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Geology Of American Samoa
The geology of American Samoa is part of the broader geology of the Samoan island chain. Geologic history and origins Except for Rose Atoll, the islands in the chain are geologically young, having formed within the last few million years, likely in the Pliocene or Quaternary. Preliminary mapping took place in the 1940s and 1950s, with a hiatus until the 1980s. Situated near the southwest margin of the Pacific Plate, American Samoa exhibits high volcanic mountains and submerged reef banks. Throughout the island chain, islands get larger to the west, with the eroded Rose Atoll in the east. The island chain is inferred to be related to hotspot volcanism, with alkali basalt rather than a tholeiitic magma series. On Tutuila, tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock co ... and l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
American Samoa
American Samoa is an Territories of the United States, unincorporated and unorganized territory of the United States located in the Polynesia region of the Pacific Ocean, South Pacific Ocean. Centered on , it is southeast of the island country of Samoa, east of the International Date Line and the Wallis and Futuna Islands, west of the Cook Islands, north of Tonga, and some south of Tokelau. American Samoa is the southernmost territory of the United States, situated southwest of the U.S. state of Hawaii, and one of two U.S. territories south of the Equator, along with the uninhabited Jarvis Island. American Samoa consists of the eastern part of the Samoan Islands, Samoan archipelagothe inhabited volcanic islands of Tutuila, Aunuʻu, Ofu-Olosega, Ofu, Ofu-Olosega, Olosega and Taʻū and the uninhabited Rose Atollas well as Swains Island, a remote coral atoll in the List of islands of Tokelau, Tokelau volcanic island group. The total land area is , slightly larger than Washing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58See the 2014 version of the ICS geologic time scale million years ago (Ma). It is the second and most recent epoch of the Neogene Period in the Cenozoic, Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch. Prior to the 2009 revision of the geologic time scale, which placed the four most recent major glaciations entirely within the Pleistocene, the Pliocene also included the Gelasian Stage, which lasted from 2.59 to 1.81 Ma, and is now included in the Pleistocene. As with other older geologic periods, the Stratum, geological strata that define the start and end are well-identified but the exact dates of the start a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quaternary
The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the Phanerozoic eon. It follows the Neogene Period and spans from 2.58 million years ago to the present. The Quaternary Period is divided into two epochs: the Pleistocene (2.58 million years ago to 11.7 thousand years ago) and the Holocene (11.7 thousand years ago to today); a proposed third epoch, the Anthropocene, was rejected in 2024 by IUGS, the governing body of the ICS. The Quaternary is typically defined by the Quaternary glaciation, the cyclic growth and decay of continental ice sheets related to the Milankovitch cycles and the associated climate and environmental changes that they caused. Research history In 1759 Giovanni Arduino proposed that the geological strata of northern Italy could be divided into four succ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tholeiitic Magma Series
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 into a more evolved, silica rich end member. Rock types of the tholeiitic magma series include tholeiitic basalt, ferro-basalt, tholeiitic basaltic andesite, tholeiitic andesite, dacite and rhyolite. The variety of basalt in the series was originally called ''tholeiite'' but the International Union of Geological Sciences recommends that ''tholeiitic basalt'' be used in preference to that term.Le Maitre ''et al.'' 2002 Tholeiitic rock types tend to be more enriched in iron and less enriched in magnesium and aluminium than calc-alkaline rock types. They are thought to form in a less oxidized environment than calc-alkaline rocks. Tholeiitic basalt is formed at mid-ocean ridges and makes up much of the oceanic crust. Almost all the ba ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tuff
Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock containing 25% to 75% ash is described as ''tuffaceous'' (for example, ''tuffaceous sandstone''). A pyroclastic rock containing 25–75% volcanic bombs or volcanic blocks is called tuff breccia. Tuff composed of sandy volcanic material can be referred to as volcanic sandstone. Tuff is a relatively soft rock, so it has been used for construction since ancient times. Because it is common in Italy, the Romans used it often for construction. The Rapa Nui people used it to make most of the ''moai'' statues on Easter Island. Tuff can be classified as either igneous or sedimentary rock. It is usually studied in the context of igneous petrology, although it is sometimes described using sedimentological terms. Tuff is often erroneously called t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geology Of The United States
The richly textured landscape of the United States is a product of the dueling forces of plate tectonics, weathering and erosion. Over the 4.5 billion-year history of the Earth, tectonic upheavals and colliding plates have raised great mountain ranges while the forces of erosion and weathering worked to tear them down. Even after many millions of years, records of Earth's great upheavals remain imprinted as textural variations and surface patterns that define distinctive landscapes or provinces. The diversity of the landscapes of the United States can be easily seen on the shaded relief image to the right. The stark contrast between the 'rough' texture of the western US and the 'smooth' central United States, central and eastern United States, eastern regions is immediately apparent. Differences in roughness (topographic relief) result from a variety of processes acting on the underlying rock. The plate tectonic history of a region strongly influences the rock type and structure ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
