Australia's Great Basin

The Lake Eyre Basin of east-central Australia is a vast topographic bowl within which streams drain toward the lowest part of the basin, never reaching the sea.  Covering 440,000 square miles from southwestern Queensland to South Australia and from the southeastern corner of the Northern Territory to the northwestern edge of New South Wales, most of it is dry, desert landscape through which ephemeral streams lead to Lake Eyre, in the southwest corner of the Basin.  Nearly dry and coated with salt flats most of the time, the lake fills only twice each Century (on average); composed of a large northern basin connected to a smaller southern basin by the Goyder Channel, Lake Eyre covers 3700 square miles and has an average depth of less than 10 feet (when full)  The lowest point of the lake basin, in Belt Bay of the northern portion, is 50 feet below sea level while the rim of the lake is 30 feet below the level of the sea.

The Lake Eyre Basin began to form about 200 million years ago, when Australia was part of Gondwanaland.  Tectonic forces caused the crust of this region to subside and, within another 100 million years, an arm of the sea invaded the basin; when uplift occurred along the northern and eastern margins of the basin, the sea drained away and rivers flowed across the region, depositing sediments on their way to the ocean.  During the middle of the Pleistocene, about 1 million years ago, uplift along the southern rim closed off the basin and all streams fed Lake Diers, the much larger predecessor of Lake Eyre (as Lake Bonneville preceded the Great Salt Lake in the U.S.).  As the climate became warmer and drier late in the Pleistocene and into the Holocene, the flow through the rivers diminished and eventually became sporadic.  Today, what little water reaches the lake is via three primary river systems: the Georgina River from the north, the Diamantia River from the northeast and Cooper Creek from the east.  Most streams from the west and northwest dry up before reaching Lake Eyre.

During those rare periods when monsoon rains or tropical storms fill Lake Eyre, this remote oasis attracts huge flocks of shorebirds, terns and Australian Pelicans that nest on the islands and feed in the shallows; how these birds know that the distant lake is full remains a mystery.  Lake Eyre National Park stretches along the east shore of the northern lake, just a short 435 mile drive north from Adelaide.  Major towns within the Lake Eyre Basin include Alice Springs, Mt. Isa, Longreach and Broken Hill.

Geology of Australia's Blue Mountains

The beautiful city of Sydney, Australia, sits on a thick slab of Triassic Hawkesbury sandstone, some 200 million years old. Below this bedrock are older Triassic sediments, shales, mudstones and conglomerates of the Narrabeen Group. All of these deposits, swept into the Sydney Basin by ancient rivers, lie atop Permian strata; containing seams of coal, these latter rocks were emplaced about 250 million years ago, when Earth's land masses had merged into the mega-continent of Pangea.

Just west of the Sydney metropolitan area are the scenic Blue Mountains, a broad, dissected plateau that rose during the Jurassic Period, some 170 million years ago, when Australia was still part of Gondwanaland. The geologic strata of the plateau is identical to the bedrock below Sydney; Triassic sandstone, capped at high points by Miocene basalt, forms massive cliffs which sit atop the older Narrabeen Group and underlying Permian deposits. Metamorphosed Paleozoic rock, from the Silurian and Devonian Periods, lies at the base of the Mountains.

As this elongated block of crust warped upward, vertical fractures developed in the sandstone cap, setting the stage for magnificent canyons to erode through the plateau as streams and rock falls gradually widened the gaps. Now home to a spectacular diversity of plant and animal life, much of the plateau, a component of the Great Dividing Range and named for the blue haze produced by its eucalytus forests, is protected as a World Heritage Area.

A Message from Christchurch

Today's tragic earthquake, in Christchurch, New Zealand, is just the latest reminder that the surface of the Earth continues to evolve and that we who live upon its moving plates are potential victims of the tectonic forces that mold our planet. Those of us who reside along the active margins of these plates, where collision or subduction are occuring, are at the greatest risk of earthquakes but the presence of old suture lines, aborted rifts and buried faults within the interior of continental plates make us all susceptible to some degree.

Active zones of volcanism and earthquakes are spaced along the Pacific Rim, popularly known as the Ring of Fire. In most of these areas, the Pacific Plate and its smaller associated plates are subducting beneath the South American, North American, Eurasian and Australian Plates, producing volcanic mountain ranges and triggering earthquakes that eminate from both the oceanic trenches and the rising peaks; the Andes, the Mexican Volcanic Belt, the Cascades, the Aleutians, the Japanese Islands, Taiwan, the Philippines, and the North Island of New Zealand have all formed (and continue to form)in this manner.

On the South Island of New Zealand, the Australian and Pacific Plates are colliding and scraping against one another, forcing up the scenic mountains of that island and setting the stage for catastrophic earthquakes. Today's quake, measuring 6.3 on the Richter scale, is thought to be an aftershock from the 7.1 quake last September; unfortunately, this one was both shallow (less than 3 miles deep) and close to Christchurch, resulting in extensive damage and at least 65 deaths. The message is clear: devastating quakes have and will continue to affect major urban centers across the globe as our planet evolves beneath our feet.

La Nina & the Australian Floods

The massive flooding across eastern Australia, which began in November, has been associated with the La Nina phenomenon, which tends to peak every 3 to 7 years. Produced by high pressure over the eastern Pacific and low pressure over the western Pacific, this weather pattern results in strong Pacific trade winds, which bring relatively warm ocean waters to the southeast coast of Asia and the northeast coast of Australia. This spawns strong cyclones and excessive rainfall in these areas, generally during an autumn to autumn cycle in the Southern Hemisphere.

Coinciding with a high Southern Oscillation Index, which measures the seasonal variance of sea surface pressure between Tahiti and Darwin, La Nina episodes trigger excessive precipitation across northern and eastern Australia. This year's flooding has been especially severe, disrupting transportation, stranding inland towns, inundating coal mines and wiping out much of the region's wheat crop. The Great Barrier Reef may also be affected, as plumes from the rivers of northeast Australia sweep particulates and pollutants toward that fragile ecosystem.

The current Australian flooding may prove to be the worst in recorded history. Unfortunately, some climatologists project that the La Nina and the opposite El Nino patterns will intensify with the advance of global warming. For eastern Australia, that could mean an alternating pattern of severe floods and prolonged drought.