Some Terms of Geography

Iceberg A large mass of ice floating in the sea is callel iceberg. Icebetgs are formed when blocks of ice breai away from an ice-shelf or a glacier. They are mos
frequent in Greenland and Antarctica.

Ice-Cap A permanent and often isolated mass of ice, which is smaller than an ice-sheet or an ice-field, is called ice cap.

Icelandic Low The term Icelandic low refers to a temporar) area of low pressure in the subpolar region of the Nortt Atlantic between Greenland and Iceland. Icelandic lov. is more chc1racteristic of the winter months than thosE of the summer.
Igneous Rocks Igneous rocks are the rocks that have formed from the crystallisation and solidification magma. They include hypabyssal, plutonic, pyroclastic and volcanic rocks, and are classified according to their feldspar character, grain size, texture and chemical composition.

Inceptisol Inceptisol refers to very youthful soils whose poorly developed horizons have developed quickly on newly exposed surfaces. Inceptisol soils lack many
important materials such as iron or aluminium.

Indian Summer,Indian summer refers to a period of mild and sunny weather commonly occurring between late October and mid-November, Le., after the summer season has ended, in the USA. In the UK, it occurs in early September.

Inselberg The term inselberg is used to describe a promi­nent steep-sided mass of solid rock, which rises abruptly from a plain of low relief. Inselberg is characteristic of tropical landscapes, particularly in the Savannah zone and is generally composed of a resistant rock, such as a granite.

Insolation Insolation is defined as the amount of diffuse and direct solar radiation that reaches the earth's sur­face. In other words, it is the radiant energy that reaches the earth from the sun. The amount of radiation reaching the earth varies from region to region.

Its annual amount is 2.5 times greater at the equator than at the poles. Thus insolation plays an important role in distinguishing different climatic zones. Radiant energy is discharged from the sun in different forms: (i) very short length rays (x-rays, gamma rays and ultra violet rays); (ii) visible light-rays; and (iii) infrared rays (of short wavelength).

Intensity of Rainfall A measure of the rate at which rain falls is termed as intensity of rainfall, which is expressed in terms of rainfall amount related to specific time period. The equation for intensity of rainfall is total rainfall/number of rainfall hours.

International Date Line International date line refers to an internationally agreed time-change line drawn approxi­mately along the 180" meridian. The line slightly devi­ates to both west and east to avoid land masses and groups of islands. The date immediately east of the line is one day earlier than to the west.

Intertropical Convergence Zone OTCZ) Intertropical con­vergence zone (ITCZ) refers to a broad zone of rela­tively low atmospheric pressure between northeast and south-east trade winds, i.e., in equatorial latitudes. It is also the meeting place of northern and southern tropicai maritime air masses. ITCZ tends to move North and South with the seasonal movement of the overhead sun. It is sharply defined over land than over oceans.

Inversion of Temperature Increase in temperature with height in the atmosphere is called inversion of tempera­ture (Normally air temperature decreases with increas­ing elevation). There are two types of inversion: (i) high­altitude inversion due to frontal convergence, and (ii) surface inversion due to rapid heat loss from the ground by radiation. Temperature inversions are most marked in basins, hollows and narrow valleys.

Ionosphere Ionosphere is the layer of atmosphere above the mesopause, beyond about 80 km above earth's surface. In this layer, incoming solar radiation ionises the gases within it forming ionised layer. Ionosphere reflects radio signals and other electromagnetic waves back to the earth.

Island An area of land completely surrounded by water is called island. Greenland, with an area of about 2.2. million km3, is the world's largest island.
Isostasy Isostasy refers to the principle that variations in