Geology Reference
In-Depth Information
Table 4.1
Categories and subcategories of freshwater and seawater ice types following the adaption with small changes of the
classification of
Michel and Ramseier
[1971]
.
Category
Subcategory
Description
Primary ice
P1
Calm ice surface with small temperature gradient
: Grain large to very large (can be giant
more than 1 m dimension) with irregular boundaries. Crystallographic orientation of
c
axis is preferred vertical. Found only in calm water.
P2
Calm ice surface with large temperature gradient
: Grain size medium to very large.
Crystallization progresses rapidly. Grain shape varies from tabular to needle‐like and can
be several centimeters in length. Crystallographic orientation is random or vertically
preferred (freshwater ice only) superimposed on a random orientation. Dendrites are
common.
P3
Agitated surface nucleated from frazil
: Grains are fine to medium with tabular shape.
Crystallographic orientation is random.
P4
Nucleation by snow
: Grains are fine to medium and equiaxed, depending on snow type.
Crystallographic orientation is random.
Secondary ice
S1
Columnar ice, preferred vertical
c
axis
: Grains are perpendicular to the ice cover surface.
Size increases with depth. Orientation of some crystals is preferred (natural selection
growth). Grain size ranges from large to very large with irregular boundaries. Forms as
a result of conditions given for P1 or P2 ice. Found in bodies of fresh water with low
velocity. S1 type of ice is not sustainable in sea ice except for a thin layer, a few mm in
thickness, at the top surface.
S2
Columnar ice, preferred horizontal
c
axis but random
: Conditions are the same as for S1 but
primary ice has a random orientation. Cross‐sectional (normal to long axis of the columns)
grain size ranges from fine to large with irregular boundaries. Grain size increases more
rapidly with depth than S1. Forms as a result of conditions given for P2, P3, and P4 types.
This type is isotropic in horizontal plane, but it is columnar vertically. In material science
this type of crystalline structure is known as traversal isotropic or orthotropic. S2 type
columnar-grained material is also known as 'Directionally solidified' (DS) in the field of
gas-turbine engine materials.
S3
Columnar ice, preferred aligned horizontal
c
axis
: Forms at the bottom of thick freshwater
lake ice sheet. In case of sea water, S3 type of ice is very common in areas with water
current.
S4
Congealed frazil slush
: Frazil is formed in turbulent water and is swept under the secondary
ice cover. Grains are equiaxed and tabular with fine to medium size. Crystal boundaries
are irregular and crystallographic orientation is random. Found in turbulent seawater.
S5
Typically vertically oriented needle‐shaped crystals:
Created in turbulent water, frazil crystals
are aligned and compacted by wave actions.
Superimposed
(Tertiary) ice
T1
Snow ice
: Rounded to angular equiaxed grains with fine to medium size depending on the age
of the snow. Formed when water saturates the snow deposited on ice surface, then freezes.
T2
Drained snow ice
: Randomly oriented but homogeneous rounded grains with fine to
medium size rounded. Found where water level vary, thus draining a previously saturated
snow that then freezes.
T3
Surface ice
: Layers of columnar ice formed on top of primary ice.
Random
R
Agglomeration of various ice types and forms
. Ice growth process is disturbed by
mechanical or other interference. Grain size varies from fine to very large. Crystal
boundaries regular to angular and orientation can be random to preferred.
Glacier ice
Land‐based ice masses
: The origin of icebergs, bergybits, and the massive ice islands. Form
as a result of snow deposition, compaction, and melting and freezing over hundreds of
thousands of years.
Notes
: Within each one of the above classes there are subclasses. Fine, medium, large, and very large grain size refer to
diameters < 1 mm, between 1 and 5 mm, between 5 and 20 mm, and > 20 mm, respectively. Superimposed ice always forms
on top of the primary ice and is caused by flooding of an ice cover from any possible water source (e.g., rain, freezing rain, or
snowfall). If the snow melts or become wet then freezes on the ice surface, then snow ice may form. An addition of oriented
frazil ice, type S5, is suggested for inclusion in the above table. It was not part of the original classification by
Michel and
Ramseier
[1971].
