Tweed Volcano is a partially eroded

Early Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages: the Aquitanian age, Aquitanian and Burdigalian stages. The sub-epoch lasted from 23.03 ± 0.05 annum, Ma to ...

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a 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 viscous lava ...

located in northeastern

New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

, which formed when this region of

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

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 centre of the circle and whose endpoints lie on the circle. It can also be defined as the longest Chord (geometry), chord of the circle. Both definitions a ...

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 . Supervolcanoes occur whe ...

; other shield volcanoes—such as in the

Hawaiian Islands The Hawaiian Islands () are an archipelago of eight major volcanic islands, several atolls, and numerous smaller islets in the Pacific Ocean, North Pacific Ocean, extending some from the Hawaii (island), island of Hawaii in the south to nort ...

—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 Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

around the

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

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: lithost ...

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

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

and

Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...

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

Paleosol In Earth science, geoscience, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The definition of the term in geology and paleontology is slightly different from its use in soil science. In geo ...

) profiles and

lacustrine A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from t ...

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 (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

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 Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

and some pyroclastic 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. The caldera, which has a diameter of around 30 kilometres, contains rich volcanic soils which supports agriculture, with the primary crop in the area being

Sugarcane Sugarcane or sugar cane is a species of tall, Perennial plant, perennial grass (in the genus ''Saccharum'', tribe Andropogoneae) that is used for sugar Sugar industry, production. The plants are 2–6 m (6–20 ft) tall with stout, jointed, fib ...

. The caldera is surrounded on most sides by mountains and plateaus. The two primary ranges which form the rim of the caldera are the mountain belt formed by the Tweed Range, Lamington Plateau and Springbrook Plateau and it’s eastward extensions consisting of ridges extending in a general northeastern direction towards the Gold Coast. This mountain belt which can be seen as one range forms the western and northern parts of the caldera rim. and the Nightcap Range to the south and a series of smaller hills to the east which are connected to the Nightcap Range. Much of the caldera is covered by Gondwana Rainforests. The ranges and plateaus fan outwards on the opposite side of the inner caldera. The rivers and creeks also generally flow in the valleys between the ridges and radiate outwards in a similar way as the mountains. Lamington National Park contains over 500 waterfalls and cascades which are from creeks which navigate through the rough terrain of the Lamington Plateau. The edge of the Lamington which meets the caldera descends steeply with layers of cliffs and offers extensive views into the caldera from various lookouts along the edge of the caldera rim which can be accessed via hiking tracks. The Springbrook Plateau, which is mostly encompassed within the namesake Springbrook National Park, is situated to the east of the Lamington Plateau. This plateau is separated from the Lamington Plateau by the Numinbah Valley, which runs from the western reaches of Advancetown Lake to the Queensland/New South Wales border which also marks the edge of the caldera. Egg Rock/Indigenous Yugambeh name: Kurraragin (440m), Turtle Rock (510m) are situated on the eastern foothills of the Lamington Plateau, at the northern tip of Ships Stern (700m), an extension of the Lamington Plateau. The two rock formations listed consist of

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

and were formed from subsidiary vents. On the edge of the rim of the Springbrook Plateau, there are many viewpoints overlooking the caldera, most of which are located on peaks such as Mount Mumdjin, Springbrook Mountain and Mount Thillinmam. West of the Springbrook Plateau is Mount Tenduragan, a small pyramidal mountain west of the main Springbrook Plateau connected by a spur. An easterly ridge which connects to the main Springbrook Plateau contains the twin peaks of Mount Cougal. Extending from the East Peak of Mount Cougal is a ridge which leads to Boyds Butte, an exposed rock feature. Further along this ridge is Tallebudgera Mountain, a roughly Y shaped plateau formed from lava flows. The Both Valleys Reserve covers much of this mountain. There are two notable gaps within the ring of mountains surrounding the caldera which allow easy access in and out of the caldera. The westerly gap is located between Mount Burrell (933m) of the Nightcap Range and Lofts Pinnacle of the Tweed Range. Kyogle Road, which runs from the namesake town of Kyogle to Murwillumbah crosses the unnamed gap. Much of the mountains in the Tweed Caldera rim are covered in various types of forest, predominantly subtropical rainforest. These various volcanic origin features have a large vertical component, and the cliffs host lithophytic species. Some notable and easily observable lithophytic plants within the Tweed Volcano area include: -Doryanthes palmeri -Hoya australis -Dendrobium kingianum -Dendrobium speciosum

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