Glossary of Terms

The following is a list of terms associated with ice and how these terms are used on this site. The terms are divided into sections (Ice terms, Ice Processes, Ridges, Cracks, Holes, Words related to the Lakeice site, General). 

Names For Kinds of Ice

  • Black Ice:  clear ice that forms on the bottom of an ice sheet on a lake or other body of water. It is called 'black' because the water underneath is absorbs most or all of the light.  A more technical term is congelation ice.  On lakes it is usually type  S1 or S2 ice. It has a bunch of other names (see below).  The clearest ice is thin and new.  

Perfect Ice, although there are a number of minor problems outside the view of this picture. 

  • Grey Ice: Grey ice can come about in several different ways.  It is made grey by air bubbles or small cracks in the ice.  Some types of black ice becomes grey over time (especially large grain ice).  Slush ice formed in a variety of ways can range from white to grey. 
  • White ice:  Any ice containing lots of air bubbles.  It is typically snow ice,  splashed out ice or frozen slush.  The term is often used for snow ice (a form of frozen slush). 
  • Slush Ice: Ice made from a frozen slurry of ice and water.   It is another term for white ice.  Slush can come from water saturating snow that fell on top of an ice sheet or snow that fell in the water, discoid frazil that floated to the surface or lake frazil that agglomerates and then gets broken into small pieces or blowing snow that gets blown into exposed water (puddles, cracks, folded ridges, etc).
  • Splash out Ice1: white ice that forms around open water by waves (ripples to big waves) splashing onto the ice or the shore.  On ice sheets it is a good indicator of recently frozen (thin) new-ice holes and frozen ice edges (that may have thin ice beyond them). On large lakes, splashout ice can form very large ramparts along the shore.  

Splashout ice starting to build up early in the season on Lake Champlain. Splashout ice also refers to water splashed out onto an ice sheet at the side of a hole or ice edge.

  • Snow Ice: frozen slush that is white or grey in color from small bubbles trapped when it froze. Most of the time it comes from snow that falls on an ice sheet.  It turns to slush from submergence of the ice sheet by the weight of the snow.  It can also come from snow falling directly into water (snow fall ice) or lake frazil that accumulates on a lee shore.  

Nine inches of white snow ice over nine inches of S1 black ice, late in the season from Joe's Pond VT which is high and has lots of snow. 

  • Layered Ice:  Ice which contains weak layers.  The most common form is snow ice (frozen slush) over slush or water over black ice.  It has been the source of some terrible accidents
  • Mattress Ice:  well thawed and very weak large grain ice (type S1).  It sags dramically underfoot when stepped on. It often takes a few seconds to break through and may allow you to get onto better ice (or shore) before you break through.   Mattress ice is not often encountered. 
  • Candled Ice: well thawed  small grain ice (type S2).  It is the source of many late season swims. 
  • Green Ice, Blue Ice, Clear Ice,:  Other names for black ice
  • Lake Ice:  Some CRREL reports refer congelation ice formed from lake water as lake ice.  More commonly it is called black ice. Here is simply means ice on a lake no matter what type it is. 
  • Snow Fall Ice1 :  Ice that forms from slush formed by snow falling directly into water.  This requires sufficient snow fall (amount and rate) to cool the surface water to 32 deg.  The sheets of delicate surface slush formed by snowfall ice are sometimes blown by light winds into spectacular patterns.  

A thin layer snow slush was gently folded by wind near an ice edge before freezing into snowfall ice. Scale: picture about 4 feet wide.

  • Frazil Ice: Ice that is largely comprised of frazil that floats to the surface. Frazil comes in a couple of forms: discoid (disk shaped) frazil in rivers where turbulance/convection dominates heat transfer and flake ice that forms on wavy lakes and is broken up by collisions with other flakes, typically found at lee shores or lee ice edges. 
  • Pancake Ice: Broken Ice plates where waves keep the ice pieces rubbing and bumping each other.  They have an oval shape and a raised rim of ice debris around their perimeter.  They are found at or near the wave broken edge of an ice sheet.  Another form of  pancake ice is ice that forms in wavy ice as the frazil slush congeals.  This is very common in sea ice and occurs in lake ice as well.  Frazil pancakes are typically smaller than ice edge pancakes.  
  • Ice Grains: the commonly used term for ice crystals. The formation mechanisms for lake ice tend to result in ice with either small  grains (type S2) or  large grains (type S1).
  • Grain-textured ice1,3: Ice that has been warmed enough that the grain boundaries are visible on the surface of the ice.  
  • Small Grain ice:  Typically ice that forms when snow is falling or in wavy, cold conditions.  In an advanced thaw condition small grain ice is often referred to as honeycomb or candled ice.  In this state it is often dark and the groves between the grains are clearly visible.  The technical term is S2 ice
  • Large Grain ice: forms in quiet conditions when the surface water supercools and long needle like blades of ice grow across the thin supercooled surface layer.  These can be seen in any puddle starting to freeze.  Large grain ice is considerably harder and stronger than small grain ice in an advanced thaw condition. The technical term is S1 ice
  • Smooth Ice: See the black ice picture at the top of the page for an example.  Highly sought after by skaters and sailors. It is most often new ice but sometimes it occurs after a thaw when rough ice is made smooth.
  • Rough Ice: Ice that is rough for what you are doing.  The threshold for 'rough' ice on skates is lower than for iceboating which is lower than for snowmobiling which is lower than riding in a wheeled vehicle.
  • Cobblestone Ice: Very rough ice that is thought to be associated with surface melting of large grain ice. 
  • Wind Scalloped Ice  1: Very rough ice associated with sustained, warm, high winds. It often ends the ice season for skating and sailing.  it is likely that cobblestone ice and wind scalloped ice are the same thing.  

Wind Scalloped Ice

  •  Frazil:  small ice crystals that form in turbulent, flowing, slightly supercooled water in rivers  and in modertely windy conditions on lakes and oceans.  Frazil occurs at such low amounts of supercooling that it is believe that it is always seeded by ice (falling snow, ice fog, spray drops that supercool more while they are suspended in the air, etc.)
  • Active Frazil:  When frazil starts to form it takes a little while (on the order of 10 minutes) to grow enough for the latent heat given off to re-warm the slightly supercooled water back to very near 32 degrees.  During this time it readily sticks to itself and other surfaces.  In a river this can result in large buildups on the bottom of the river (anchor ice) and on intake grates of hydroelectric dams. This is mostly a problem with discoid frazil. 
  • Sintering: the process of active frazil sticking to itself 
  • Discoid Frazil:  Frazil that forms in rivers with enough turbulence to mix the surface water with deeper water.  It can occur on lakes where there is sufficient mixing from wind of upper layers of the water column. It retains its disk shape because the high convective heat transfer rates associated with the turbulent conditions melts off pointy dendritc growth and rounds off corners.  
  • Needle Frazil:  Also called spicule frazil. In calmer conditions on lakes and low turbulence rivers, dendritic needles can form in a thin supercooled layer on the surface. 
  • Flake Ice:  Needle frazil develops dendritic growth on the sides of the needles to become flake ice.  The flakes often gather into small agglomerates as shown in the picture below. 

Flake ice that evolved from Needle Frazil: 0.02" thick dendritic ice crystals on the fingers of a neoprene glove. 

  • Flake Ice Slush1:  course to fine grained slush that evolves from broken thin flake ice ice that forms on the surface of moderately wavy water in cold conditions. More...(see the bottom of the article)
  • Frazil Slush:  forms when mixing action  subsides or lots of frazil has formed and it floats to the surface (see Grease Ice and Flake Ice Slush)
  • Slush Balls: Common on lee shores and lee ice edges in cold, moderately wavy conditions. More...
  • Slush:   a slurry of snow or frazil and water. Slush comes in a range of forms and it significantly affects how an ice sheet evolves. 
  • Grease Ice: a term used for frazil slush in the process of becoming P3 ice as it accumulates on the surface.  Grease ice is common on sea ice.  A variation on the theme is reasonably common on lakes as well.
  • Brash (ice): loose small  pieces of ice floating in water or the same in refrozen form.  The term is normally used with arctic ice but it applies to lake ice. It is common to see isolated pieces of thicker ice in a new,  ice sheet. Usually these pieces are reasonably close to an ice edge. 
  • Big Ice: Ice where wind and sometimes currents have a significant effect on ice behavior.  Generally speaking, ice sheets with dimensions larger than a few miles qualify as big ice.  It is considerably more complicated and usually more hazardous than ice sheets on smaller bodies of water. 
  • Pack Ice:  usually refers to large, free floating, polar, salt water ice sheets.  Ice on very large lakes can take  on some of the character of pack ice. 
  • Ice Floe: Large patch of ice that is free floating. Brash Ice is the same thing with smaller pieces.
  • Ice Edge:  The edge of an ice sheet.  They often have a sequence of broken ice and/or splash out ice. 
  • Frozen ice edge: A former ice edge where the ice as advanced further.  This is a common place to find a significant change in ice thickness between the older ice and the newer ice. 
  • River ice:  ice on moving water.  Currents, variable depth, variable flow rate, etc make it difficult to read and assess. It is best to stay off ice over moving water.  If you do go on it, go with people who have experience with the ice on the river of interest.  Stay off rivers with a current speed over 1 ft/sec and be careful on slower rivers.    
  • Agglomerate Ice: This is a general term for ice that has been broken shoved together.  It can range from vertically offset plates to large masses of jumbled ice. It is very common on larger bodies of water and at ice edges. 
  • Ice Shark:  Isolated pieces that stick up and block iceboat runners or skaters who are not paying attention. It can be refrozen brash ice, off set plates (common at tectonic cracks) or a variety of other things.  The are most common on big ice.   The term comes from iceboating because of the damage they can do. 
  • Shell Ice:  Traditionally it is an ice skim that formed on a reasonably shallow  puddle on the ice.  Wet shell ice looks like black ice making it hard to spot.  It is a hazard to skaters and sailors.  Dry shell ice is white as the puddle has drained away before it froze to full depth.  It is much easier to spot and less of a hazard. Fully refrozen wet shell ice is T3 ice. 
  • Soufflé Shell Ice1: Occasionally a deep puddle drains in cold conditions creating an area (some times a large area) of rather strange ice.  It is typically made up a 1/8" crust over several inches of a fragile matrix of ice flakes that holds up the crust.  Click here for more on this relatively uncommon form of shell ice.  A friend suggested the name and it fits better than anything else we came up with. 
  • Puddle 1: water on top of an ice sheet.  This can range from a shallow melt puddle to a 10 foot deep puddle over a fold pressure ridge.    
  • Puddle Ice1: Puddles skim over forming a hazard for anything heavy enough to break  the skim.  It is  called wet shell ice if the underlying water layer is less than a few inches thick. 
  • Overnight Ice1 : Ice that forms in colder overnight temperatures. It is most common in the spring when most days are above freezing.  The harder surface created by overnight ice on the top of a well thawed ice sheet is the source of considerable over-confidence.  This leads to a lot of swims and fair number of fatalities, particularly among fishermen. 
  • Corn Ice1:  Under sunny conditions in an advanced thaw state, thick ice often devlops a white layer on top.  In its pure form it is made up of small pieces (1/8 inch) that came from the underlying ice. It may also be corn snow in some cases although usually by this stage in the thaw process the snow ice has melted away.   
  • Broken Ice1: Ice that is broken (generally by waves) but not moved around much.  Once the cracks around the pieces refreeze it is usually pretty rough for skating and sailing.  It is usually a sign that you are near an ice edge and possible thin ice on the new ice side of the edge.  It can evolve into pancake ice if the wave action is strong enough. 
  • Stacked Ice1: Ice that has been stacked on itself, sometimes in a vertical position.  It is common in ice edges where there was enough wind to drive loose, broken ice pieces on top of each other. It is one form of aglomerate ice. 
  • seporated Ice1:  Ice that is broken and the pieces have moved apart or overlapped on each other.  This often happens when ice is broken by waves and then drifts appart when the wind subsides.
  • Ice Rubble1:  Ice that has been broken and forms a floating mass of ice pieces. When the ruble mass freezes it it can usually be traversed on skates with some difficulty although it is much easier to negotiate with good foot traction.  
  • Jumbled1 Ice:  ice that has been broken and pushed into piles. It is ice rubble sicks up so much that ot is very difficult to cross on ice skates.   It typically forms when ice broken by wave action is pushed into a more compact pile by waved/strong wind or collisions with ice floes. There are many variations on the theme.

Jumbled ice. The bigger pieces stick up over a foot...Tough skating. 

  • Wet Crack Drifts1:   very common flow-stone like white ice deposits that form along newly formed wet cracks where  blowing snow is caught in the open water of the crack and then acts as a sponge, creating a wet surface for more snow to catch on.  The are often a couple feet wide and an inch high.  It can get 10+ feet wide and a few inches thick.  They can present a tripping hazard for skaters if they are not fully frozen and a skate breaks through the crust.  Also called Snow Bands.
  •  Finger Rafting:  Over thrusting during the collision of two ice sheets.  Finger rafting usually occurs  when the ice is either thin (an inch or less) or thicker and well thawed.  The finger rafting may take place away from the actual collision front, generally at an existing pressure ridge that overthrusts two sheets together as one of them is punted by a colliding floe. 

Remnant of finger rafted thin ice. The far sheet pushed into the near sheet about 50 feet. The ice was an inch or so thick at the time. Finger rafting can occur in much thicker sheets if the ice is well thawed.

  •  Ice Push is defined by NOAA as:  "In hydrologic terms, compression of an ice cover particularly at the front of a moving section of ice cover."    Thick, thawed ice finger rafting is an example of this however there is relatively little compression of the colliding sheets as they ride over and under each other rather than making piles." 
  • Ice Shove is defined by NOAA as: "In hydrologic terms, on-shore ice push caused by wind, and currents, changes in temperature, etcetera"   The most common form is found on large lakes (5+ miles) in the spring on well thawed ice (significantly weakened but still with a fair amount of compression strength) and driven winds in excess of 30 mph.  Ice piles and thick ice finger rafting commonly occur as part of the ice shove process.  An ice shove event typically takes place a short period of time (a few minutes to, maybe, a couple hours).  More on Ice Shoves.

A 12-15' high ice pile from an ice shove event on Maquam Bay on the morning of April 7, 2013

  • Ice Piles:  Piles that form when a large, wind blown ice floe collides with the shore in an ice-shove.  They can also form from wind pressure alone on a very large ice sheet.  Individual ice piles typically form in 15 minutes or less.  They typically form where thick ice finger rafting occurs at the shore. 

A 10 foot high pile of ice from a warm weather ice-shove event. Quaker Smith point, Lake Champlain. 

  • Ice Drift:  Ice sheets that drift as a result of wind or, possibly, currents.  Often it involves a section of an ice sheet being blown into open water.  When it comes to rest against another ice sheet finger rafting may occur.  If it collides with shore ice piles may form.  
  • Anchor ice:  Ice that has frozen to the bottom and is held there as the lake level rises or tide comes in.  It also forms in rivers when slightly supercooled river water is full of frazil.  In this condition the frazil will stick to any surface and can build up very rapidly.  It is a major problem for hydroelectric equipment. Jumbled ice is sometimes incorrectly called anchor ice. 

 Ice Processes and Related Terms

  • Thawing:  The process of ice melting.  It often starts with melting at crystal boundaries.  As the boundaries melt they become less attached to each other weakening the ice dramatically in the late stages of thawing. 
  • Thawed ice is partially melted by warm air and/or sun.
  • Super Cooling:  Water can be cooled well below freezing if there is no ice present to nucleate it. In the formation of ice on a lake the amount of cooling is rarely (if ever) over 0.6 deg F. 
  • Nucleation: The process of starting to form an ice crystal in supercooled water.  Ice is the best nucleating agent.  If the water gets supercooled enough small particles suspended in all lake water will act as nucleation agents.  Clay particles, for example, will nucleate ice at -2 deg F. 
  • Homogeneous Nucleation: Occurs in very pure water.  In clouds  and carefully controlled experiments sometimes get to -40 degrees or colder  before they freeze.   Homogeneous nucleation is not a factor in lake ice because of the large amount of particulate matter in the water.  Also called Spontaneous nucleation.
  • Heterogeneous Nucleation: Nucleation on suspend particles that are not ice. Bacteria or clay particles are examples.
  • Secondary Nucleation: Nucleation that starts from ice in the water (existing pieces and pieces broken off in collisions, snow or ice fog falling into the water, etc). Secondary nucleation is thought to be an important factor in frazil formation. 
  • Crystal axis: Ice forms a hexagonal prism shaped crystal.  The C axis is along the prism.   The six A axes are perpendicular to the C axis and perpendicular to each of the 6 edges between the prism faces (see illustration near the bottom of this page). In supercooled water, ice grows much faster on the A axes than the C axis. Click here for a more detailed explanation.
  • Dendrites:  Dendrites are branched crystals that form in still, supercooled water.  They are more prone to form with more supercooling and sizes over a few mm.  This type of growth accounts for the first skim of ice in calmer conditions without snow falling (P1 and P2 ice)

A 1" dendritc crystal from a mud puddle. If formed in a thin supercooled layer at the top of the puddle. The rounded edge details show that it has melted some. 

  • Fast Growth:  Dendritic ice growing quickly in supercooled water.
  • Slow Growth:  Ice growing at very low amount of supercooling. Typically this is congelation ice forming at the bottom of an ice sheet being cooled by cold air over the ice sheet. 
  • Freeboard:  The amount an ice sheet floats above the water. If the freeboard is more or less than the isostatic equilibrium level there are other factors affecting freeboard.  Examples include thermal expansion stress in the ice that has buckled the ice sheet and extra weight on the ice sheet near by (perhaps you).  
  • Isostatic Equilibrium: For every inch an ice sheet floats above the water level there is 11.8" of ice below the water level to support it.  Likewise, for an ice sheet to support a car (or you) it must depress over a large area enough to displace enough water to equal the weight of the car. 
  • Erosion:  ice melting from moving water.  Common  in rivers and narrow areas in lakes.  Also occurs on the bottoms of puddles in warm, windy weather.   
  • Rotten ice:  Ice that has lost much of its strength from grain boundary melting. Small grain (S2) ice weakens especially dramatically in a well thawed state.  Also called 'well thawed ice' or 'rotten candled ice'. 
  • Rotten Candled Ice1:  well thawed (stage 6), type S2 ice is the source of many spring swims so it gets its own term.   
  • Cold ice:  Ice that is below 32 degrees (even a degree is enough)  and has not had significant internal melting. 
  • Grain Boundaries:  Where grains (crystals) grow into each other.  Boundaries and, especially, triple junctions are the first places to melt in a thaw. Impurities in lake ice get excluded by the crystallization process and end up in the grain boundaries.  This partly accounts for why the boundaries melt before the bulk crystal.
  • Internal melting:  The melting of areas between individual ice crystals (grains) or the formation of Tyndall figures within crystals. This is most strongly driven by sunlight which deposits some of its energy in the ice as it passes through an ice sheet.  
  • Tyndall Figures:  small melt figures that appear in large grain ice that  has been exposed to solar heating.  They are internal melt features that have a variety of shapes.  They are aligned with the basal plane of the crystal. When ice melts it shrinks leaving a water vapor bubble. 
  • Vapor Figure: When melt figures refreeze the vapor bubble often gets separated from the water that it formed with.  When the water freezes it becomes a vapor figure which is usually a thin hexagon. 



The white specs are vapor figures that form when tyndall figures freeze. The line of bubbles that can be seen right at the grain boundaries are filled with air.  They appear to form from excluded disolved air in the melt water that flows through the grain boundaies in warm conditions.

  • Dark Grain Boundaries1: Tyndall figures are not visible within 1/4 inch; to 1/2 inch; of the grain boundaries.  This appears to be a result of melt figures that form from internal radiational heating (sunlight).  Melt figures that form with a connection to a grain boundary will not form a vapor bubble because water can be drawn into the melt figure from its connection with the partially melted grain boundary. With no vapor bubble there will be no vapor figure when the internal melting refreezes (hence the dark color).  
  • Surface melting:  Melting on the ice surface, typically from warm wind, warm temperatures without wind, sun or warm rain.   
  • Triple Junction:  The corner of three ice grains. The first place to melt as ice warms. 
  • Veins: melted triple junctions in rotting ice.
  • Pores: small drain holes that form along grain boundaries (especially triple junctions) in thawed ice that drain water from the surface or let water flow up through an ice sheet submerged under the weight of a snowfall.  

Closeup of frozen pore on moderately well thawed, 5", S1 ice. The white at the top is frozen foam . Scale: white foam is about 3/4" across. 

  • Fall Turnover: When a lake cools off in the fall and early winter, cold water from the surface sinks until the water below the top few feet is all 39°.  This process is called fall turnover and allows wind and thermal convection currents to mix the entire lake from top to bottom. 
  • Winter Stagnation:    Once the lake has an ice sheet and has significantly weaker convection currents, the lake is said to be in Winter Stagnation. It is supported by the fact that water has it maximum density at 39 deg F so water colder than that tends to float rather than skink. 
  • Convection currents: water movement caused density (temperature) differences within the water or currents related to large scale flow of the water. In salt water, salinity differences also drive density currents. In a broader sense, any water movement can  be considered a convection current (for example, wind driven currents). 
  • Currents: gravity flow in rivers and some lakes is a source of all manor of hazards. 
  • Conveyer belt:  Off edge wind blowing the surface water away from the edge of an ice sheet sets up a conveyer belt like current in the lake that eat away at the ice edge.   See: downwind ice edge erosion
  • Seiches: Large underwater waves of cold and warm water set up by wind.  They often account for most of the water flow in a lake.   They are much less active in winter when the water is nearly uniform in temperature and/or if the water is covered by ice.  Even in their less active state they may cause significant erosion of the bottom of an ice sheet although the extent to which this happens is not well understood. . 


  • Pressure Ridges are large scale compression ruptures in the ice sheet, from thermal expansion of an ice sheet.  Also called: reefs, ridges, expansion cracks, cracks, heaves, etc. 
  • Overlapped Pressure Ridge1:  The most common style where one plate overlaps the other, switching sides every 100 feet or so. Also called 'over-under' ridges.   
  •  Folded Ridge1: This type of ridge forms when an ice sheet buckles and  the two new pieces fold down into the water forming a pond several feet deep with ice underneath.   They often evolve into a loose plate ridge.  They are frequently found at the termination of an overlapped ridge or as a side ridge.  In most cases they are less than a few hundred feet long. They always have tectonic cracks at their ends. Other names: push down ridge, fold down ridge, wet ridge. They are the source of many swims in large part because they are harder to see and they often have thin ice or slush on the deep puddle over the folded plates. 
  • Upfolded ridge1: a variation of folded ridges in which the middle of the ridge is folded up. It is rarely more than a foot high and typically has a puddle on each side.  It is comprised of two parallel downfolded ridges. 
  • Loose Plate Ridge1: A ridge that is comprised of a bunch of loose plates.  They often form when the plates of a fold-down ridge  melt enough to get free from each other and float back to the surface.  They are popular places to fall through.
  • Double terminated folded ridge1:  Sometimes a folded ridge will form with no connection to shore or other ridges.  This makes them harder to anticipate. 
  • Along Shore Ridge1:  It is common for ridges to run along the shore, especially if the shoreline is steep enough to resist ice being pushed up on the beach.   
  • Point to Point Ridge1:  The most common form of ridge.  Usually overlap type ridges.  They run from a point on one side of the lake to one on the other. On big ice sheets they may intersect another ridge or simply peter out.
  • Bay Mouth Ridge1: a point to point ridge that runs across a bay entrance. In many places they form every year in nearly the same spot.
  • Melted Ridge1:  The ice in a ridge can partially or completely melt leaving wide bottomless areas along some or all of the ridge.  Folded ridges put the plates into the warmer water found a few feet down. When the plates melt they become a melted ridge. 
  • Pushed Up Ridge1: Older, active ridges in big ice sheets can push up piles several feet high on Lake Champlain and higher on bigger lakes. Like icebergs, for every pound of ice that sticks up,  there is about 12 times that much ice  underneath the water to hold it up.  Inspite of locally thick ice, most ridges have plenty of places to fall through. 
  • Active Ridge: a ridge that is actively absorbing compression and tension movement in the ice sheet.  They can change in as little as a few hours, especially in warming conditions. 
  • Inactive ridge:  The refrozen remnant of a ridge that is no longer active. Often it is replaced by another that runs parallel to it and not far away (50-200 ft away is common). 
  • Tenting:  Ice, typically at ridges with overnight ice on them, that has broken and two pieces push up in a tent like configuration.  

Cracks are fissures created by stresses in the ice sheet. 

  • Tight crack: The very common  cracks visible in all black ice.  They form from both large scale stress in the ice sheet and local thermal stress. They account for a lot of the noise ice makes. 
  • Companion Crack3:  A  crack that runs out in front of you as you move along the ice, typically on cold black ice less than 2.5 inches; thick.  Usually these are not a problem but it is always good to make sure when you hear cracking associated with you.   The name translated from the Swedish term: Kompanjonspricka.  
  •  Zipper Cracks4: Crack that form on black ice that is too thin to be on (roughly1.75"or less).   They may not be obvious to a skater as they are behind them.   

Zipper cracks on Grassy Lake, Maine, 12/19/2010. Guesstimated scale: transverse cracks: 1-1/2 feet apart. Photo: Richard Saltonstall.

  • Wave Cracks1:  Waves or swells will crack the edge of an ice sheet as they roll under it.  Wave cracks play a significant role in ice loss to off edge winds.

Wave cracks about 15 feet apart and more or less perpendicular to the wave direction. 

  • Wet Crack:  Any crack that has water in it.  Contraction cracks are often wet cracks, especially in ice less than a few inches thick.  Some tectonic cracks are wet.  Any wet crack commonly catches blowing snow, creating bands of lumpy white snow ice (wet crack drifts)
  • Wide Wet Crack  A wide crack with open water. Any wet crack more than a couple inches wide can be considered a wide one.   They usually reflect a significant shift in two ice sheets.  On ice that is not fully enclosed by shore and landfast ice wide wet cracks may be an indication that the ice sheet is starting to break up.  They are most common on big ice.  

8" Wide Wet Crack in 6" ice near Panton Vermont, looking south. The ice at the edge of the crack is usually (but not always) close to the full thickness of the sheet. 

  • Contraction Crack1:  Occurs when ice fails in tension as it cools and contracts.  They are usually an inch or less wide.  They are responsible for some of the evening and night ice makes on clear nights.  They are most common in ice less than a few inches thick.   They typically refreeze  in a day or less. They are most common in new black ice less than a few inches thick.  They are the source of many of the snow ice bands that form when there is blowing snow. 
  • Wide Wet Crack: a contraction crack that has not frozen over and is more than 2" wide. When they get bigger than about 2 feet wide they are considered an open lead.  
  • Ice Booming3: The noise ice makes when it ruptures.  Contraction and stress crack formation are common at night when the ice sheet is contracting.  
  • Ice Singing4: The noise new, thin ice makes when it is impacted (with a skipped stone for example) or when skated on. This sort of noise is a good signal to be careful and test the ice a lot until you know how thick and how uniform it is. 
  • Ice Bow3 (formerly called 'Ice Sag' in this glossary): When an ice sheet cools the top cools and contracts resulting in broad concave sections of ice with (generally) dry cracks in between.   The distance between the cracks is determined by the amount of cooling of the top of the ice sheet, ice thickness and other factors. In general it is more than 10 feet and less than 100.  The cracks (properly known as 'dry cracks') are open at the top and catch skates and, on thick ice, iceboat runners. 
  • Ice Bulge : When an ice sheet warms quickly the top expands and causes the ice surface to bend into a convex shape between  cracks that are tight on top and spread apart a little at the bottom. The ice surface at the cracks is likely to be slightly below the equilibrium water level so the cracks may develop small puddles along them.   
  • Tectonic Crack1: Usually associated with pressure ridges, especially where ridges terminate.  They have a characteristic irregularity and are persistent.  If frozen they often have many fracture lines in the ice inside the crack. They can be wet or frozen cracks.
  • Spring  Tectonic Cracks1:  In thawed ice sheets  spring tectonic cracks often replace pressure ridges and contraction cracks as the absorber of daily expansion and nightly contraction.  They act like big contraction cracks from the evening until mid morning.  By the late afternoon they have some of the features of a pressure ridge. 
  • Transverse Crack:  Sometimes folded pressure ridges will terminate and start up again 50-150 feet laterally away. This is an often used way to get around ridges.  There is almost always a wide (4"-12+"), wet crack that runs between the two ridges at roughly right angles to the ridge axes.  
  •  Refrozen Cracks:  The ice is often whiter than the surrounding ice.  If the ice is thick there is generally a fissure an inch or more deep and from 1/8" to several inches wide.  It can catch skates and iceboat runners.  
  • Dry Cracks: a form of stress crack that is open at the top but not full of water (refrozen or otherwise).  They are a tripping hazard for skaters and occasionally they will catch an iceboat runner. They are often associated with 'ice bow' (see above).
  • Open cracks: cracks that are open at the top. Often associated with bowed ice.  They cause a fair number of trips for skaters (try to avoid skating exactly in line with cracks). 
  • Lead:  a long gap between two ice sheets.  Mostly seen on big ice when two sheets are separated by wind or currents. If they are less than about two feet wide they are considered a wide wet crack.   Frozen leads can form a smooth ice path through rough ice. 

Frozen lead in frozen pancake ice. Lead about 30 feet wide. 

  • Shore Lead2 (sometimes called a 'moat'): A band of open water that forms between shore and an ice sheet.  This is most common in the spring when the sun heats shallow water more than deeper water and lake levels often rise.  In an advanced thaw state the ice sheet may be blown away from the shore.
  • Channel Lead2: Elongated opening in the ice cover caused by a water current.  Common under bridges in causeways. 


  •  Hole:  any relatively small (less than a couple hundred feet)  area of open water in an ice sheet.  The term is also used to describe holes that have skinned over but the skin is not thick strong enough to support people or people and their vehicle. 
  • Open water: any area with no ice underneath it (not to be confused with wet areas around pressure ridges if they have ice a few inches to a few feet under the water surface).  The term is also use for large areas of unfrozen lake surface.   Puddles are not considered open water. 
  • Polynaya: A persistent large area of open water in an ice sheet.  The essentially are very large holes.   The term is usually associated with sea ice although it reasonably applies to lakes as well.  
  • Holes in Pressure Ridges:  It is common to find holes or thin ice with no underlying thick plate in pressure ridges, especially after a thaw.
  • Drain Holes: These holes form during thaw conditions when water pools on the surface.  They usually start at a small crack or existing hole an erode into something much larger. 
  • Duck Holes:  Geese and, especially, ducks on the ice are a pretty reliable indicator of open water.  Birds are commonly thought to help keep a hole from freezing.  
  • Saw cut holes for spear fishing and diving:  can be as big as a refrigerator door or bigger.  Hopefully the slab that was cut free will be pulled back in place when the hole is done being used. 
  • Fishing Holes: Drilled.   Typically 4"-10” and they are generally more round than other holes although some inflow holes are pretty darn round. Holes in the 8-10" range are a step through hazard for adults as smaller holes are for children.
  • Gas Holes:  These form where a reasonably steady stream of swamp gas bubbles up from the bottom. They account for a lot of swims and iceboat crashes.  
  • Wind Hole:  These form at small points or other obstructions where the wind is concentrated and swirled by the obstruction,  resulting in thinning and melting mostly on the downwind side of the obstruction.  Wind hole on Shelburne Pond VT-warm winds comes from the right. 
  • Puddle Holes: When a moderately deep puddle forms in windy thaw conditions it can erode through the ice sheet.   The wind warms and pushes the surface water to the downwind side of the puddle.  It returns to the upwind end along the bottom where the warmed  water melts the ice sheet.  They are mostly found in ice thinner than 6". 

A puddle hole in the making

  • Saddlebag Hole1:  a pair of puddle holes that sometimes occur on each side of a thick, water saturated (heavy) snow drift on relatively thin ice. 
  • Rip-out1:  Occurs in high winds when the wind is able to start breaking the ice and then breaks a long down wind slot in the ice.  They may break a mile or more of ice and the slot can be half a mile or more wide. 
  • Blow Out1:  A rip-out that takes out all the ice on a lake or bay. 
  • Reef Hole1:  Areas over reefs often have holes or thin ice.  A popular place for submerging vehicles.
  • Current Hole1: Similar to a reef hole but mostly related to current.  Very common under causeway bridges.   Common on rivers and medium to large lakes.  .  
  • New Ice Hole (formally called Warm Water Hole in this glossary)1:  Occur at first freeze.   They can persist for days or, in a few cases, weeks.
  • Pool: an area of open water that did not close when two ice sheets collide. They are usually a big ice feature.  The term is also used more generally to describe any small area of open water. 
  • Hole Drift1:  a drift that forms where exposed water in a hole catches blowing snow.  While most of these are over small holes like fishing holes and gas holes.  if they form over new-ice holes they can be many feet across (see Slush Hole).  

A 'hole drift' that formed around a fishing hole.  Note:  the snow in the actual hole was removed. 

  • Slush Hole2:  A hole created by water flowing up through an ice sheet, almost always as a sheet is being depressed by a snow fall. They are the are the formation phase of what becomes a star patterns when they freeze.  Formerly called an 'inflow hole' in this glossary.
  • Ice Stars (called Octopus patterns on the lakeice site) : Stars  are frozen patterns associated with water flow up through the ice and into an overlying layer of snow/slush.   Also called Crabs or Octopi.
  • Giant Slush Hole1:  larger holes that catch wind driven snow  making a bottomless snow drift.

Slush Hole: Possibly started as a new-ice hole, then the blowing snow arrived. 

  • Spring Hole:  Usually what is called a 'spring hole' is a new-ice hole or a gas hole.  Real spring holes over springs in the bottom of a lake may exist but the only ones I have found are over underwater culverts.  
  • Mine Field1:  A local term for ice that is full of hidden hazards. An inch of fluffy snow over a gas hole field is a good example:  still skatable but lots of invisible places to put a skate or a skater through. 
  • Weed Hole1:  Aquatic weeds that get frozen into the ice can cause that ice to melt sooner than nearby areas.  This appears to be caused by their dark color absorbing more solar energy than the ice. These are mostly an issue in advanced thaw conditions
  • Thaw hole1:These are fairly large holes that are  found after a significant thaw, generally a windy one. They are often associated with what appear to be tight cracks.   They are probably a mixture of drain holes and puddle holes. 
  • Sun Hole1: Open water created by the sun heating and/or reflecting of a rock or dock.  Most common later in the season. 

Words related to risk:

  • Safe: The most basic definition is: Free from danger or injury. There is nothing about lake ice (or any other activity) that meets this strict definition. The practical version of 'safe' refers to an acceptably low level of risk.  A common use of 'Safety' refers to activities intended to reduce risk.  These two uses are the way 'safe' and 'safety' are used on this site.
  • Risk: The likelihood of a bad outcome of a situation or activity.  Ideally it expressed in terms of the chance of a bad outcome (eg the average mortality risk of driving a car in the US is about 10 fatalities/100,000 people/year).  In most ice related risks we usually don't have a good idea of the exposed population so the best measure we can get is the number of fatalities
  • Outcome:  How things work out.  In general, outcomes are a combination of competence and luck.   A large percentage of bad outcomes are combination of limited skill and bad luck.  
  • Competence:  The combination of knowledge, ability to make good decisions, physical skills and and the ability to protect yourself and others if things go wrong.   
  • Luck: The chance happening of fortunate or adverse events (good luck and bad luck).
  • Situational Awareness: Knowing the ice and other conditions that you might be faced with and understanding the associated risks along with the ability to make prudent decisions and take effective action. It can be thought of as applied competence. 
  • Dodgy Ice:  Ice with a higher than normal risk of falling through for any of many reasons.
  • Treacherous Ice:  Ice with high risk of falling through but the hazard is not easy to see.  Often it has thin ice adjoining thicker ice but the transition from one to the other is difficult to identify.  
  • Swim Rate1:  A slang term for the percentage of a group of ice users that falls through the ice.   For example, In Sweden they estimate that you will swim roughly once in every 100-300 skating trips.  

Miscellaneous Terms

  • Windward shore (upwind shore):  any shore (or ice edge) that off shore wind blows toward the water from the shore or ice sheet. Off shore winds blowing off ice sheets often blow pieces of ice from the edge out into the open water. 
  • Lee Shore:  any shore (or ice edge) that the wind blows toward.  Ice flows pile up there and the edge of an existing ice sheet may be broken up to one degree or another. 
  • Frost Smoke2Condensed water vapor rising above open water in cold conditions.  Also called 'steam'.
  • Wild ice: natural ice that is not improved or approved for activities like skating.
  • Nordic Skating: Long distance skating, usually practiced with long skates with a flat profile.  

 Note 1: Any term marked with with a is created for lack of knowledge of a suitably descriptive term that is in common use.  If you know of more appropriate terms, please get in touch.  Some of these 'created terms' have changed to reflect better choices of words or a better understanding of the thing being described.

Note 2: Term from International Association for Hydraulic Research Terms and Definitions list (1990)

Note 3: Terms from translated Swedish ice terms.

Note 4: Terms in local use

Editing of the glossary: This glossary is edited frequently add new terms, correct errors and improve descriptions. Suggestions welcome.