Which type of ice in the iceberg present ?

Question

Which type of ice in the iceberg present ?

Answer 1

Permanent Ice

Iceberg

I. Introduction

Iceberg, mass of freshwater ice that is calved, or broken off, from a glacier or an ice shelf (a huge slab of permanent ice that floats on water near the edges of polar land masses) and that floats in the ocean or in a lake. Ice floats because it is less dense than water. A typical iceberg shows only about one-fifth of its total mass above the water; the other four-fifths is submerged. Icebergs can be large. The largest iceberg ever sighted was 335 km (208 mi) long and 97 km (60 mi) wide, about the size of Belgium. It was sighted in November 1956 by the crew of a United States Coast Guard icebreaker in the Ross Sea, off Antarctica. Icebergs pose a hazard to shipping and to offshore activities, such as offshore oil drilling, in polar and subpolar waters.

Icebergs can have many different forms, depending on their origin and age. They are usually classified as tabular (resembling a flat tabletop), rounded, or irregular. From massive tabular icebergs calved from ice shelves to small irregular bergs that have been weathered and scoured by wind and waves, they present spectacular sights in the polar and subpolar seas.

Icebergs were known to early mariners and explorers and to sealers and whalers who hunted their prey in Arctic and Antarctic waters. Beginning in the 20th century, icebergs have been used as stable platforms for scientific stations. Some people have suggested towing icebergs to places where water is scarce and melting them there, but this idea has not yet been implemented.

II. Origin, Size, and Classification

As ice in coastal glaciers slides toward sea level, it eventually breaks off and falls into the ocean in various-sized pieces. The smallest pieces, which are football-size to table-size chunks less than 2 m (7 ft) in diameter, are called brash ice. Larger pieces that float low in the water are called growlers because waves washing over them produce a growling sound. Bergy bits are ice pieces between 2 and 5 m (7 and 16 ft) in diameter. All larger bodies of ice are called icebergs.

The largest icebergs come from ice shelves, which are the outer extensions of large icecaps and ice sheets, such as those located in Antarctica. (Icecaps are dome-shaped ice formations that are anchored on land and extend outward from an interior location, while ice sheets are flat extensions of icecaps and may cover both land and water.) Glaciers feeding into an icecap or ice sheet push the ice shelf out to sea. Ice shelves float on the ocean and can be 200 to 300 m (650 to 980 ft) thick. The pieces that eventually break off from ice shelves can form icebergs hundreds of kilometers long and tens of kilometers wide. These icebergs may weigh billions or even trillions of tons. Icebergs that break off from ice shelves are called tabular icebergs because their flat upper surface resembles a flat tabletop.

The icebergs that come from glaciers that flow to the sea are generally smaller than those from ice shelves. When the ice reaches the sea, pieces break off and fall into the water. The icebergs then drift away from the shore. Glaciers in Greenland and Alaska produce many such icebergs every year.

Icebergs are driven away from the shore by winds and ocean currents and slowly break up and melt. The smallest pieces disappear first, and the large tabular icebergs last the longest. On average, an iceberg lasts about four years, but many icebergs last much longer. Tabular icebergs often have spectacular caves in their sides, carved out by wave action. As an iceberg shrinks, it may tilt or roll over so that the smooth underside or lines etched out by the waves come into view. Icebergs transformed in this way often have fantastic shapes.

Each of the three major types of icebergs (tabular, rounded, and irregular) has numerous subcategories. Tabular icebergs show no signs of rollover and may be horizontal (totally flat), uneven, domed, tilted, or blocky. Rounded icebergs have been smoothed by the water and have rolled over. Irregular icebergs have angular or irregular features. Their shapes include pinnacled, pyramidal, drydock, castellated, jagged, blocky, roofed, and rounded. Drydock icebergs have a low sunken area in the middle that is often awash. The skylines of castellated icebergs resemble the battlements on a castle.