Lava Flows middot Basalt middot An desire middot Rhyolite -3 different lava comp
ID: 236313 • Letter: L
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Lava Flows middot Basalt middot An desire middot Rhyolite -3 different lava compositions lead to very different types of lava flows (know relative flow dimensions (lengths & thicknesses) and distance the flows travel) -Associated volcanoes? (what volcanoes produce which types of lava?) -Hazards? Know the effects of lava flows on people and property -Example: Kilauea -Tephra Fall (ash, lapilli, bombs) -Associated volcanoes? -Hazards? What is the deadliest hazard associated with tephra fall? Proximal Hazards? (close to the eruption,Explanation / Answer
Volcanic explosions cause aggressive changes on earth. These powerful explosive eruptions radically change land and water around a volcano, and the minute liquid droplets of sulfuric acid exploded into the stratosphere can change earth’s climate temporarily. Eruptions often force people living near volcanoes to abandon their land and homes, sometimes forever.
There are numerous kinds of events due to volcanic action and it can be dangerous to life and property. These include lava flows, lahars, ash falls, debris avalanches, and pyroclastic density currents
Lava flows
Lava flows are flows of molten rock that pour or ooze through an erupting vent. It occurred during either non explosive activity or explosive eruptions. The speed of lava flows across the ground depends on several factors such as (1) form of lava erupted and its viscosity; (2) gradient of the ground through which it travels; (3) whether the lava flows as a wide sheet, through a confined channel, or down a lava tube; and (4) rate of lava creation at the vent.
Fluid basalt flows can move tens of kilometers from an erupting vent. These basalt flows can travel at a rate of 10 km/h (6 mph) on sharp slopes but they usually advance less than 1 km/h (0.27 m/s or about 1 ft/s) on mild slopes.
Viscous andesite flows move only a few kilometers per hour and seldom extend more than 8 km from their vents. Viscous dacite and rhyolite flows regularly form steep-sided mounds called lava domes from an erupting vent. Lava domes frequently grow by the extrusion of many individual flows >30 m thick over a period of some months or years. Such flows will overlie one another and normally move less than a few meters per hour.
Everything in the path of an advancing lava flow will be tapped over, enclosed, covered, or ignited by the enormously hot temperature of lava. When lava erupts under a glacier or flows over snow and ice, melt water from the ice and snow can cause far-reaching lahars. If it goes into a body of water or water enters a lava tube, the water may boil aggressively and cause an explosive shower of molten splash over a wide area. Methane gas, produced as lava buries vegetation, can drift in subsurface voids and burst when heated. Thick viscous lava flows, mainly those that build a dome, can fall down to form fast-moving pyroclastic flows.
Deaths caused directly by lava flows are unusual because most flows slowly and people can move out their easily. Deaths by lava flows are mainly due to related causes, such as explosions when lava interacts with water, the collapse of an active lava delta that forms where lava enters a body of water, pyroclastic flows from a collapsing dome, and lahars from melt water.
Tephra/Ash
All volatile volcanic eruptions produce tephra, fragments of rocks are formed when magma or rock is explosively expelled. The largest fragments, blocks and can be ejected with huge force but are deposited near the eruptive vent. Lapilli-sized material can be carried upward within in a volcanic plume and downwind in a volcanic cloud, but fall to the ground as the eruption cloud cools. The smallest material, volcanic ash is easily convected upward within the plume and carried downwind for very long distances; as it falls out of suspension it can potentially affect communities and farmland across hundreds, or even thousands, of square kilometers.
Ash fall not often endangers human lives, but it can have disturbing effects on the things. Due to its fine-grained rough character and extensive distribution by wind, ashfall and volcanic ash clouds are a chief risk to aviation. Ash fallout to the ground can create important distraction and damage to buildings, transportation, water, power supply, communications equipment, agriculture, and primary production leading to potentially substantial societal impacts and costs. Additionally, it can cause health impacts to humans and animals.
Pyroclastic flows
Pyroclastic flows consist of high-density mix of hot lava blocks, pumice, ash and volcanic gas. They travel at very high speed down volcanic slopes, normally following valleys. Most pyroclastic flows consist of two parts: a lower flow of coarse fragments that moves along the ground, and a turbulent cloud of ash that ascends above the basal flow. Ash may fall from this cloud over a broad area downwind from the pyroclastic flow.
These flows demolish almost everything in their path. With speeds usually greater than 80 km per hour pyroclastic flows knock down, smash, bury or carry away almost all objects and structures in their path. The severe temperatures of rocks and gas inside pyroclastic flows can ignite fires and melt snow and ice.
Pyroclastic flows diverge significantly in size and speed; relatively small flows move less than 5 km from a volcano can destroy buildings, forests, and farmland. On the borders of pyroclastic flows, death and serious injury to people and animals may due to burns and inhalation of hot ash and gases.
Lahars
It is a hot or cold mixture of water and rock fragments that flows down the slopes of a volcano and usually enters a river valley. It is sometimes referred to as "debris flows", mainly in the Cascades. Lahars normally occur on or near strato volcanoes. Lahar looks like a roiling slurry of wet concrete, and as it moves downstream, the size, speed, and amount of material carried can continually changes. The first flow may be comparatively small, but it may grow in volume as it enters and incorporates everything in its path – rocks, soil, vegetation, and even buildings and bridges.
Eruptions may generate lahars by melting snow and ice or by ejecting water from a crater lake. Pyroclastic flows can produce lahars when extremely hot, flowing rock debris erodes, mixes with snow and ice as it travel rapidly down steep slopes.
Lahars can also be formed due to the high-volume or long-duration rainfall occurs during or after an eruption. On steep slopes, rainwater can easily erode and move fine-grained, loose volcanic sediment and form slurry, mainly if vegetation has not had time to grow back on recent volcanic deposits.
Large lahars can squash, grind, bury, or carry away nearly everything in their paths. Buildings and valuable land may be partially or completely buried. Lahars can also trap people in regions susceptible to other hazardous volcanic activity, particularly if the lahars leave fresh deposits that are too deep, too soft, or too hot to cross.
Landslides
These are large masses of wet or dry rock and soil that fall, slide, or flow very quickly under the force of gravity. It generally creates as massive rock falls or avalanches, which break up during movement into fragments ranging from small particles to huge blocks. If the landside is large enough and contains a high-enough percentage of water and fine material, it may alter into a lahar that can travel as much as 200 km downstream.
These are general on volcanic cones because they are tall, steep, and destabilized by the rise and eruption of molten rock.
Volcano landslides vary in size from less than 1 km3 to more than 100 km3. The large velocity and huge momentum of landslides permits them to cross valley divides and run up slopes numerous hundred meters high.
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