The Werribee Plain is an expansive low-lying flat land located between the northwestern shore of

Port Phillip Bay Port Phillip (Kulin: ''Narm-Narm'') or Port Phillip Bay is a horsehead-shaped enclosed bay on the central coast of southern Victoria, Australia. The bay opens into the Bass Strait via a short, narrow channel known as The Rip, and is completel ...

and the

Grampians The Grampian Mountains (''Am Monadh'' in Scottish Gaelic, Gaelic) is one of the three major mountain ranges in Scotland, that together occupy about half of Scotland. The other two ranges are the Northwest Highlands and the Southern Uplands. T ...

Central Highlands of

Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seychelle ...

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

, shared between

Melbourne Melbourne ( ; Boonwurrung/Woiwurrung: ''Narrm'' or ''Naarm'') is the capital and most populous city of the Australian state of Victoria, and the second-most populous city in both Australia and Oceania. Its name generally refers to a met ...

and

Geelong Geelong ( ) (Wathawurrung: ''Djilang''/''Djalang'') is a port city in the southeastern Australian state of Victoria, located at the eastern end of Corio Bay (the smaller western portion of Port Phillip Bay) and the left bank of Barwon River, ...

. Named after the

Werribee River The Werribee River is a perennial river of the Port Phillip catchment that is located on the Werribee Plain, expansive lowland plain southwest of Melbourne, Victoria (Australia), Victoria, Australia. The headwaters of a tributary, the Lerderderg ...

, the plains are notable for their extensive, flat and rather featureless spans, interspersed by the occasional vertical feature, such as the

You Yangs The You Yangs are a series of granite ridges that rise up to above the flat and low-lying Werribee Plain in southern Victoria, Australia, approximately due west of the rural town of Little River, southwest of Melbourne CBD and north of Ge ...

, a series of

granite Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...

ridge A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for an extended distance. The sides of the ridge slope away from the narrow top on either side. The line ...

s and several small

extinct volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are ...

es. The Werribee Plain forms the eastern bayside portion of the vast Western Volcanic Plains between the

and the

Otway Ranges The Great Otway National Park is a national park located in the Barwon South West region of Victoria, Australia. The national park is situated approximately southwest of Melbourne, in the Otway Ranges, a low coastal mountain range. It conta ...

, which extend from the western suburbs of Melbourne to the

South Australia South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...

n border.

Geology

Volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are ...

es began erupting lava flows about 4.5 million years ago, and the youngest eruptions are only about 10,000 years old. There are over 400 mapped craters and vents on the plains. While all these individual volcanoes are extinct, the volcanic field itself is only dormant, so new eruptions are possible at any time. The granite that forms the

was originally a mass of

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

that worked its way up into the surrounding

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

s during a period of geological time known as the

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

. The

crystallised before it reached the surface, so it did not produce any volcanic activity. Instead, a very slow cooling rate allowed many large white crystals of feldspar to form. These can be seen in many of the granite outcrops throughout the ranges. The nearest volcanoes to the You Yangs are the Anakies, which appear as three low hills on the western horizon. These all have summit craters and provided lava flows for the plains south of the You Yangs. There were also flows from the low volcanoes of Bald Hill and Spring Hill to the north of the You Yangs. When these volcanoes were active, probably between 2 and 3 million years ago, the You Yangs would have been granite islands in a sea of lava.

References

{{coord missing, Victoria (state) Landforms of Victoria (state) Plains of Australia Werribee, Victoria