flow.
Why Crevasses Can Close
When glacier flow enters a compressive region, ice can be pushed together and fractures can narrow or become buried.
The same moving glacier therefore creates cracks in extending zones and closes them in compressing zones.
Why Crevasses Can Be Hidden by Snow
Snow can bridge across an open crack and form a surface that looks continuous.
The hidden geometry below can remain dangerous, which is why glacier travel requires specialised local knowledge and safety practice beyond visual inspection.
Why Ice Shelves Crack Into Rifts
Floating ice shelves are stressed by glacier flow, ocean tides, bending and interactions with islands or seafloor features.
Long fractures called rifts can grow for kilometres and eventually participate in calving large icebergs.
Why Icebergs Break Off
When fractures penetrate enough of an ice shelf or glacier front, ocean and gravitational forces can separate a large block.
Calving is a fracture process acting on ice that is also flowing and deforming over much longer timescales.
Why Ice Can Shatter Under Impact
A sudden blow deposits energy faster than brittle ice can redistribute through plastic deformation.
Multiple cracks can propagate from the impact point, fragmenting the material into many pieces.
Why Thin Ice Can Flex More Before Breaking
A thin sheet can bend noticeably under load, but bending creates tension on one face and compression on the other.
If tensile stress exceeds fracture strength, the sheet cracks even though it first appeared flexible.
Why Thick Ice Can Crack Too
Greater thickness raises bending stiffness but does not eliminate thermal stress, defects or large-scale loading.
Cracking depends on stress relative to fracture resistance, not on thickness alone.
Why Corners Promote Cracks
Sharp corners and notches concentrate stress because force pathways must bend around a small radius.
Rounded shapes distribute load more smoothly, which is why engineering designs often avoid sharp internal corners in brittle materials.
Why Scratches Weaken Ice
A scratch is a pre-existing surface flaw. Under tension, its tip concentrates stress and can become the starting point of a larger crack.
The same fracture-mechanics principle applies to glass, ceramics and many other brittle solids.
Why Grain Boundaries Affect Fracture
Natural ice is usually polycrystalline, made of many crystals with different orientations. Boundaries between grains alter how stress and deformation move through the material.
A crack may cross a grain, follow a boundary or change direction depending on local structure.
Why Crystal Orientation Matters
Ice crystals are anisotropic: mechanical properties differ with crystallographic direction.
In a polycrystalline sheet, the average behaviour emerges from many grains oriented in different ways.
Why Warmer Ice Can Deform More
As ice approaches its melting point, molecular rearrangement and crystal creep become easier.
Under slow loading, warmer ice can accommodate more strain before brittle fracture than colder ice, though the exact response depends on rate and structure.
Why Very Cold Ice Can Be More Brittle
Lower temperature suppresses time-dependent deformation mechanisms.
Stress is therefore more likely to remain concentrated and drive sudden cracks under rapid loading.
Why Crack Speed Can Be High
Once unstable fracture begins, stored elastic energy is converted quickly into creation of new surfaces and motion.
A crack front can travel far faster than the slow external load that originally built the stress.
Why Cracking Makes Sound
Rapid fracture displaces material and launches elastic waves through both the ice and surrounding air.
The audible snap is therefore energy released mechanically, not the crack itself “making noise” as a separate process.
Why Cracking Sounds Travel Far Through Ice
Solid ice can transmit elastic waves efficiently, and large sheets provide continuous paths over long distances.
A crack kilometres away can sometimes be heard as the wave reaches another part of the sheet.
Why Ice Can Ring or Sing
Thin plates and large sheets have natural vibration modes. A fracture can excite those modes like striking a giant instrument.
Dispersion and resonance create tones very different from the simple crunch of crushed ice in a glass.
Why Cracked Ice Sometimes Refreezes
If liquid water fills a crack and temperatures remain below freezing, new ice can form inside the gap.
The healed region may differ in crystal structure, bubbles and strength from the original surrounding ice.
Why Refrozen Cracks Can Still Be Visible
Trapped air, snow, impurities and different crystal textures scatter light differently from undisturbed ice.
A crack line can therefore remain visible even after the gap has frozen closed.
Why Repeated Freeze-Thaw Cycles Damage Rock
Water enters pores and cracks in rock, then expands when it freezes. Repeated pressure and thawing can gradually widen fractures.
This process contributes to physical weathering in cold climates, linking ice fracture to landscape change.
Why Ice Can Crack Concrete and Pavement Indirectly
Water entering joints or porous material can freeze and expand, while frost heave can move the ground beneath structures.
Damage comes from confined expansion and repeated mechanical cycling rather than ice chemically attacking the material.
Why Frozen Food Can Develop Cracks
Different parts of food freeze and shrink at different rates, while growing ice crystals alter internal structure.
Thermal gradients and phase changes can create fractures in frozen desserts, fruit or prepared foods.
Why Ice Cream Usually Does Not Crack Like an Ice Cube
Ice cream is a multiphase mixture containing ice crystals, fat, sugar, proteins and air.
Its softer continuous matrix allows more deformation and distributes stress differently from a solid block of nearly pure ice.
Why Salt Changes Ice Cracking
Salt lowers the freezing point and creates brine-rich regions that remain liquid at temperatures where pure water would be solid.
The mixed structure can change stiffness, fracture strength and the way cracks propagate.
Why De-Icing Salt Weakens Surface Ice
Salt dissolves into surface water and lowers its freezing point, causing some ice to melt even below zero degrees Celsius under suitable conditions.
The result is a porous, wet and mechanically altered surface rather than a pristine solid sheet.
Why Ice Cracking Is a Good Fracture-Mechanics Lesson
Cracking depends on flaws, stress concentration and energy release, not simply on total force.
A small sharp defect can matter more than a much larger smooth feature because fracture begins locally.
Why Ice Cracking Is a Good Thermal-Physics Lesson
Uneven temperature creates uneven expansion and contraction.
A cold core and warmer surface can pull against each other strongly enough to break the material without any external impact.
Why Ice Cracking Is a Good Geology Lesson
Glacier crevasses, sea-ice leads and frost weathering all use the same basic material but different sources of stress.
The behaviour of ice helps shape landscapes, oceans and polar environments.
Why Ice Cracking Is a Good Timescale Lesson
Ice can crack in milliseconds, bend over hours and flow over centuries.
Material behaviour changes with the rate at which stress is applied, making timescale as important as temperature or thickness.
Why Ice Cracking Is a Good Evidence Lesson
A visible crack tells us fracture occurred, but not automatically why. Thermal shock, bending, impact, tides, glacier flow and confined freezing can produce similar-looking breaks.
Good explanation requires context, geometry and loading history.
Common Myths About Cracking Ice
A loud crack does not automatically mean an entire lake is failing, thick ice is not immune to fracture and water expansion is not the cause of every crack in existing ice.
The broad mechanism is stress exceeding local fracture resistance.
Frequently Asked Questions
Why does an ice cube crack in a drink? Rapid uneven warming creates thermal stress. Why do frozen lakes boom? Long fractures release elastic waves through a large ice sheet. Why do glaciers crack? Surface ice is stretched faster than it can deform.
Why can freezing water break a container? The phase change expands water and generates pressure when expansion is confined.
Where to Go Next
Ice cracking connects naturally to the wider water, weather, materials and Earth-science ecosystem on eduKateSingapore.
Ice cracks because it is strong enough to store elastic stress but brittle enough to release that stress suddenly through fracture. Temperature, load, defects and timescale determine where and when the break appears.
Why Lake Ice Can Crack on a Clear Cold Night
After sunset, the upper surface can cool rapidly while deeper ice remains warmer. The colder upper layer contracts first, creating a temperature gradient through the sheet.
If the sheet is constrained by shorelines or neighbouring ice, thermal contraction builds tensile stress until a crack opens and releases it.
Why Sunny Days Can Create New Stress
Sunlight warms the upper ice and can create a different temperature profile from the one established overnight. Expansion near the surface may be resisted by colder material below.
Repeated daily cycles therefore load and unload the ice even without anyone walking on it.
Why Shorelines Constrain Ice
A floating sheet would prefer to expand and contract freely, but ice frozen against shore, rocks, docks or fixed structures cannot move uniformly.
Constraint converts ordinary thermal expansion into mechanical stress, especially across large distances.
Why Ice Pushes Against Shore
When warming causes expansion, the sheet can exert force on beaches, retaining walls and structures. Repeated movement may pile material or shove shoreline objects.
The same thermal cycle that opens tension cracks during cooling can create compression damage during warming.
Why Pressure Ridges Can Be Dramatic
Large sheets pushed together cannot occupy the same space. They fracture and stack blocks upward and downward, forming ridges that can be metres thick.
Compression therefore transforms a flat sheet into a rough three-dimensional structure rather than simply crushing the ice invisibly.
Why Thin New Ice Sounds Different
A thinner plate has different natural vibration frequencies and flexes more under small disturbances. Cracks can excite higher-pitched resonances.
Thicker sheets tend to support lower-frequency modes, so changing thickness alters the soundscape even when the same fracture mechanism operates.
Why Ice Can Make Laser-Like Sounds
Dispersive waves in a large ice plate cause different frequencies to travel at different speeds. A sharp crack contains many frequencies at once.
By the time those waves reach a listener, they can arrive in a sweeping sequence that sounds electronic or otherworldly.
Why Crack Length Changes the Sound
A longer fracture releases energy over a larger region and can excite lower-frequency vibrations in the sheet.
Short surface cracks tend to produce sharper local sounds, while long propagating fractures can create booming signals that travel farther.
Why Crack Direction Matters
Stress is not identical in every direction. A crack tends to grow along a path that releases the most energy under the current loading.
Crystal orientation, existing flaws and sheet geometry can therefore steer the fracture rather than forcing a straight line.
Why Cracks Sometimes Stop
A crack can enter a region with lower stress, tougher structure or different grain orientation. The energy available for further growth may then fall below the fracture threshold.
Crack arrest is one reason natural ice can contain many short fractures instead of one break crossing the entire sheet.
Why Cracks Sometimes Join
Two nearby fractures alter the stress field around one another. If their tips approach, the stressed zones can interact and encourage coalescence.
Joined cracks create a larger structural defect and can redirect how the surrounding sheet carries load.
Why Loading Speed Matters on Ice
A rapidly applied load gives the material little time to redistribute stress by creep. Brittle response therefore becomes more likely.
Slow loading can allow more time-dependent deformation, especially in warmer ice, though safety cannot be inferred from this principle alone.
Why Repeated Loads Can Matter
Repeated bending or vibration can extend existing flaws incrementally even when one individual load does not cause immediate failure.
Natural ice experiences repeated forcing from waves, wind, vehicles, tides and temperature cycles, so damage history matters.
Why Ice Strength Varies Across One Lake
Water depth, currents, springs, snow cover, vegetation, structures and recent weather all change how ice forms and thins locally.
Two points only a short distance apart can therefore have different thickness, grain structure and fracture resistance.
Why Moving Water Is Especially Important
Currents transport heat from deeper or upstream water and can slow freezing from below. They also undermine the mechanical uniformity of the sheet.
This is why visual appearance alone cannot establish whether natural ice has the same strength everywhere.
Why Snow-Covered Ice Is Hard to Judge Visually
Snow hides cracks, slush, thin spots and changes in ice colour. It also insulates the sheet and changes growth rate.
Surface uniformity can therefore conceal very nonuniform structure underneath.
Why Natural Ice Safety Requires Local Assessment
General rules about cracking, colour or nominal thickness cannot account for every current, spring, recent thaw or pressure ridge. Conditions can change rapidly.
Decisions about travel on natural ice should rely on local authorities, professional measurements and site-specific guidance rather than internet rules of thumb.
Why Glacier Crevasses Can Be Very Deep
Near the surface, low pressure and cold temperatures favour brittle fracture. Deeper down, increasing pressure and warmer ice promote ductile flow that tends to close cracks.
This creates a characteristic depth range in which open crevasses can persist before deeper flow becomes dominant.
Why Glacier Crevasses Form Patterns
Stress fields repeat across a flowing glacier. Similar stretching or shear along a region creates families of crevasses with related orientations.
The pattern is therefore a map of how the glacier is deforming, not random surface damage.
Why Crevasses Can Curve
As ice continues to flow after a crack forms, different parts of the glacier move at different speeds and directions. The fracture is carried and rotated with the flow.
Its final shape can therefore record both the original stress orientation and later glacier motion.
Why Icebergs Can Fracture After Calving
Once detached, an iceberg adjusts to a new buoyant equilibrium. Uneven melting, waves and internal stress can cause additional cracking and breakup.
The fracture history therefore continues after the iceberg leaves the glacier or ice shelf.
Why Sea-Ice Floes Grind Against One Another
Wind and currents move neighbouring floes at slightly different speeds. Contact creates compression, shear and abrasion along their edges.
Cracking and ridge formation are therefore part of the normal mechanical life of pack ice.
Why Sea-Ice Cracks Can Refreeze Quickly
An open lead exposes relatively warm ocean water directly to cold air. Strong heat loss can freeze a new thin skin rapidly.
The fresh ice is younger, thinner and mechanically different from the surrounding older floes until it thickens.
Why Thermal Cracks Recur Along Old Lines
A healed fracture can retain altered grain structure, trapped bubbles or geometric irregularity. Those features may continue concentrating stress during later temperature cycles.
The same broad line can therefore reopen repeatedly rather than every new crack choosing a completely fresh path.
Why Cracking Can Be Useful to Scientists
Acoustic emissions, crack patterns and deformation measurements reveal how ice stores and releases stress.
Researchers use these signals to study glaciers, sea ice, lake ice and engineering problems involving frozen materials.
Why Ice Is a Useful Fracture-Test Material
Ice can be produced with controlled temperature, salinity and grain size, allowing researchers to test how fracture changes with known variables.
The lessons extend to other brittle materials because stress concentration and crack-energy principles are widely shared.
Why Cracking Ice Connects Physics and Earth Science
The same fracture mechanics explaining an ice cube in a glass also helps explain crevasses, leads and pressure ridges on planetary scales.
Scale changes the forces and geometry, but the core competition between stress and material resistance remains recognisable.
What Students Should Be Able to Explain
A strong answer should connect crystal structure, flaws, thermal gradients, tensile stress and brittle fracture. It should also distinguish cracking caused by existing ice stress from pressure generated when liquid water freezes and expands.
If the learner can explain ice cubes, booming lakes and glacier crevasses using the same stress-and-fracture model, the topic has become transferable understanding.
The Big Picture
Ice cracks whenever stored stress becomes easier to release by creating a new fracture surface than by continuing to deform elastically or creep. Temperature, geometry, flaws and loading rate decide when that threshold is crossed.
That is why cracking ice can be a tiny snap in a drink, a booming lake, a kilometre-long sea-ice lead or a glacier crevasse—the scale changes, but the fracture logic remains the same.