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A branch of physics that studies atoms as isolated systems of electrons and an atomic nucleus. Compare nuclear physics. atomic structure atomic weight (A) The sum total of protons (or electrons) and neutrons within an atom. audio frequency A periodic vibration whose frequency is in the band audible to the average human, the human hearing range.
Augustine Volcano (Alaska) during its eruptive phase on January 24, 2006. A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
Volcanoes, he said, were formed where the rays of the sun pierced the earth. The volcanoes of southern Italy attracted naturalists ever since the Renaissance led to the rediscovery of Classical descriptions of them by wtiters like Lucretius and Strabo. Vesuvius, Stromboli and Vulcano provided an opportunity to study the nature of volcanic ...
Volcanoes are usually mountains (sometimes islands, lakes, plateaus, calderas, seamounts or lava domes) that are formed when magma (liquid rock) wells up from inside the Earth. There are also analogous formations away from the Earth. Many volcanoes are categorized both as volcanoes and other landforms, such as mountains (if qualified).
On Earth, volcanoes are most often found where tectonic plates are diverging or converging, and because most of Earth's plate boundaries are underwater, most volcanoes are found underwater. For example, a mid-ocean ridge , such as the Mid-Atlantic Ridge , has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has ...
In 1980, volcanologist George P. L. Walker proposed the Hatepe eruption as the representative of a new class called ultra-Plinian deposits, based on its exceptional dispersive power and eruptive column height. [8] A dispersal index of 50,000 square kilometres (19,000 sq mi) has been proposed as a cutoff for an ultra-Plinian eruption. [8]
A fumarole (or fumerole) [1] is a vent in the surface of the Earth or another rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcanic activity , but fumarole activity can also precede a volcanic eruption and has been used for ...
A volcanic arc (also known as a magmatic arc [1]: 6.2 ) is a belt of volcanoes formed above a subducting oceanic tectonic plate, [2] with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench , with the arc located further from the subducting plate than the trench.