Ice Terminology and Relevant Numbers 

These definitions are ice oriented and are intended to be easy to understand rather than rigorous. More comprehensive definitions can be found on the www.

  • Pressure: often used to describe compressive stress in ice (as in  'pressure ridge': a compression feature).
  • Stress:  the amount of force in the ice (force/unit area)  Common units are: lb/square inch or Pascals
  • Strain:  the amount of deformation in the ice.  Units are deformation per unit of length. (example of units:  inches of deformation per inch of ice). 
  • Poisson's Ratio: 0.33:   In tension, it is the ratio of tensile elongation to thinning across the axis of the tensile strain.
  • Stiffness Modulus:  Modulus is the inherent stiffness of a material.  Ice is about 1,500,000 psi (10 GPa). This is about the same as hardwood bent along the grain.  Examples of moduli for common materials: a rubber band has a modulus of about 5,000 psi, most hard plastics are around 500,000 psi and steel (mild and hard) is about 30,000,000 psi. Salt ice has a significantly lower modulus.
  • Density of ice:  0.916 g/cc at 32 degrees F
  • Density of water:  1.000 g/cc at  39 degrees F and 0.99987 g/cc at 32 deg (and 46 deg). This is a result of hydrogen bonding.  (see 'Melting Point' below). 
  • Coefficient of expansion: Un-constrained ice expands 0.000028 inches/inch of length/deg F ( 0.000050 cm/cm of length/deg C)
  • Tensile strength:  Strength in tension:  about 150 psi (1 MPa) for cold ice. 
  • Flexural strength:  what really matters:  about 150 psi for unthawed ice. Flexural strength is limited by tensile  strength in most situations.   Ice has a flexural strength about the same as white pine ACROSS the grain (which is about 1/50th of its flexural strength along the grain). 
  • Compressive strength: about ten times the tensile strength for cold ice.
  • Elongation at failure in tension:  0.01% (not very much).  Wood,  hard steel and strong aluminum fail or yield at about 1% elongation. Natural rubber fails at several hundred percent.
  • Yield Strength:  Ice shows brittle behavior when loaded to failure in time frames of less than a minute.  The yield strength is effectively the same as the failure strength. See 'Creep' below.
  • Heat of melting: 80 cal/g   The energy required to melt ice (or that must be removed from water to freeze it).  Also called latent heat, the heat of fusion or enthalpy of fusion. In simple terms, it is the amount of energy required to allow the molecules to go from wiggling in solid ice to wiggling, rolling and sliding around in a liquid.
  • Heat of evaporation: 540 cal/g The energy required to turn water into water vapor.
  • Heat capacity of Ice: 0.50 cal/g/deg C:  The energy required to increase the temperature of a gram of ice one degree C. 
  • Heat capacity of Water:  One calorie/gram/deg C (this is higher than most other compounds)  
  •  Heat capacity of Water Vapor: 0.48 cal/g/deg C
  • Vapor Pressure:  about 4 mm Hg just below freezing (0.5% of atmospheric pressure).  This is the partial pressure of water vapor at 32 degrees. 
  • Fracture Toughness: a measure of how easily a crack propagates through something.  Ice has a very low fracture toughness:  about 1/10th as much as window glass. 
  • Thermal shock resistance:  Ice cubes from the freezer will often crack from thermal shock then they are put into cool water.  The thermal shock parameter for ice is about 1/20th of the value for window glass. 
  • Coefficient of friction:  0.004 for a kicksled is the lowest I have measured and consider valid.      0.005 is typical for speed skates and iceboat runners on good, near freezing ice.  Hollow ground skates like hockey and figure skates have significantly higher friction.   The test speeds were 1 to 5 mph.  The speed and time to stop were measured with a logging GPS. Measuring values this low is tricky.  It has to be windless and the test needs to run on the same ice in opposite directions to minimize the effects of slight slope that can be found on any ice sheet.  The coefficient of friction increases as the ice temperature drops.
  • Quasi-liquid surface:  The current understanding of ice is that molecules near the surface are sort of attached and sort of loose when it is near its melting point. This is what is believed to make ice slippery.
  • Pressure-induced reduction of melting point (near 0° C): 0.074° C/MPa.  This amounts to about  1° C of melting point reduction at 10 MPa, the compression strength of ice near its melting point which is why pressure is not a big factor in why ice is slippery.
  • Melting Point: At normal pressure, ice melts at 32 deg F.  This is much higher than similar materials like ammonia (NH3 melts at -108 deg) or hydrogen fluoride (-118 deg).  This reflects the the large amount of hydrogen bonding that occurs in cold water.  Groups of H20 molecules gather together forming what is effectively a much larger molecule with a higher melting point.
  • Thermal Conductivity of Water: 0.34 BTU/ft-hr-°F
  • Thermal Conductivity of Ice:  1.26 BTU/ft-hr-°F  (3.8x water)

Technical Processes and Terms

  • Creep: Glaciers flow slowly down hill.  This flow is a result of the ability of ice to slowly plastically deform when it is under high pressure.  The amount of confining pressure on ice sheets on lakes is too low for creep to be a significant factor.  For the most part, lake ice behaves as a brittle solid. A combination of creep and brittle failure seems to account for broad shallow folds sometimes seen in thicker, older, warm ice.
  • Sublimation: The process of evaporating directly from a solid to a gaseous state.
  • Super Cooling:  Pure water can be cooled well below freezing if there is no ice present to nucleate it.
  • Nucleation: The process of starting to form an ice crystal in supercooled water.  Ice is the best nucleating agent for itself.  If the water gets supercooled enough (a couple of degrees or less) small particles suspended in all lake water will act as nucleation agents.
  • Homogenous Nucleation: Nucleation from ice.  On example is snow or ice fog falling into supercooled water on the surface of a lake.  Another is discoid (river) frazil which careful experiments have shown nucleates at about -0.05 deg C.  Even though the specific source is still not clear it is believed that it is ice particles.
  • Heterogonous nucleation:  Nucleation from things other than ice (suspended particles, bacteria, pollen, etc).
  • Spontaneous Nucleation: Nucleation of pure water by temperature alone. Cloud droplets nucleate at about -40 deg.
  • Crystal axis: Ice forms a hexagonal prism shaped crystal.  The C axis is along the prism.   The A axes are perpendicular to the C axis and are along the corners between the 6 faces of the prism faces.

  • A axis:  The a axis is perpendicular to the crystal edges of the prism planes.  Ice grows much faster along the A axis in supercooled water.
  • Dendritic growth:  Ice growing in supercooled water. It typically grows as needles or branched needles which are called dendrites.  Dendritic growth is also called fast growth. 
  • Congealation Ice: ice that grows on the bottom of an ice sheet as a result of cold air over the ice sheet.
  • Linear Polarized Light:  Light who's electrical field axis vibrates in one plane.
  • Linear Polarizier: For ice observation, it is a sheet of plastic with very narrow parallel lines in it that allow only the portion of the light that is alligned with the filter to pass.  This amounts to a little less than half of the incoming light.   Two polarizers at right angles to each other will block almost all the light.  If a thin piece of ice is placed between them the light passing through the first filter is rotated by the ice so that it can can pass through the second filter.  The color of this light depends on the thickness of the piece of ice and orientation of the crystal the ice passes through.  It  is a colorful way to see ice crystals to determine their size, shape, and orientation. If done carefully considerable detail about the ice structure can be determined.

Piece of relatively thin, vertical cross section a partly refrozen contraction crack between crossed polars. The ice sheet is 2.5" thick (the vertical axis of this picture).

 The picture above shows a moderately thin (0.1"?) slice of the cross section of a partially refrozen contraction crack.  The ice is between two crossed polarizing sheets. The colors show some details about the refreezing process and the how the ice sheet itself formed.  In this case the first thin layer was probably from snow falling into the water.  The ice underneath the surface is surface crystals that grew vertically downward.  With the right equipment, polarized light can be used to determine the direction of the crystal axies. 

  • Refractive Index:  The amount light slows down when it enters a material such as ice or water.  For ice the index of refraction for 580 nm wavelength (yellow color)  is 1.309 (C axis), water is 1.33 and, for reference, glass is 1.52. For example,  the speed of light in ice is about 3/4 its speed in a vacuum.  
  • Birefringence: The difference between the refractive index measured on the C axis and A axis. Many crystalline materials have different refractive indexes depending on what direction they are viewed.  Ice when viewed along the C axis, 590 nm (yellow-orange) light has a has a refractive index of 1.309 and when viewed on the A axis plane it is 1.313.  The difference between these two numbers is the birefringence magnitude. For ice it is +0.004. This is very low for birefringent materials.
  • Ice 1h:  One of 15 crystalline or amorphous structures of ice and the only form encountered in lake ice.  All the others occur at higher pressures and/or lower temperatures. No other substance has so many different solid state forms.
  • Ice Types:  there are several types of 1h ice of that are based on how the ice formed and how it grows from there. (more..)