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Pilot Knob (Austin, Texas)
Pilot Knob is the eroded core of an extinct volcano located south of central Austin, Texas, near Austin-Bergstrom International Airport and McKinney Falls State Park. Introduction Pilot Knob is one of around 75 late-Cretaceous Period volcanic complexes scattered around Central Texas from Waco to Austin, San Antonio, and Del Rio. All of these volcanoes have been extinct for millions of years. The Pilot Knob volcanic complex consists of four small, rounded hills (including Pilot Knob proper) forming the volcano's core area in an area two miles in diameter. The hills are composed of trap rock which is an erosion-resistant, fine-grained mafic volcanic rock. The complex rises above a circular lowland drained by Cottonmouth Creek and is underlain chiefly by volcanic ash and other pyroclastic debris. Several smaller bodies of trap rock occur in the volcanic ash. A topographic rim surrounding the Cottonmouth Creek lowland to the north is formed by sedimentary rock, mainly lithified ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Austin, Texas
Austin is the capital city of the U.S. state of Texas, as well as the county seat, seat and largest city of Travis County, Texas, Travis County, with portions extending into Hays County, Texas, Hays and Williamson County, Texas, Williamson counties. Incorporated on December 27, 1839, it is the List of United States cities by population, 11th-most-populous city in the United States, the List of cities in Texas by population, fourth-most-populous city in Texas, the List of capitals in the United States, second-most-populous state capital city, and the most populous state capital that is not also the most populous city in its state. It has been one of the fastest growing large cities in the United States since 2010. Downtown Austin and Downtown San Antonio are approximately apart, and both fall along the Interstate 35 corridor. Some observers believe that the two regions may some day form a new "metroplex" similar to Dallas–Fort Worth metroplex, Dallas and Fort Worth. Austin i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of the entire Phanerozoic. The name is derived from the Latin ''creta'', "chalk", which is abundant in the latter half of the period. It is usually abbreviated K, for its German translation ''Kreide''. The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now- extinct marine reptiles, ammonites, and rudists, while dinosaurs continued to dominate on land. The world was ice free, and forests extended to the poles. During this time, new groups of mammals and birds appeared. During the Early Cretaceous, flowering plants appeared and began to rapidly diversify, becoming the dominant group of plants across the Earth b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tertiary
Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start of the Cenozoic Era, and extended to the beginning of the Quaternary glaciation at the end of the Pliocene Epoch. The time span covered by the Tertiary has no exact equivalent in the current geologic time system, but it is essentially the merged Paleogene and Neogene periods, which are informally called the Early Tertiary and the Late Tertiary, respectively. The Tertiary established the Antarctic as an icy island continent. Historical use of the term The term Tertiary was first used by Giovanni Arduino during the mid-18th century. He classified geologic time into primitive (or primary), secondary, and tertiary periods based on observations of geology in Northern Italy. Later a fourth period, the Quaternary, was applied. In the early d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Taylor Group
The Taylor Group is a geologic group in Arkansas. It preserves fossils dating back to the Cretaceous period. See also * List of fossiliferous stratigraphic units in Arkansas * Paleontology in Arkansas Paleontology in Arkansas refers to paleontological research occurring within or conducted by people from the United States, U.S. state of Arkansas. The fossil Fossil record, record of Arkansas spans from the Ordovician to the Eocene. Nearly all of ... References * Geologic groups of Arkansas Cretaceous System of North America {{Cretaceous-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Onion Creek (Texas)
Onion Creek is a small tributary stream of the Colorado River in Texas. It begins southeast of Johnson City, Blanco County, Texas, and flows approximately eastward into the Colorado River, northwest of Garfield in Travis County, Texas. While areas surrounding the creek's origin in Blanco County are primarily rural, areas closer to its mouth in Travis County have more urban and industrial development. Passing near Dripping Springs, Driftwood, and Onion Creek, Onion Creek is the source of the waterfalls in McKinney Falls State Park. Onion Creek's watershed spans an area of . 2013 Flood On October 31, 2013 Onion Creek experienced historic levels of flooding, cresting at 40.15 ft, a level not seen since 1921. Over the course of 4h 9-10in of rain fell in the Onion Creek watershed. The flood had a flow rate of over 120,000 cubic feet per second, more than twice that of Niagara Falls. In the end, five people died and more than 500 homes were damaged by flood waters. As a res ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cone Sheet
A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines connecting a common point, the apex, to all of the points on a base that is in a plane that does not contain the apex. Depending on the author, the base may be restricted to be a circle, any one-dimensional quadratic form in the plane, any closed one-dimensional figure, or any of the above plus all the enclosed points. If the enclosed points are included in the base, the cone is a solid object; otherwise it is a two-dimensional object in three-dimensional space. In the case of a solid object, the boundary formed by these lines or partial lines is called the ''lateral surface''; if the lateral surface is unbounded, it is a conical surface. In the case of line segments, the cone does not extend beyond the base, while in the case of half-lin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or underwater, usually at temperatures from . The volcanic rock resulting from subsequent cooling is also often called ''lava''. A lava flow is an outpouring of lava during an effusive eruption. (An explosive eruption, by contrast, produces a mixture of volcanic ash and other fragments called tephra, not lava flows.) The viscosity of most lava is about that of ketchup, roughly 10,000 to 100,000 times that of water. Even so, lava can flow great distances before cooling causes it to solidify, because lava exposed to air quickly develops a solid crust that insulates the remaining liquid lava, helping to keep it hot and inviscid enough to continue flowing. The word ''lava'' comes from Italian and is probably derived from the Latin word ''labes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Subaerial Eruption
A subaerial eruption is any sort of volcanic eruption that occurs on the Earth's surface, or in the open air subaerial, 'under the air', and not underwater or underground. They generally produce pyroclastic flows, lava fountains, and lava flows, which are commonly classified in different subaerial eruption types, including Plinian eruption, Plinian, Peléan eruption, Peléan, and Hawaiian eruptions. Subaerial eruptions contrast with Wiktionary:subaqueous, subaqueous, submarine eruption, submarine and subglacial eruptions which all originate below differing forms of a water surface. References Volcanic eruption types {{Types of volcanic eruptions ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Marl
Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. Marl makes up the lower part of the cliffs of Dover, and the Channel Tunnel follows these marl layers between France and the United Kingdom. Marl is also a common sediment in post-glacial lakes, such as the marl ponds of the northeastern United States. Marl has been used as a soil conditioner and neutralizing agent for acid soil and in the manufacture of cement. Description Marl or marlstone is a carbonate-rich mud or mudstone which contains variable amounts of clays and silt. The term was originally loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay and calcium carbonate, formed under freshwater conditions. These typically contain 35–65% clay and 65–35% carbonate. The te ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life. About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone. The remaining carbonate rock is mostly dolomite, a closely related rock, which contains a high percentage of the mineral dolomite, . ''Magnesian limestone'' is an obsolete and poorly-defined term used variously for dolomite, for limes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Volcanic Cone
Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and size of the fragments ejected during the eruption. Types of volcanic cones include stratocones, spatter cones, tuff cones, and cinder cones. Stratocone 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. Some have collapsed craters called calderas. The central core of a stratocone is commonly dominated by a central core of intrusive rocks that range from around to over several kilometers in diameter. This central core is surrounded by multiple generations of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Volcanic Ash
Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcano, volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer to all explosive eruption products (correctly referred to as ''tephra''), including particles larger than 2 mm. Volcanic ash is formed during explosive volcanic eruptions when dissolved gases in magma expand and escape violently into the atmosphere. The force of the gases shatters the magma and propels it into the atmosphere where it solidifies into fragments of volcanic rock and glass. Ash is also produced when magma comes into contact with water during phreatomagmatic eruptions, causing the water to explosively flash to steam leading to shattering of magma. Once in the air, ash is transported by wind up to thousands of kilometres away. Due to its wide dispersal, ash can have a number of impacts on society, including animal a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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