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ICE, BASICS

Q. Describe a water molecule.
Chemical formula of water is H2O. The hydrogen atoms are joined to the oxygen atom via covalent bonds. The oxygen atom has high electro negativity. It attracts the protons (positive poles) of hydrogen towards itself. The angle between oxygen and hydrogen in water molecule is 104.5o.

Q. Why the density of water is maximum at 40C?
The inter molecular force between molecules that make up a liquid determine its freezing point. Water molecules form hexagon shape in 3 dimensions. When temp. is lowered these hexagonal shapes tend to come closer causing  density of water to increase. At 4°c the closeness is maximum. Thereafter, the space that is created within hexagons no outer molecules can come in. The average energy of the molecules decreases. With the further removal of heat at 00C the attractive forces between molecules draw the molecules close together, and the liquid reaches a steady state at which density does not change and becomes solid.

Q. How is freezing temperature and maximum density of sea ice related?

Max density curve is straight line curve starting from 4°C. Freezing Point curve is straight line curve starting from 0°C. The maximum density curve and freezing point curves meet at –1.33°C at 24.7%o salinity. Diagrammatically, the relationship between temperature salinity and maximum density can be shown. It can be seen that in water with salinity of less than 24.7 the maximum density is reached before the freezing temperature and where the salinity is greater than 24.7 the freezing point is reached before the density attains its theoretical maximum value.

Q. What are the stages of formation of sea ice?
Freezing of saline water does not occur in the same manner as fresh water. This is due to dissolved salts in sea water. Sea water has a salinity of 35%0. The first indication of ice is the appearance of ice spicules or plates, with maximum dimension up to 2.5cm, in the top few cm of water. These spicules known as frazil ice, coalesces to form grease ice, which has mat appearance. Under near freezing, but still ice free conditions, snow falling on the surface and forming slush may induce the sea surface to form a layer of ice. These forms may breakup under the action of wind and waves to form shuga. Frazil ice, slush, shuga and grease ice are classified as new ice.

Q. What is Nilas?
With further cooling sheets of ice rind or nilas are formed depending on the rate of cooling and on the salinity of water. Ice rind is formed when water of low salinity freezes slowly resulting in a thin layer of ice which is almost free of salt, whereas; when water of high salinity freezes specially if process is rapid, the ice contains the pockets of salt water giving it an elastic property which is characteristic of nilas. The layer formed is subdivided according to age into dark and light nilas. Thickness is up to 10cm.

Q. What is Young ice?
The action of wind and waves may break ice rind and nilas into pancake ice which later freezes together and thickens into grey ice and grey white ice, the later attaining thickness up to 30cm. These forms of ice are called young ice. Rough weather may break this ice into cakes or floes.

Q. What is the difference between Grey Ice & Grey-White Ice?
Young ice 10-15 cm thick, less elastic than nilas and breaks on swell. It usually rafts under pressure. Young ice 15-30 cm thick. Under pressure it is more likely to ridge than to raft.

Q. What is First-year Ice?
Sea ice of not more than one winter’s growth, developing from young ice; 30 cm or greater. It may be subdivided into thin first-year ice – sometimes referred to as white ice -, medium first-year ice and thick first-year ice.

Q. What is 2nd year & Multi-year Ice?
Sea ice which has survived at least one summer’s melt. Topographic features generally are smoother than first-year ice. It may be subdivided into second-year ice and multi-year ice. Old ice which has survived only one summer’s melt. Thicker than first-year ice, it stands higher out of the water. In contrast to multi-year ice, summer melting produces a regular pattern of numerous small puddles. Bare patches and puddles are usually greenish-blue. Old ice which has survived at least two summer’s melt. Hummocks are smoother than on second-year ice and the ice is almost salt-free. Where bare, this ice is usually blue in colour. The melt pattern consists of large interconnecting, irregular puddles and a well-developed drainage system.

Q. What are the principal forms of glaciers?
The glaciers can be Inland ice sheets, ice shelves, ice streams, ice caps, ice piedmonts, cirque glaciers and various types of mountain (valley) glaciers.

Q. What is Glacier Tongue?
Glacier Tongue is the projecting seaward extension of a glacier. It is usually afloat.

Q. What is Iceberg Tongue?
It is a major accumulation of icebergs projecting from the coast. It is held in place by grounding and joined together by fast ice.

Q. What is Ice Shelf?
Ice shelf is a floating ice sheet of considerable thickness showing 2 m or more above sea level, attached to the coast. They usually have great horizontal extent and a level or gently undulating surface. Ice shelf growth occurs by annual snow accumulation and also by the seaward extension of land glaciers. Limited areas may be aground. The seaward edge is termed an ice front.

Q. What is Calving?
The breaking away of a mass of ice from an ice wall, ice front or iceberg is called calving.

Q. What is an iceberg?
It is a massive piece of ice of greatly varying shape, protruding 5 m or more above sea level, which has broken away from a glacier and which may be afloat or aground. They may be described as tabular, domed, pinnacled, wedged, dry docked or blocky. Sizes of icebergs are classed as small, medium, large and very large.

Q. What is a tabular iceberg?
It is a flat-topped iceberg. Most tabular icebergs show horizontal banding.

Q. What is a domed iceberg?
It is an iceberg which is smooth and rounded on top.

Q. What is a pinnacled iceberg?
It is an iceberg with a central spire or pyramid, with one or more spires.

Q. What is a wedged iceberg?
It is an iceberg which is rather flat on top and with steep vertical sides on one end, sloping to lesser sides on the other end.

Q. What is a drydocked iceberg?
It is an iceberg which is eroded such that a U-shaped slot is formed near or at water level, with twin columns or pinnacles.

Q. What is a blocky iceberg?
It is a flat-topped iceberg with steep vertical sides.

Q. What is a growler?
It is a piece of ice smaller than a bergy bit and floating less then 1 m above the sea surface, a growler generally appears white but sometimes transparent or blue-green in colour. Extending less than 1 m above the sea surface and normally occupying an area of about 20 sq.m., growlers are difficult to distinguish when surrounded by sea ice or in high sea state.

Q. What is a bergy bit?
It is a piece of glacier ice, generally showing 1m to less than 5 m above sea level, with a length of 5m to less than 15 m. They normally have an area of 100-300 sq. m.

Q. What is a small iceberg?
It is usually, a piece of glacier ice extending 5m to 15 m above sea level and with a length of 15m to 60 m.

Q. What is Pancake Ice?
It is formed by predominantly circular pieces of ice, 30 cm to 3 m in diameter, up to 10 cm in thickness, with raised rims due to the pieces striking against one another. It may form on a slight swell from grease ice, shuga or slush or as a result of the breaking of ice rind, nilas or, under severe conditions of swell or waves, of grey ice. It also sometimes forms at some depth at an interface between water bodies of different physical characteristics where it floats to the surface. It may rapidly form over wide areas of water.

Q. What are floes?
Floes are relatively flat pieces of ice 20 m or more across. Floes are subdivided according to horizontal extent as follows:
Small:  20-100 m across.
Medium: 100-500 m across.
Big: 500-2,000 m across.
Vast:  2-10 km across.
Giant: 2-10 km across.
Very Vast: Greater than 10 km across.

Q. What is Fast Ice?
Fast ice is the ice which forms and remains fast along the coast. It may be attached to the shore, to an ice wall, to an ice front, between shoals or grounded icebergs. Vertical fluctuations may be observed during changes of sea level. It may be formed “in-situ” from water or by freezing of floating ice of any age to shore and can extend a few metres or several hundred kilometres from the coast. It may be more than one year old in which case it may be prefixed with the appropriate age category (old, second-year or multi-year). If higher than 2 m above sea level, it is called an ice shelf.

Q. What is Compact Ice?
Compact ice is floating ice in which the concentration is 10/10 and no water is visible.

Q. What is very close pack/drift?
Floating ice in which the concentration is 9/10 to less than 10/10.

Q. What is close pack/drift?
Floating ice, in which the concentration is 7/10 to 8/10, composed of floes, mostly in contact with one another.

Q. What is open drift?
Floating ice in which the concentration is 4/10 to 6/10, with many leads is called open drift. Floes are generally not in contact with one another.

Q. What is very open drift?
Ice in which the concentration is 1/10 to 3/10 and thus water dominates over ice.

Q. What is open water?
A large area of freely navigable water in which ice is present in concentrations less than 1/10 is generally called open water. No ice of land origin is present.

Q. What is ice blink?
It is a whitish glare on low clouds above an accumulation of distant ice.

Q. What is beset?
Beset is a situation in which a vessel is surrounded by ice and the ship is unable to move.

Q. What is ice-bound?
A harbour, inlet, etc., is said to be ice-bound when navigation by ships is prevented, on account of ice, except possibly with the assistance of an icebreaker.

Q. What is nip?
Ice is said to nip when it forcibly presses against a ship. A vessel so caught, though undamaged, is said to have been nipped.

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