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Scoria or cinder is a pyroclastic, highly vesicular, dark-colored volcanic rock formed by ejection from a volcano as a molten blob and cooled in the air to form discrete grains called clasts. [ 1 ] [ 2 ] It is typically dark in color (brown, black or purplish-red), and basaltic or andesitic in composition.
A cinder cone (or scoria cone [1]) is a steep conical hill of loose pyroclastic fragments, such as volcanic clinkers, volcanic ash, or scoria that has been built around a volcanic vent. [ 2 ] [ 3 ] The pyroclastic fragments are formed by explosive eruptions or lava fountains from a single, typically cylindrical, vent.
The volcano is named for William Taylor, who purchased the land in 1845. [3] The volcano's lower slopes and scoria mounds to the east and south were quarried away following European settlement, with only the north-west section of the volcanic area remaining. [3] The area around the volcanic cone became a public reserve in the 1920s. [3]
Lava lakes often form in the centre of scoria cones; if the lava in such a lake breaches the side of the cone, the result is a breached scoria cone, such as Mount Elephant. [1] The volcano first erupted approximately 184,000 years ago, within a tolerance of 38,000 years, according to argon-argon dating research first published 21 February 2017. [2]
Stratocones are large cone-shaped volcanoes made up of lava flows, explosively erupted pyroclastic rocks, and igneous intrusives that are typically centered around a cylindrical vent. Unlike shield volcanoes , they are characterized by a steep profile and periodic, often alternating, explosive eruptions and effusive eruptions .
It is the youngest onshore volcano of the Auckland volcanic field, having been formed by an eruption around 10,000 years ago. [2] It is the largest of Auckland's scoria cones and has a near-circular base with a flattish rim and three small craters. [3] [4] It is situated in the Mount Wellington suburb of Central Auckland.
[2] [4] These faults and regional fractures have given way to radial faults resulting in scoria cones and lava domes throughout the serra. [2] [4] The volcano of Sete Cidades is distinguished by two stratigraphic layers: The inferior group includes the oldest deposits associated with subaerial eruptions occurring more than 200,000 years B.C.
Mount Leura, together with nearby Mount Sugarloaf, forms part of a large extinct volcanic complex known as the "Leura Maar". [2] [3] The complex includes a broad shallow maar crater measuring 2.5 km by 1.7 km surrounded by a low tuff ring, inside which are the secondary eruption points of Mount Leura and several smaller unnamed mounds and cones of scoria.