Some Geographical Terms

Hadley Cell The Hadley cell is one of the parts of the global atmospheric circulation pattern of winds. This part or cell extends from the equator to about latitudes 30° N and S. In it, air, rises at the intertropical convergence zone (ITCZ) near the equator before flowing polewards at high altitudes. The cell is named after its inventor G. Hadley.

Hail Precipitation in the form of pellets of ice that develop in and fall from a cumulo-nimbus cloud is called hail. Hail is associated either with the passage of a cold front in temperate latitudes or with rapidly ascending convec­tion currents in low latitudes.

Hamada (Hammada) An Arabic term, hamada or hammada refers to an extensive flat rocky surface in desert from which sand has been removed by the wind. Hamadas are very frequent in the Sahara and Gobi deserts.

Hanging Valley A hanging valley is a tributary valley that lies above the main valley and is separated from it by a steep slope. A river flowing down the hanging valley descends to the main valley as a waterfall or series of rapids. Hanging valleys are more common in glaciated areas.

Hawaiian 'High' Located in Northern Pacific, the Hawaiian 'high' is one of the high-pressure cells in the atmospheric circulation. Such a cell is more pronounced in the northern summer than in the northern winter.

Haze The term haze refers to an obscurity of the lower atmosphere that limits visibility to under 2 km but over 1 km. It is normally formed by water particles that have condensed around nuclei in the atmosphere.

Heath An open uncultivated lowland area in temperate regions is called heath or heathland. Health usually contains podzol soils.

Heat Island The heat island refers to an urban area where temperatures tend to be higher than those of the surrounding countryside. Escaping heat from buildings, reflection and radiation from concrete, tarmac and bricks, and heat emitted by motor vehicles circulating in the urban area are among the causes for the phenomenon of heat island.

Hercynian Orogeny The term Hercynian orogeny refers to the mountain building episode of carboniferous/ Permian times.

Heterosphere The outer zone of the earth's atmosphere is called heterosphere. The gaseous constituents of the heterosphere exhibit very low densities.

Hiatus The hiatus refers to a gap in a stratigraphic sequence of rocks, where the missing strata were never deposited or were destroyed by erosion before deposition of the overlying strata.

Hinterland A hinterland is an area that has close economic, social and cultural ties with a central place, such as a port, city or town. In the case of a port, hinterland is the region from which it receives trade or to which it sends goods.

Homoseismal Line (Homoseism) Homoseismal line or homoseism is a line that connects all points of on a map that are affected simultaneously by an earthquake shock. It is synonymous with isoseist.

Homosphere Homosphere is the inner zone of the earth's atmosphere beneath the heterosphere. The gaseous constituents of the homosphere have higher densities.

Homotaxis Homotaxis refers to those rock strata which occupy the same position in the stratigraphic sequence, although they occur in different regions. Horse Latitudes Horse latitudes refer to the zones of high atmospheric pressure occurring over the oceans in latitudes about 30°-35° Nand 30°-35° 5, i.e, between the belts of the trade winds and the westerlies. They are zones of mainly descending air and are characterised by comparatively dry and stable conditions.

Horst A horst is an elevated block of rock bounded by faults. It has been left upstanding by the sinking of the adjoining land along normal faults or has been uplifted along parallel faults.

Hot Spring (Thermal Spring) Hot spring is a thermal spring that flows out. of the ground with temperatures above 37° C. It is more common in areas of current or recently active vulcanicity, though it is also found in non-volcanic areas. Unlike a geyser, water in a hot spring flows continuously instead of intermittently.

Hum A hum is an isolated hill left as a residual on the floor of a polje. It is named from the village of Hum in the Yugoslavian Karst.

Humidity Humidity is the state of the atmosphere in relation to its water vapour content. It normally refers to relative humidity unless otherwise stated.

Humus Humus is a black or dark-brown organic substaI which is produced by the process of mineralisation a humification within the soil. The formation of hurr requires aerobic conditions in soils. Humus increases s
fertility by providing essential nutrients such as nitrog and trace elements.

Hurricane Hurricane, a term of Spanish derivation, refl primarily to tropical storms of the Caribbean and G: of Mexico. It is accompanied by torrential rain, thunc and lightning. Hurricanes are most frequent in September and October.

Hydration Hydration is a weathering process in whi water is taken up by the mineral of a rock, caus considerable expansion of minerals.

Hydrograph A graph that shows the variation in the lev, velocity or discharge of a body of water with time known as hydrograph.

Hydrosphere The term hydrosphere refers to the tot water surrounding the earth. It includes surface wat oceans, seas, lakes, rivers, ice caps, atmospheric wat and water below the earth's surface.

Hygrograph Hydrograph is an instrument which recon the changing relative humidity of the atmosphere. The most common type is the hair hydrograph.

Hygrometer Hygrometer is an instrument which mea sun the relative humidity of the atmosphere at any pob in time.

Hygroscopic Nuclei Hygroscopic nuclei refer to particuler of dust, smoke, sulphur dioxide, salts or similar micn scopic substances occurring in the atmosphere aroun which condensation occurs. Condensation commenCE on hygroscopic nuclei before the air is saturated.

Hypsometer Hypsometer is an instrument that is used the determination of altitude or atmospheric pressur by measuring the temperature at which water boils