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Ōrākei Basin
Ōrākei Basin is a tidal basin and one of the extinct volcanoes in the Auckland volcanic field in the North Island of New Zealand. It has an explosion crater around wide, with a surrounding tuff ring. The present basin is slightly larger than the original maar crater. Sediments in the basin provided the first high-resolution palaeo-environmental reconstruction for northern New Zealand of the last 130,000 years. The basin supports recreational water sports activities for the local population. Geography Ōrākei Basin is between the suburbs of Remuera and Meadowbank, adjacent to the south shore of the Waitematā Harbour, close to the harbour entrance from the Hauraki Gulf. The western side of the basin has a road that connects the inland suburb of Remuera with the coastal suburbs and the northern side has been formed into a railway embankment which the basin drains into the sea through sluice gates at its north-east corner. The Ōrākei (Te Hori) Creek drains some of the Remuer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Maar
A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallow crater lake, which may also be called a maar.David S.G. Thomas and Andrew Goudie (eds.), ''The Dictionary of Physical Geography'' (Oxford: Blackwell, 2000), 301. . Maars range in size from across and from deep. Most maars fill with water to form natural lakes. Most maars have low rims composed of a mixture of loose fragments of volcanic rocks and rocks torn from the walls of the diatreme. Etymology The name ''maar'' comes from a Moselle Franconian dialect word used for the circular lakes of the Daun area of Germany. The word evolved from its first use in German in the modern geological sense in 1819 and is now used in English and in the geological sciences as the term for the explosion crater, even if water from rainfall might alway ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Māngere Mountain
Māngere Mountain, also known by the names Te Pane-o-Mataaho and Te Ara Pueru, is a volcanic cone in Māngere, Auckland. Located within Māngere Domain, it is one of the largest volcanic cones in the Auckland volcanic field, with a peak above sea level. It was the site of a major pā (Māori people, Māori fortified settlement) and many of the pā's earthworks are still visible. It has extensive panoramic views of Auckland from its location in the southeastern portion of the city's urban area. Geography The volcano features two large craters. It has a wide crater with a lava dome near its centre, a feature shared by no other volcano in Auckland. It first erupted approximately 70,000 years ago. The mountain is one of the largest and best preserved of Auckland's volcanic cones. Most of the suburb of Māngere Bridge (suburb), Māngere Bridge was formed from the lava flows that came from the mountain's eruptions. Approximately 50,000 years ago, an eruption created hot fluid pāhoe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Taupō Volcanic Zone
The Taupō Volcanic Zone (TVZ) is a volcano, volcanic area in the North Island of New Zealand. It has been active for at least the past two million years and is still highly active. Mount Ruapehu marks its south-western end and the zone runs north-eastward through the Taupō and Rotorua areas and offshore into the Bay of Plenty. It is part of a larger Central Volcanic Region that extends to the Coromandel Peninsula and has been active for four million years. The zone is contained within the Tectonics, tectonic intra-arc continental Taupō Rift and this rift volcanic zone is widening unevenly east–west, with the greatest rate of widening at the Bay of Plenty coast, the least at Mount Ruapehu and a rate of about per year at Taupō. The zone is named after Lake Taupō, the flooded caldera of the largest volcano in the zone, the Taupō Volcano and contains a large central North Island Volcanic Plateau, volcanic plateau as well as other landforms. Activity There are numerous vol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Laschamp Event
The Laschamp or Laschamps event, also termed the Adams event, was a geomagnetic excursion (a short reversal of the Earth's magnetic field). It occurred between 42,200 and 41,500 years ago, during the Last Glacial Period. It was discovered from geomagnetic anomalies found in the Laschamps and Olby lava flows near Clermont-Ferrand, France in the 1960s. The Laschamp event was the first known geomagnetic excursion and remains the most thoroughly studied among the known geomagnetic excursions. It is named after the village of Laschamps, part of the commune of Saint-Genès-Champanelle in France. Background and effects Since its discovery, the magnetic excursion has been demonstrated in geological archives from many parts of the world. The transition from the normal field to the reversed field lasted approximately 250 years, while the magnetic field remained reversed for approximately 440 years. During the transition, Earth's magnetic field declined to a minimum of 5% of it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Luminescence Dating
Luminescence dating refers to a group of chronological dating methods of determining how long ago mineral grains were last exposed to sunlight or sufficient heating. It is useful to geologists and archaeologists who want to know when such an event occurred. It uses various methods to stimulate and measure luminescence. It includes techniques such as optically stimulated luminescence (OSL), infrared stimulated luminescence (IRSL), radiofluorescence (RF), infrared photoluminescence (IR-PL) and thermoluminescence dating (TL). "Optical dating" typically refers to OSL and IRSL, but not TL. The age range of luminescence dating methods extends from a few years to over one million years for red TL. Since the early applications of luminescence dating in the 1960/1970s, the field has received growing attention in the scientific community, with more than 3500 publications per year and >200 laboratories across the globe in 2020. Conditions and accuracy All sediments and soils contain trace ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Argon–argon Dating
Argon–argon (or 40Ar/39Ar) dating is a radiometric dating method invented to supersede Potassium-argon dating, potassiumargon (K/Ar) dating in accuracy. The older method required splitting samples into two for separate potassium and argon measurements, while the newer method requires only one rock fragment or mineral grain and uses a single measurement of isotopes of argon, argon isotopes. 40Ar/39Ar dating relies on neutron irradiation from a nuclear reactor to convert a stable form of potassium (39K) into the radioactive 39Ar. As long as a standard of known age is co-irradiated with unknown samples, it is possible to use a single measurement of argon isotopes to calculate the 40K/40Ar* ratio, and thus to calculate the age of the unknown sample. 40Ar* refers to the radiogenic 40Ar, i.e. the 40Ar produced from radioactive decay of 40K. 40Ar* does not include atmospheric argon adsorbed to the surface or inherited through diffusion and its calculated value is derived from measuring t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tephrochronology
250px, Tephra horizons in south-central Iceland. The thick and light coloured layer at the height of the volcanologist's hands is rhyolitic tephra from Hekla. Tephrochronology is a Geochronology, geochronological technique for dating archaeological, geological and palaeoenvironmental sequences and events by their location between upper and lower layers of tephra (volcanic ejecta) of known date, and for correlating such sequences and events at separate locations between the same layers. The premise of the technique is that each volcanic event produces a "tephra horizon", a layer of ash with a unique chemical "fingerprint" that allows the deposit to be identified across the area affected by fallout. Thus, once the volcanic event has been independently dated, the tephra horizon will act as time marker. It is a variant of the basic geological technique of stratigraphy. The main advantages of the technique are that the volcanic ash layers can be relatively easily identified in many ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radiocarbon Age
Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon. The method was developed in the late 1940s at the University of Chicago by Willard Libby. It is based on the fact that radiocarbon () is constantly being created in the Earth's atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting combines with atmospheric oxygen to form radioactive carbon dioxide, which is incorporated into plants by photosynthesis; animals then acquire by eating the plants. When the animal or plant dies, it stops exchanging carbon with its environment, and thereafter the amount of it contains begins to decrease as the undergoes radioactive decay. Measuring the amount of in a sample from a dead plant or animal, such as a piece of wood or a fragment of bone, provides information that can be used to calc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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: lithostratigraphy (lithologic stratigraphy), biostratigraphy (biologic stratigraphy), and chronostratigraphy (stratigraphy by age). Historical development Catholic priest Nicholas Steno established the theoretical basis for stratigraphy when he introduced the law of superposition, the principle of original horizontality and the principle of lateral continuity in a 1669 work on the fossilization of organic remains in layers of sediment. The first practical large-scale application of stratigraphy was by William Smith in the 1790s and early 19th century. Known as the "Father of English geology", Smith recognized the significance of strata or rock layering and the importance of fossil markers for correlating strata; he created the first geo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Before Present
Before Present (BP) or "years before present (YBP)" is a time scale used mainly in archaeology, geology, and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Because the "present" time changes, standard practice is to use 1January 1950 as the commencement date (epoch) of the age scale, with 1950 being labelled as the "standard year". The abbreviation "BP" has been interpreted retrospectively as "Before Physics", which refers to the time before nuclear weapons testing artificially altered the proportion of the carbon isotopes in the atmosphere, which scientists must account for when using radiocarbon dating for dates of origin that may fall after this year. In a convention that is not always observed, many sources restrict the use of BP dates to those produced with radiocarbon dating; the alternative notation "RCYBP" stands for the explicit "radio carbon years before present". Usage The BP scale is s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oruanui Eruption
The Oruanui eruption (also known as the Kawakawa eruption or Kawakawa/Oruanui event) of Taupō Volcano in New Zealand around 25,700 years before present was the world's most recent supereruption, and its largest phreatomagmatic eruption characterised to date. Geography At the time of the eruption, the sea level was much lower than at present, and for over 100,000 years the Taupō Volcano had been mainly under Lake Huka, a larger lake than the present Lake Taupō. Lake Huka was destroyed in the eruption, and other features of the local geography were changed significantly as outlined below. Eruption With a Volcanic Explosivity Index of 8, it is one of the largest eruptions ever to occur in New Zealand and the most recent supereruption. It occurred years BP in the Late Pleistocene. It generated approximately of pyroclastic fall deposits, of pyroclastic density current (PDC) deposits (mostly ignimbrite), and of primary intracaldera material, equivalent to of rhyolitic m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
