The Notions of Hot Springs, Stalactites and Lahars - Assignment Example

Geologic Terms. Hot Springs. Hot springs are generally associated with volcanic areas and are springs with water whose temperature is substantially higher than the air temperature of the surrounding region. There are three requirements for the formation of Hot Springs: an abundant supply of surface water, a volcanic heat source and a plumbing system. Precipitated rain water percolates down through porous sand and gravel, and cracks and fissures in the earth, to a depth of about 7,000 feet. Here it comes into contact with molten rock, or magma, either active or recently solidified, but still at a high temperature. The water is heated up to 500o F but does not vaporize, because of the pressure it is subjected to. A plumbing system, made up of channels of fissures and cracks, often along fault lines, pushes the heated water to the surface as a Hot Spring. Hot Springs which eject plumes of water and vapor are called geysers. Fumaroles are Hot Springs which appear as steam vents, emitting a mixture of steam and gases. (UnMuseum website). Stalactites. Stalactites, along with stalagmites, are dripstone mineral features found in caves and are called speleothems (derived from the Greek ‘spelaion’ for cave and ‘them’ for deposit). A stalactite is an icicle-shaped mass of calcite which is attached to the roof of a limestone cavern. Groundwater, which contains dissolved calcium bicarbonate, percolates through cracks in the roof of limestone caves. When a drop of water comes into contact with the air in the cave, some calcium dioxide is lost and a part of the calcium bicarbonate is changed into calcium carbonate, or calcite. Calcite is precipitated out of the water solution and forms a ring-like deposit on the cave roof. Successive drops increase the length and thickness of the ring and water drips through the hollow center, forming a pendant cylinder. Stalactites join with stalagmites to form pillars and curtains. Since air is a prerequisite for stalactite formation, the presence of stalactites indicates that the cave was above the water table during dripstone formation. (The Columbia Encyclopedia. The U.S. Geological Survey website). Lahars. Lahar is an Indonesian word for a volcanic mudflow, or debris flow, which is a rapidly flowing mixture of rock debris and water which originates on the slopes of a volcano. Lahars vary in size and speed and resemble a mass of wet concrete which carries rock debris ranging from clay to large boulders. Lahars can be triggered by (1) volcanic eruptions which eject water from a crater lake or rapidly melt snow and ice (2) heavy rainfall which erodes loose volcanic rock and soil on hillsides and river valleys (3) sudden breakout of lakes dammed by volcanic deposits (4) sudden landslides or debris avalanches. Lahars have dangerous consequences. The direct impact of the lahar can crush or destroy everything in it’s’ path. Villages and communities are buried in the debris, bridges and roads are destroyed, leaving people trapped. The increased deposition of sediment can bury towns and agricultural lands and block tributary stream valleys, causing flooding of upstream areas and sudden floods. (U.S. Geological Survey website). Erosion. Erosion is the process by which the rock and soil of the earth’s crust are loosened, dissolved, or worn away and simultaneously moved from one place to another. The agents of erosion are water, wind, ice and gravity. Moving water is the primary agent of erosion. Pounding waves along the coast continuously alter the shoreline, wearing away cliffs and beaches over time and carry pebbles and other sediments which cause weathering. Running water in creeks, streams and rivers erodes the riverbed by cutting into the bedrock. Falling rain loosens and carries away the topsoil. Glaciers are moving sheets of ice which carry rock, soil and vegetation along with them, wear away the bedrock and gouge valleys from mountain slopes. The wind is a forceful agent of erosion in areas which lack ground cover, particularly when it carries particles of sand. Gravity brings about erosion indirectly by its downward pulling effect on running water and also directly, by causing rock falls and avalanches. Burrowing and hoofed animals, plant roots and men are also agents of erosion. An important part of erosion is weathering, which is the chemical and physical breakdown of rocks at or near the earth’s surface. Weathering can be mechanical, involving the physical disintegration of rocks, due to gravity, heat, friction and moisture. It can also be chemical, involving the decomposition of rock due to dissolution, oxidation and hydrolysis. (Science of Everyday Things website). Earthquakes. Earthquakes are vibrations of the earth caused by the sudden release of energy along faults, due to the displacement of rocks. According to the Elastic Rebound Hypothesis, strain builds up in rocks until it exceeds the elastic limit of the rocks. This causes the rock to rupture at a point, releasing energy in the form of radiating seismic waves. The study of earthquakes is called seismology and seismographs are instruments which detect, record and measure seismic waves. Earthquakes have a focus, which is the source of the energy release and an epicenter, which is the point on the earth’s surface directly above the focus. Based on the depth of the foci, earthquakes can be categorized as shallow focus (less than 70 km depth), intermediate focus (70-300 km depth) and deep focus (greater than 300 km). Shallow focus earthquakes cause the greatest destruction. Ground damage is often aggravated by fires, tsunamis and landslides. Earthquakes are difficult to predict accurately. (Green). Pangaea. The Theory of Continental Drift was first proposed by the German meteorologist, Alfred Wegener, in 1912. According to this theory, the present-day continents were but fragmented pieces of large landmasses, or supercontinents, which existed millions of years ago. During the late Paleozoic Age (250 million years ago), through a series of continental collisions, all the continental landmasses assembled into a single mega continent, called Pangaea, meaning ‘all lands’ in Greek, which was surrounded by a Pangaea can be considered a ‘patchwork’ supercontinent. Pangaea held together for about 100 million years. Then, in the late Triassic Age (about 220 million years ago) Pangaea gradually broke into two mega continental landmasses: Laurasia in the Northern hemisphere, consisting of present-day North America, Greenland, Europe and Asia; Gondwana in the Southern hemisphere consisting of present-day South America, Africa, India, Australia and Antarctica. Wegener supported his theory by noting the matching coastlines of Africa and North America and the presence of identical fossil species in both coasts. He also proposed that other mismatches of geology and climate suggested that continents had drifted from earlier positions nearer to the equator. (U.S. Geological Survey website). Paleozoic Era. According to the geologic time scale, using relative dating and radioactive dating, geologic time is approximated at about 4.55 billion years. This is divided into two great time periods: (1) the Precambrian Age, dating from the formation of the earth 4500 million years ago until about 570 million years ago (2) the Phanerozoic Era, dating from 570 million years ago continuing up to the present. The Phanerozoic Eon is subdivided into three eras: the Paleozoic, the Mesozoic and the Cenozoic. The Paleozoic Era (570-200 million years ago) is further divided into the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian and Triassic eras. Sea level rise, with continental flooding, followed by sea level fall, with continental erosion, was characteristic of the Paleozoic era. Plate collisions along subduction zones bunched up continental land masses and a vast ocean covered the rest of the planet. Mountains were built by colliding plates. The supercontinent Pangaea was formed, surrounded by the single ocean, the Panthalassa and a smaller eastern sea, the Tethys. Mountain ranges replaced forests, swamps and coral reefs. Shallow seas became isolated and dried up. Entire ecosystems became extinct. In the Early Paleozoic era there was an explosion in the diversity of animal life. Later, animals, plants and fungi colonized the land and insects took to the air. In the Late Paleozoic era, there was a mass extinction. (U.S. Geological Survey website). Precambrian Era. The Precambrian Era can be divided into the Hadean (4.5-4 million years ago), Archaean (4-2.5 million years ago) and Proterozoic (2.6-.6 million years ago) eras. The Hadean eon encompassed the formation of the solar system. Particles of dust and gas surrounding the sun coalesced into planetesimals, which aggregated to form planets. The earth gradually cooled from molten to solid rock. In the Archaean period, the earth’s crust cooled and continental plates formed. The atmosphere consisted of methane, ammonia and other reducing, toxic gases. The first life forms emerged, consisting of stromatolites, or photosynthetic bacteria. In the Proterozoic period, stable continents formed and living organisms, such as bacteria, archaeans and eukaryotic cells appeared. Oxygen began to build up in the atmosphere. (Collins. University of California, Museum of Paleontology website). Terrane. Terranes are lithospheric fragments, or pieces of tectonic plates, either continental or oceanic in origin, which are sufficiently large and share similar geologic characteristics. Terranes have individual geologic histories which differ from that of the surrounding area and are bounded by faults. Accreted terranes are pieces of plate which have broken off and drifted large distances before attaching themselves to other terranes or continental land masses. Terranes that are out of place geologically are called exotic or suspect terranes. The study of terranes is called terrane tectonics or terrane analysis. Terranes are recognized by the foreign origin of its’ rock strata. (U.S. Geological Society website). Basin and Dome. A basin is a broad tract of land in which the rock strata are tilted towards a common center. They are geological depressions in which thick layer of sediment has accumulated. Basins are bowl shaped or elongated. They are formed through tectonic processes in areas where the earth’s crust has warped downwards. Basins have concentric layers with the strata growing progressively younger, with the youngest strata in the center. A dome is the inverse of a basin. Domes are circular or oval. Domes slope outward in all directions from the highest point. The rock strata is warped upwards. The concentric layers in the dome grow progressively older, with the oldest strata in the center. (The Free Dictionary online). Works Cited. Green, Nathan. Earthquakes. Introduction to Geology. Accessed on 11 March 2008 from < http://www.geo.ua.edu/intro03/quakes.html > Structural Basin. The Free Dictionary. Accessed on 11 March 2008 from < http://encyclopedia.thefreedictionary.com/Basin+(geology) > Science of Everyday Things website. Erosion. The Gale Group, Inc, 2002. Accessed on 11 March 2008 from < http://www.answers.com/topic/erosion > Collins, Allen. Web Geological Time Machine. Accessed on 11 March 2008 from < http://www.ucmp.berkeley.edu/help/timeform.html > The Columbia Encyclopedia, Sixth Edition. 2007. Stalactites and Stalagmites. Accessed On11March 11, 2008 from < http://www.encyclopedia.com/doc/1E1-stalacti.html > U.S. Geological Survey. Geology of Caves. Modified from W.E. Davies and I.M. Morgan. Accessed on 11 March 2008 from < http://geomaps.wr.usgs.gov/parks/cave/index.html > U.S. Geological Survey. Volcano Hazards Program. Lahars and their Effects – Pathways of Destruction. Accessed on 11 March 2008 from < http://volcanoes.usgs.gov/Hazards/What/Lahars/lahars.html > U.S. Geological Survey. Historical Perspectives. Accessed on 11 March 2008 from < http://pubs.usgs.gov/gip/dynamic/historical.html > U.S. Geological Survey. What is Geologic Time? Accessed on 11 March 2008 from < http://geomaps.wr.usgs.gov/parks/gtime/gtime2.html > U.S. Geological Survey. What went on before the break-up of Pangaea? Accessed on 11 March 2008 from < http://pubs.usgs.gov/gip/dynamic/Pangaea.html > UnMuseum website. Weird Geology and Geysers. Accessed on 11 March 2008 from < http://www.unmuseum.org/geysers.htm > Read More