1. types of ice. basic ice physics

8/11/2019 1. Types of Ice. Basic Ice Physics

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Formation of ice

The addition of salt lowers both the temperature of maximum

density and, to a lesser extent, that of freezing

Further cooling results in expansion.

The maximum density of fresh water occurs at a temperature

of 4.0

C, and freezing takes place at 0

C


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Tempe

ratureC

Salinity


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Ice will begin forming at the watersurface when density currents

cease and the surface water

reaches its freezing point. In shoalwater, however, the mixing process

can be sufficient to extend the

freezing temperature from surface

to the bottom.


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Thickness of sea ice

2 meters during its first year (if no deformation);

3.5 -

4.5 meters in coastal areas.


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The growth of sea ice depends on:

Air temperature;

Initial ice thickness;

Snow depth;

Wind speed;

Seawater salinity and density;

Specific heats of sea ice and seawater.


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Zubovs formula

h

+ 50h = 8

h

ice thickness in cm for a given

day;

is the cumulative number of frost

degree days in C

since the beginningof the freezing season


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Land ice


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Land ice is formed on land by the freezing

of freshwater or the compacting of snow aslayer upon layer adds to the pressure on

that beneath.


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Ice cap

If a large area is relatively flat, or if the outward flow is

obstructed, an ice cap

forms and remains essentially

permanent.


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Under great pressure,

ice becomes slightly

plastic, and is forceddownward along and

inclined surface.

Where ravines ormountains passes

permit flow of the ice,

a glacier

is formed.

Glacier


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Iceberg

When a glacier reaches a comparatively level area, it

spreads out. When a glacier flows into the sea, the buoyant

force of the water breaks off pieces from time to time, andthese float away as icebergs.


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Types of icebergs

Dome shaped

Pinnacled

Tabular

Weathered


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Bergy bit

A relatively large piece of floating ice, generally extending

1 to 5 meters above the sea surface and normally about

100 to 300 square meters in area, is called a bergy bit.


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Growler

A smaller piece of ice, extending less than 1 meter above

the sea surface and occupying an area of about 20 m

iscalled a growler.


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Rams

Another danger is from underwater extensions, called

rams,

which are usually formed due to melting or

erosion above the waterline at a faster rate than below.


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Ice front

Ice front

forms the seaward face of a massive ice sheet

or floating glacier.


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Ice wall

Ice wall, which is the ice cliff forming the seaward

margin of a glacier which is aground.


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Sea ice


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Sea ice forms by the freezing of seawater

and accounts for 95% of all ice encountered


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Frazil ice

The first indication of formation of sea ice is frazil ice(small, individual crystals of ice)


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Grease ice

Grease ice

is formed when the ice crystals coagulate to

form a soupy layer on the surface, giving the sea a matteappearance


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Shuga

Shuga

is an accumulation of spongy white ice lumps

developing from grease ice.


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Nilas

Upon further freezing grease ice and shuga will develop

into nilas, an elastic crust of high salinity with a mattesurface, or


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Ice rind

into ice rind, a brittle, shiny crust of low salinity


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Pancake ice

When new ice becomes older, thicker, more brittle and

exposed to the influence of wind and wave action,separated circular pieces of ice or pancake ice

develops.


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Ice cake

Any single piece of flat sea ice less than 20m across is

called an ice cake


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Ice floe

With continued low temperatures, individual ice cakes and

pancake ice either freeze together, forming a continuous

sheet or unite into pieces of ice 20 m or more across. Theseare called ice floes.


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Ice field

Ice floes may further freeze together to form an ice

covered area greater than 10km across known as an ice

field


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Young ice

When sea ice reaches a thickness of between 10 to 30 cm

it is referred as young ice, and is the transition stagebetween nilas and first-year ice


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First-year ice

First-year

ice usually attains a thickness of between

30 cm and 2 m in its first winters growth


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Multiyear ice

Old ice which has attained a thickness of 3m or more and

has survived at least two summers

melt is calledmultiyear ice and is almost salt free.


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Ice concentrations:

Open water

(total concentration of all ice is less than 1/10);

Very open pack

(1-3 tenths concentration);

Open pack


Close pack


Very close pack

(9-10 to 10-10 concentration);

Compact or consolidated pack

(100% coverage).


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Fresh water ice


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Fresh water ice

New fresh water ice -

< 5 cm;

Thin fresh water ice -

5-15 cm;

Medium fresh water ice -

15-30 cm;

Thick fresh water ice -

30-70 cm;Very thick fresh water ice -

> 70 cm.

A brief note on the formation of sea ice


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A brief note on the formation of sea ice.

Sea water freezes at about -

2

C, Depending on

salinity. At certain stage of freezing brine is

trapped in small pockets in ice. At this stage this

newly formed ice is relatively soft and pliable

Melting and disintegration of sea ice


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Melting and disintegration of sea ice.

The process of melting and disintegration of sea ice is

more complex than its formation and growth, and will

depend on the salt content and age of the ice.



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Puddles or pools

As summer progresses, surface of the ice and the

snow cover melt forming puddles or pools of fresh ornearly fresh water, and these increase steadily in size.



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Thaw holes

The puddles absorb more radiation from the sun than

the adjoining ice surface and develop into thaw holes

through the ice. This results in the gradual break up ofthe ice.



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Honeycombed appearance of some of the forms of sea

ice in the final stages of melting and disintegration.


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Glacier ice (ice originating from glaciers).


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A note on the stability of icebergs.


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y g

Due to continuous process of erosion and melting, particularly

of the submerged portion, the shape of an iceberg is

continually changing. When the iceberg becomes top heavy

and G and B move to G

and B, The iceberg will capsize.

A note on the stability of icebergs.


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y g

After capsizing, G and B assume new locations G

and Band the process will continue until the iceberg completely

melts or disintegrates reaching warmer waters.


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Wherever there are ice bergs, there may also be growlers

or other ice debris which break away from ice bergs and

usually drift downwind, and which should be avoided.

Normally they should be passed to windward.


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Pass to windward if possible

Pack ice any accumulation of sea ice other


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y

than fast ice.

Open water

Concentration:

0 to 1/10


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Very open pack

Concentration:

1/10 to 3/10


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Open pack

Concentration:

4/10 to 6/10


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Close pack

Concentration:

7/10 to 9/10


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Very close pack

Consolidated pack: 10/10

(Floes frozen together)

Compact pack 10/10

(No water visible)

A floe a relatively flat piece of floating ice.


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Small floes

20 to 100 m across


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Medium floes

100 to 500 m across


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Big floes

500 to 2 km across


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Vast floes

2 to 10 km across


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Giant floes

over 10 km across

Other ice terms in general use.


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Ice cake

Floes are smaller

than 20 m across


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Brash ice

Fragments of ice not

more than 2 m across


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Pancake ice

New ice,

approximately

circular, about 0.3 m

to 3.0 m across

Ice ridge.


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Keels may extend as much as 50 m below sea level


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Rafted ice.


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Common in newly formed sea ice

Ice strips.


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A long narrow area of pack ice about 1 km or less in

width composed of small fragments of ice

Ice patch.


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An area of pack ice less than 10 km across

Floeberg.


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A floeberg is a massive piece of sea ice composed of

hummocked ice frozen together, thickness up to 5 mabove sea level


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Pressure in ice.


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Due to wind action the open pack now becomes very close

pack or consolidated or compact pack with ice hummocking

and ridging, and floes freezing together. In this state it could

be impossible even by powerful icebreaker


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Ice detection by marine radar


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Types of ice on the

radar screen

1. types of ice. basic ice physics

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