Tweed Volcano is a partially eroded

Early Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene Epoch made up of two stages: the Aquitanian and Burdigalian stages. The sub-epoch lasted from 23.03 ± 0.05 Ma to 15.97 ± 0.05 Ma (million years ago). It was pr ...

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more vi ...

located in northeastern

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, which formed when this region of

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country b ...

passed over the East Australia hotspot around 23 million years ago. Mount Warning, Lamington Plateau and the Border Ranges between New South Wales and Queensland are among the remnants of this volcano that was originally over in

diameter In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid ...

and nearly twice the height of Mount Warning today, at . Despite its size, Tweed Volcano was not a

supervolcano A supervolcano is a volcano that has had an eruption with a Volcanic Explosivity Index (VEI) of 8, the largest recorded value on the index. This means the volume of deposits for such an eruption is greater than 1,000 cubic kilometers (240 cubi ...

; other shield volcanoes—such as in the

Hawaiian Islands The Hawaiian Islands ( haw, Nā Mokupuni o Hawai‘i) are an archipelago of eight major islands, several atolls, and numerous smaller islets in the North Pacific Ocean, extending some from the island of Hawaii in the south to northernmost K ...

—are much larger. In the 23 million years since the volcano was active, erosion has been extensive, forming a large

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is di ...

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

around the

volcanic plug A volcanic plug, also called a volcanic neck or lava neck, is a volcanic object created when magma hardens within a vent on an active volcano. When present, a plug can cause an extreme build-up of high gas pressure if rising volatile-charged ...

of Mount Warning. Its erosion caldera is the largest in the Southern Hemisphere.

Volcanic stratigraphy

Lavas from the Tweed Volcano are recognised as part of the Lamington Volcanics.Geoscience Australia Lamington Volcanics Stratigraphy
/ref> The volcanic

stratigraphy Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithostra ...

of the Tweed Volcano is similar to many other hotspot volcanoes around the world. Eruptions of

tholeiitic The tholeiitic magma series is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma ...

and some

calc-alkaline The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic ma ...

basalts are the oldest recognised units derived from the volcano. These are named the Lismore Basalt and Beechmont Basalt in

and

Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , established_ ...

respectively. There are numerous flows recorded which may have been erupted irregularly as fossil soil ( Paleosol) profiles and

lacustrine A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

type rock units are occasionally found within the rock unit. Following eruption of the Lismore/Beechmont Basalt a period of eruption of

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The m ...

lavas took place. Eruptions occurred in

lava Lava is molten or partially molten rock ( magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or ...

and some

pyroclastic Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...

forms. These rhyolites are known in New South Wales as the Nimbin Rhyolite and Queensland as the Binna Burra Rhyolite. Following eruption of this rhyolite a period of basaltic volcanism resumed (or continued) with the eruption of the Blue Knob (NSW)/Hobwee (QLD) Basalt. The erosion of the volcano has resulted in the exposure of the central feeders of the volcano. These are most evident as Mount Warning and Mount Nullum, though there are numerous other volcanic vents identified all around the region as far away as Nimbin in New South Wales and Spring Mount in Queensland. The central volcanic area in the vicinity of Mount Warning and Mount Nullum is known as the Mount Warning Central Complex and is composed of intrusive rocks including syenite, peralkaline granite, microgranite, monzonite, dolerite, as well as some hyperbassal and volcanic rocks such as rhyolite and basalt.

References

Mount Warning
* ttp://qld.gsa.org.au/oreillys.pdf Green Mountains, Lamington National Park

External links

Northern Rivers Geology Blog - Tweed Volcano
{{coord, 28, 23, 44.71, S, 153, 16, 0.19, E, display=title Tweed Shire

Volcanic stratigraphy

See also

References

External links