Great Dividing Range

Great Dividing Range,

crest line of the Eastern Highlands of Australia. For the most part it separates rivers draining into the Pacific Ocean from those flowing into the Indian Ocean and the Arafura Sea.

Great Dividing Range

a mountain chain extending almost 4,000 km along the eastern and southeastern coast of Australia, from the Cape York Peninsula on the north to the Bass Strait on the south. The name “Great Dividing Range” sometimes applies only to the western chain in Queensland between 15° and 27° S lat.

The Great Dividing Range is a large vaulted elevation that arose in the Neocene-Anthropogenic epoch. The mountains are composed basically of Paleozoic and, to a lesser degree, Mesozoic rock. In geological terms the range corresponds to the Tasmanian Paleozoic fold region, whose southern and eastern parts are formed of structures of the Middle Paleozoic (Caledonian) Lachlan fold system, and the central and northwest parts are structures of the Upper Paleozoic (Hercynian) New England fold system. Within the bounds of the Lachlan fold system, the most widely distributed rocks are dislocated sedimentary and volcanic rocks of the Ordovician, Silurian, and Lower and Middle Devonian periods, irrupted with granite and covered over with slanting Upper Paleozoic and Mesozoic deposits. On the west and northwest, within the New England range’s bounds, are widely distributed rocks of the Devonian, Carboniferous, and Permian periods, dislocated in late Permian times and irrupted by granite and ultrabasic intrusions. These fold forms are buried under Mesozoic sinks. In the middle portion of the ridge (from Sydney on the south to Rockhampton on the north), between the Lachlan and New England systems, is the Sydney-Bowen marginal trough, composed of continental and marine rock of the Upper Permian and Triassic periods. To the northwest and south of the highland are Paleozoic and Mesozoic rock covered with Neocene plateau basalts. In the central part of the range, in the Mesozoic deposits of the Sydney-Bowen trough, there are deposits of oil and gas (Roma); on the western slope there are tin (Mount Garnet), polymetals (Herberton), gold (Charters Towers), copper (Mount Morgan), and titanium-magnetite and monacite sands (Byron Bay and Ballina). In the environs of Newcastle and Wollongong is Australia’s largest coal basin, and east of Melbourne there is lignite.

North of 28° S lat., the Great Dividing Range reaches a width of 650 km and consists of coastal tablelands and massifs averaging about 1,000 m in elevation, central tectonicerosional hollows, and a western mountain chain, badly expressed in relief, 500–700 m in elevation, which divides rivers flowing into the Coral Sea, the Gulf of Carpentaria, the Indian Ocean, and the basin of Lake Eyre. The displacement of the water divide of the western high coastal massifs is a result of Anthropogenic rises causing deep erosion. The rivers intersected the previous divide and intercepted the flow of ancient rivers flowing to the west. South of 28° S lat. the Great Dividing Range is a narrow chain of individual massifs; from north to south in this terrain are the crystalline New England range, the latitudinal Hastings and Liverpool ranges framing it on the south, the limestone Blue Mountains, and the Australian Alps, a crystalline upland with the highest peaks in Australia (including Mount Kosciusko, 2,230 m). On the southeast the Great Dividing Range extends from the east to the west along latitudinal fractures that separate the island of Tasmania from the continent.

The Great Dividing Range lies in subequatorial (north of 15° S lat.), tropical (between 15° and 28° S lat.), and subtropical (south of 28° S lat.) belts. The landscapes of the windward eastern and leeward western slopes are sharply different in all belts. Moist winds from the Pacific Ocean bring the eastern slopes between 1,000 and 2,000 mm of precipitation annually, with a summer maximum (except in the south, where the maxima are in the winter). The western slopes are drier (500–700 mm annually). The average monthly temperatures decrease from north to south (on the coast, from 26° to 21° C in the summer and from 17° to 10° C in the winter), and in the mountains they decrease with increasing elevation. Snow covers the ground for five to six months in the Australian Alps.

Short rivers that are full of rapids but are deep—some of which are navigable in their lower courses (such as the Burdekin, Fitzroy, and Hunter rivers) flow from the Great Dividing Range to the Coral and Tasman seas. The Murray and Darling rivers, as well as the episodic creeks of interior Australia, begin on the western slopes.

The eastern slopes are forested. Up to an elevation of 1,000 m, north of 15° S lat., there are deciduous-evergreen rain forests; from 15° to 28° S lat. there are tropical eucalyptus forests; and further south there are subtropical monsoon forests of tall-trunk eucalyptus. In the Australian Alps there are dwarfed and stunted mountain forests from 1,000 to 1,600–2,000 m; higher, there are high-mountain meadows. On the drier western slopes of the Great Dividing Range there are forest savannas, savannas, and thickets of xerophytic shrubs. In the forests of the Great Dividing Range there are such animals as the koala, cuscus, and tree kangaroo; such birds as the bird of paradise, lyrebird, cassowary, and parrot are characteristic. The Australian lungfish still exists in the rivers.

N. A. BOGDANOV (geological sketch) and L. G. FROLOVA

Great Dividing Range