Woodcock, Robin A. Strachan Geological history of Britain and Ireland. In Robert D. Hatcher Jr. Geological Society of America. Park The environment: principles and applications 2nd ed. CliffsQuickReview Earth Science. Reference cited. Science : —6. Bibcode: Sci… PMID Oceanic hotspots: intraplate submarine magmatism and tectonism. Isostasy and flexure of the lithosphere. Cambridge University Press. Continental tectonics. Geological society. Environment COP26 nears conclusion with mixed signals and frustration.
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Mounting pressure within the reservoir may drive the magma further upward through structurally weak zones to erupt as lava at the surface. In a continental environment, magmas are generated in the Earth's crust as well as at varying depths in the upper mantle. The variety of molten rocks in the crust, plus the possibility of mixing with molten materials from the underlying mantle, leads to the production of magmas with widely different chemical compositions. An idealized diagram of a volcano in an oceanic environment left and in a continental environment right.
I f magmas cool rapidly, as might be expected near or on the Earth's surface, they solidify to form igneous rocks that are finely crystalline or glassy with few crystals. Accordingly, lavas, which of course are very rapidly cooled, form volcanic rocks typically characterized by a small percentage of crystals or fragments set in a matrix of glass quenched or super-cooled magma or finer grained crystalline materials.
If magmas never breach the surface to erupt and remain deep underground, they cool much more slowly and thus allow ample time to sustain crystal precipitation and growth, resulting in the formation of coarser grained, nearly completely crystalline, igneous rocks. Subsequent to final crystallization and solidification, such rocks can be exhumed by erosion many thousands or millions of years later and be exposed as large bodies of so-called granitic rocks, as, for example, those spectacularly displayed in Yosemite National Park and other parts of the majestic Sierra Nevada mountains of California.
Two Polynesian terms are used to identify the surface character of Hawaiian lava flows. This chain formed as a result of the collision between the Indian subcontinent and Asia some 25 million years ago, and has given rise to the tallest mountain in the world — Mt. Block mountains are caused by faults in the crust, a seam where rocks can move past each other. Also known as rifting, this process occurs when rocks on one side of a fault rise relative to the other.
The uplifted blocks become block mountains also known as horsts while the intervening dropped blocks are known as graben i. There is also the East African Rift, an active continental rift zone with several active volcanoes that extends from Eritrea to Mozambique. As noted, the final way in which mountains are formed is through erosion. This occurs during and after an uplift, where a newly formed mountainous region is subjected to the effects of wind, water, ice, and gravity.
These forces actively shape the surface of mountain ranges, wearing down the exposed surfaces, depositing sediment in alluvial flows, and leading to the formation of characteristic landforms. Plateau mountains, such as the Catskills, are formed from the erosion of an uplifted plateau. And after millions of years of erosion, mountains may cease to exist entirely.
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