Bass Strait


Bass Strait is a strait separating the island state of Tasmania from the Australian mainland. The strait provides the most direct waterway between the Great Australian Bight and the Tasman Sea, and is also the only maritime route into the economically prominent Port Phillip Bay.
Formed 8,000 years ago by rising sea levels at the end of the last glacial period, the strait was named after English explorer and physician George Bass by European colonists.

Extent

The International Hydrographic Organization defines the limits of Bass Strait as follows:

Differing views of location and context

Some authorities consider the strait to be part of the Pacific Ocean as in the never-approved 2002 IHO Limits of Oceans and Seas draft. In the currently in-force IHO 1953 draft, it is instead associated with the Great Australian Bight; the Bight is numbered 62, while the Bass Strait is designated 62-A.
The Australian Hydrographic Service does not consider it to be part of its expanded definition of the Southern Ocean, but rather states that it lies with the Tasman Sea. The strait between the Furneaux Islands and Tasmania is Banks Strait, a subdivision of Bass Strait.

Discovery and exploration

By Aboriginal peoples

arrived in Tasmania approximately 40,000 years ago during the last glacial period, across a broad prehistoric land bridge called the Bassian Plain between the nowaday southern Victoria coastline and the northern Tasmanian shores. After the glacial period ended, sea levels rose and flooded the Bassian Plain to form Bass Strait at around 8,000 years ago, leaving them isolated from the Australian mainland. Aboriginal people lived on Flinders Island until around 4,000 years ago.
Based on the recorded language groups, there were at least three successive waves of Aboriginal colonisation.

By Europeans

The strait was possibly detected by Captain Abel Tasman when he charted Tasmania's coast in 1642. On 5 December Tasman was following the east coast northward to see how far it went. When the land veered to the north-west at Eddystone Point, he tried to keep in with it but his ships were suddenly hit by the Roaring Forties howling through Bass Strait. Tasman was on a mission to find the Southern Continent, not more islands, so he abruptly turned away to the east and continued his continent hunting.
The next European to approach the strait was Captain James Cook in HMS Endeavour in April 1770. However, after sailing for two hours westward towards the strait against the wind, he turned back east and noted in his journal that he was "doubtful whether they are one land or no".
The strait was named after George Bass, after he and Matthew Flinders sailed across it while circumnavigating Van Diemen's Land in the Norfolk in 1798–99. At Flinders' recommendation, the Governor of New South Wales, John Hunter, in 1800 named the stretch of water between the mainland and Van Diemen's Land "Bass's Straits". In 1798 it became known as Bass Strait.
The existence of the strait had been suggested in 1797 by the master of Sydney Cove when he reached Sydney after deliberately grounding his foundering ship and being stranded on Preservation Island. He reported that the strong south westerly swell and the tides and currents suggested that the island was in a channel linking the Pacific and southern Indian Ocean. Governor Hunter thus wrote to Joseph Banks in August 1797 that it seemed certain a strait existed.
When news of the 1798 discovery of Bass Strait reached Europe, the French government despatched a reconnaissance expedition commanded by Nicolas Baudin. This prompted Governor King to send two vessels from Sydney to the island to establish a garrison at Hobart.

Maritime history

Strong currents between the Antarctic-driven southeast portions of the Indian Ocean and the Tasman Sea's Pacific Ocean waters provide a strait of powerful, wild storm waves. The shipwrecks on the Tasmanian and Victorian coastlines number in the hundreds, although stronger metal ships and modern marine navigation have greatly reduced the danger.
Many vessels, some quite large, have disappeared without a trace, or left scant evidence of their passing. Despite myths and legends of piracy, wrecking and alleged supernatural phenomena akin to those of the Bermuda Triangle, such disappearances can be invariably ascribed to treacherous combinations of wind and sea conditions, and the numerous semi-submerged rocks and reefs within the Straits.
Despite the strait's difficult waters, it provided a safer and less boisterous passage for ships on the route from Europe or India to Sydney in the early 19th century. The strait also saved on the voyage.

Geography

Bass Strait is approximately wide and long, with an average depth of. The widest opening is about between Cape Portland on the northeastern tip of Tasmania and Point Hicks on the Australian mainland. Bass Canyon, one of the largest submarine canyons in the world, is situated on the eastern periphery of the strait.
Jennings' study of the submarine topography of Bass Strait described the bathymetric Bass Basin, a shallow depression approximately wide and long in the centre of Bass Strait, a maximum depth is the channel between Inner Sister Island and Flinders Island, which navigation charts indicate reaches. Two underwater plateaus, the Bassian Rise and King Island Rise located on the eastern and western margins of Bass Strait, respectively, are composed of a basement of Paleozoic granite. These features form sills separating Bass Basin from the adjacent ocean basins. Associated with the less than -deep Bassian Rise is the Furneaux Islands, the largest of which is Flinders Island. The surface of the King Island Rise also occurs in water depths of less than, and includes the shallow Tail Bank at its northern margin as well as King Island itself. Subaqueous dunes and tidal current ridges cover approximately of the seabed in Bass Strait.
During Pleistocene, low sea level stands the central basin of Bass Strait was enclosed by raised sills forming a large shallow lake. This occurred during the last glacial maximum when the basin was completely isolated. Sea level rise during the marine transgression flooded the basin, forming a westward embayment from 11,800 BP to 8700 BP, and the basin rim was completely flooded by about 8000 BP, at which point Bass Strait was formed and Tasmania became an isolated island.
Like the rest of the waters surrounding Tasmania, and particularly because of its limited depth, it is notoriously rough, with many ships lost there during the 19th century. A lighthouse was erected on Deal Island in 1848 to assist ships navigating in the eastern part of the Straits, but there were no guides to the western entrance until the Cape Otway Lighthouse was first lit in 1848, followed by another at Cape Wickham at the northern end of King Island in 1861.

Islands

There are over 50 islands in Bass Strait. Major islands include:
Western section:
South eastern section:
North eastern section:

Federal

Within Bass Strait there are several Commonwealth marine reserves, which are all part of the South-east Network. The two larger reserves, Flinders and Zeehan, extend mostly outside of the Bass Strait area.
The smaller islands of Bass Strait typically have some form of protection status. Most notably the Kent Group National Park covers the Kent Group islands of Tasmania, as well as the surrounding state waters which is a dedicated marine reserve. The national park is wholly contained by the Beagle Commonwealth Marine Reserve.
Victoria has several marine national parks in Bass Strait, and are all adjacent to the mainland coastline:
A number of oil and gas fields exist in the eastern portion of Bass Strait, in what is known as the Gippsland Basin. Most large fields were discovered in the 1960s, and are located about off the coast of Gippsland in water depths of about. These oil fields include the Halibut Field discovered in 1967, the Cobia Field discovered in 1972, the Kingfish Field, the Mackerel Field, and the Fortescue Field discovered in 1978. Large gas fields include the Whiptail field, the Barracouta Field, the Snapper Field, and the Marlin Field. Oil and gas are produced from the Cretaceous-Eocene clastic rocks of the Latrobe Group, deposited with the break-up of Australia and Antarctica. In 2020 activist group No Gas Across the Bass was set up after American company ConocoPhillips put in an application to seismic blast 27km from King Island. Further environmental campaigning followed the Australian government's 2020 Oil and Gas acreage release as this opened up new areas of Tasmania's oceans for exploration.
The western field, known as the Otway Basin, was discovered in the 1990s offshore near Port Campbell. Its exploitation began in 2005.
The oil and gas is sent via pipeline to gas processing facilities and oil refineries at Longford, Western Port, Altona and Geelong, as well as by tanker to New South Wales. Pipelines from the Otway Basin gas fields lead to several processing facilities in the vicinity of Port Campbell.
In June 2017, the Government of Victoria announced a three-year feasibility study for Australia's first offshore wind farm. The project, which could have 250 wind turbines within a area, is projected to deliver around 8,000 GWh of electricity, representing some 18 per cent of Victoria's power usage and replacing a large part of the output of Hazelwood Power Station, which was closed in early 2017.