The Seven Sisters are a series of seven volcanic cinder cones on the Atherton Tableland, near Yungaburra, Queensland, Australia. They were formed over 350,000 years ago. [1]
A cinder cone is a steep conical hill of loose pyroclastic fragments, such as either volcanic clinkers, volcanic ash, or cinder that has been built around a volcanic vent. The pyroclastic fragments are formed by explosive eruptions or lava fountains from a single, typically cylindrical, vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as either cinders, clinkers, or scoria around the vent to form a cone that often is symmetrical; with slopes between 30–40°; and a nearly circular ground plan. Most cinder cones have a bowl-shaped crater at the summit.
The Atherton Tableland is a fertile plateau which is part of the Great Dividing Range in Queensland, Australia. The Atherton Tablelands is a diverse region, covering an area of 64,768 square kilometres and home to 45,243 people. The main population centres on the Atherton Tablelands are Mareeba and Atherton. Smaller towns include Tolga, Malanda, Herberton, Kuranda, Ravenshoe, Millaa Millaa, Chillagoe, Dimbulah, Mt Garnet, Mt Molloy, Tinaroo and Yungaburra.
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. It is the largest country in Oceania and the world's sixth-largest country by total area. The neighbouring countries are Papua New Guinea, Indonesia, and East Timor to the north; the Solomon Islands and Vanuatu to the north-east; and New Zealand to the south-east. The population of 25 million is highly urbanised and heavily concentrated on the eastern seaboard. Australia's capital is Canberra, and its largest city is Sydney. The country's other major metropolitan areas are Melbourne, Brisbane, Perth, and Adelaide.
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The vents have an overall southwest-northeast alignment, which suggests that the ascending magma utilised a pre-existing fracture within the earth's crust. [2] Several of the craters are breached to the southeast, possibly due to the prevailing southeast winds blowing ash and scoria to the northwest and so building the cones more to that side. Parts of the rocky basalt flows are still densely forested and can be seen surrounding the Curtain Fig Tree.
Scoria is a highly vesicular, dark colored volcanic rock that may or may not contain crystals (phenocrysts). It is typically dark in color, and basaltic or andesitic in composition. Scoria is relatively low in density as a result of its numerous macroscopic ellipsoidal vesicles, but in contrast to pumice, all scoria has a specific gravity greater than 1, and sinks in water. The holes or vesicles form when gases that were dissolved in the magma come out of solution as it erupts, creating bubbles in the molten rock, some of which are frozen in place as the rock cools and solidifies. Scoria may form as part of a lava flow, typically near its surface, or as fragmental ejecta, for instance in Strombolian eruptions that form steep-sided scoria cones. Most scoria is composed of glassy fragments, and may contain phenocrysts. The word scoria comes from the Greek σκωρία, skōria, rust. A colloquial term for scoria is cinder.
Basalt is a mafic extrusive igneous rock formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. More than 90% of all volcanic rock on Earth is basalt. Basalt lava has a low viscosity, due to its low silica content, resulting in rapid lava flows that can spread over great areas before cooling and solidification. Flood basalt describes the formation in a series of lava basalt flows.
Curtain Fig Tree is a heritage-listed tree at Curtain Fig Tree Road, Yungaburra, Tablelands Region, Queensland, Australia. It is one of the largest trees in Tropical North Queensland, Australia, and one of the best known attractions on the Atherton Tableland. It was added to the Queensland Heritage Register on 3 December 2009.
