Geog - Tectonic Hazards - Gateway 2

Natania Leong
Flashcards by , created 2 months ago

Phenomena/landforms found at plate boundaries and how they are formed

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Natania Leong
Created by Natania Leong 2 months ago
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Question Answer
Folding Upfolds are called anticline, downfolds are called syncline and sides of folds are limbs Increasing compressional forces exerted on one limb of a fold may cause rocks to buckle until a fracture forms. The limb may then forve forward to ride over the other limb.
Fold mountains At a convergent plate boundary, two continental plates or one continental plate and one oceanic plate collide. Compressional forces exerted on the two plates causes the rock strata on the continental plate to be compressed and pushed together, causing massive bending and folding of the Earth's crust. Over a long period of time, the layers of continental crust gets contorted, buckle and fold. The rock strata eventually gets pushed up and uplifted to form highlands known as fold mountains. Rocky Mountains, Alps, Himalayas
Distribution of fold mountains Young fold mountains are mostly located along convergent plate boundaries where two continental plates collide or where one continental plate and one oceanic plate collide. Old fold mountains are mostly located far away from convergent plate boundaries (e.g. Ural Mountains in inland Russia) Two major fold mountain belts are the Circum Pacific Belt (fringes western part of Pacific Ocean, Rocky and Andes Mountains) and the Alpine-Himalayan Belt (Morocco in North Africa [Atlas Mountains] through Southern Europe [Alps], across Turkey and Iran, all through to northern part of South Asia [Himalayas] and Southeast Asia [Barisan Mountains])
Normal Fault Cause by tension, usually found along divergent plate boundaries Forms when lithosphere is pulled apart by tensional forces Vertical or near-vertical displacement of ricks: one block lowered relative to the adjacent block Forms steep-sided fault cliff which varies in height - from a few metres to hundreds of metres
Rift Valleys At divergent plate boundaries, two plates are pulled apart. Tensional forces from opposite ends of the crust pull the rocks within the area away from each other. Tensional forces cause normal faults to appear. As the crusts on either side of the normal faults pull apart, the central block of crust in between sinks relative to side blocks to form a steep-sided lowland known as a rift valley. Rhine Valley, Hutt Valley, East African Rift Valley, Dead Sea Rift
Block Mountains At divergent plate boundaries, two plates are pulled apart. Tensional forces from opposite ends of the crust pull the rocks within the area away from each other. Tensional forces cause normal faults to appear. As the crusts on either side of the normal faults pull apart, the side blocks or rock sink relative to the central block of crust, leaving behind a block mountain. Vosges, Sierra Nevada, Black Forest
Distribution of Block Mountains and Rift Valleys Mainly found near or along plate boundaries. Along divergent plate boundaries: East African Rift Valley formed at the divergent plate boundary between the African Plate and the Arabian Plate Sometimes formed away from present-day plate boundaries due to past locations of plate boundaries. Vosges and Black Forest formed at the divergent plate boundary between North American Plate and Eurasian Plate
Volcanism and Volcanicity Volcanism is the process by which solid, liquid or gaseous materials (e.g. magma, gases, ash, dust, cinders, volcanic bombs) are forced upwards into the earth's crust or ejected onto the Earth's surface. Volcanicity is the state or quality of being volcanic. Volcanic material: lava, gases (steam, carbon dioxide, sulphur dioxide) and solid materials (ash, dust, cinders and volcanic bombs/pyroclasts)
Volcanoes Terminology Magma: molten rock found in mantle below the earth's surface Lava: magma that is ejected onto the earth's surface Magma chamber: reservoir of magma beneath earth's crust Vent: opening on earth's surface where magma extrudes Crater: depression at top of volcano through which volcanic material is ejected Caldera: enlarged crater (diameter > 1km) Pipe: central passageway joining the vent to the crater
Stratovolcanoes High-silica viscous acid lava solidifies easily in the pipe, blocking the passageway. This prevents rising magma and trapped gases from escaping, building up tremendous pressure beneath. When increasing pressure beneath can no longer be contained, pyroclasts will be explosively erupted and settle near the vent. Acid lava next escapes and flows over the pyroclasts to form another layer. Before long, the viscous acid lava solidifies in the pipe again and the whole cycle repeats. Acid lava may be extruded through secondary pipes on sides of volcanoes to form socondary cones. Over time, repeated violent eruptions of pyroclasts, followed by outpouring of acid lava, builds up a stratovolcano with steeper slopes at the top and gentle slopes at the base. During a violent eruption, the crater of the volcano may be blown off, causing sides of crater to cave inwards, forming a caldera. Sometimes, vents may be blocked, forcing magma to be extruded through secondary vents to the surface, causing secondary cones to develop over time. e.g. Mount Pinatubo, Philippines
Shield volcanoes Commonly found near divergent plate boundaries, where rising magma is directly extruded from the mantle. Less viscous, fluid basic lava flows easily and spreads over a larger area before solidifying, resulting in the build-up of a shield volcano with gentle slopes. As low-silica lava trap lesser gases, the resultant eruptions are generally non-explosive with little pyroclastic material ejected. Over time, successive eruptions of lava flows builds up the base of the shield volcano. e.g. Mount Washington in USA
Distribution of Volcanoes Generally concentrated along plate boundaries where plates converge, diverge or slip past each other. Pacific Ring of Fire/Circum Pacific Belt: horseshoe-shaped around the Pacific Plate Alpine-Mediterranean Belt: African Plate and Eurasian Plate (Vesuvius) Mid-Atlantic Zone: plate boundary in the middle of the Atlantic ocean East African Rift Valley Zone: east of African continent (African and Arabian Plate)
Risks of Living in Volcanic Areas Destruction by volcanic materials: deaths, injuries and damage to property, infrastructure and natural environment - hot lava and fluid low-silica lava flows -fast moving pyroclastic flows - inhalation of toxic gases and hot ash -impact of volcanic bombs Pollution (ash): large quantities of volcanic ash and dust particles ejected can: disrupt human activities, block sunlight, suffocate crops and cause severe respiratory problems for people and animals and release of toxic gases may suffocate human and animal life
Benefits of Living in Volcanic Areas [Environment] Fertile Soil: weathering of volcanic material: fertile volcanic soil: suitable for farming [Environment] Precious Stones & Minerals: found in volcanic rocks: extraction after millions of years. requires upper layers of volcanic rock to be eroded over time in order for extraction to be possible [Economic] Tourism: Natural tourist attractions: appreciation of scenic volcanic landscapes, hiking, camping, history museums on volcanic sites: tourism multiplier effect: source of revenue for locals and government. volcanic areas with hot springs form health resorts [Economic] Geothermal Energy: derived from heat of earth's crust. groundwater heated by hot permeable rocks in magma: can be harnessed to drive turbines and generate electricity
Transform Fault Caused when adjacent blocks of rocks slide past one another horizontally along the fault line. Horizontal displacement of rock along visible fault line takes place (San Andreas)
Earthquakes Focus: the source, where seismic waves radiate out from a point of sudden energy release Epicentre: point on the earth's surface directly above the focus; seismic waves are strongest Seismic waves: an elastic wave of energy generated by an earthquake which travel either along/near the earth's surface or through the earth's interior Magnitude: amt of energy released Seismograph: records the seismic waves released by an earthquake Richter Scale: shows the amount of energy released by the earthquakes (from 0 - 9)
Earthquakes -- Richter Scale 1-2: only detected by seismographs (tremor) 2-3: felt by a few people near the epicentre/tremor 3-4: little damage to structures, hanging objects swing 4-5: minor damage (cracks in walls) felt by many people, stationary cars can rock 5-6: shocks can be damaging to poorly constructed buildings, furniture moves, walking is difficult 6-7: many structures collapse, cracks appear in the ground, difficult to stan during the earthquake 7-8: severe damage, most buildings collapse 8-9: destruction over a wide area, landslides can be common > 9: destruction can impact thousands of kilometres of land
Factors affecting the extent of damage caused by earthquakes: Magnitude (biggest) The higher the magnitude of an earthquake as indicated on the Richter scale, the higher the likelihood of damage and the wider extent of damage is expected in terms of damage to infrastructure and casualties.
Factors affecting the extent of damage caused by earthquakes: Density of population and built-up area The higher the population density in an area, the more damage is expected in terms of casualties. The more densely built-up an area, the more damage is expected in terms of cost of damage to property and services.
Factors affecting the extent of damage caused by earthquakes: level of preparedness The amount of preparation (e.g. evacuation plans, trained rescue workers, range of action plans, earthquake monitoring) taken by the government and citizens makes a significant difference to earthquake impact. Low level of preparedness for an earthquake occurrence: more earthquake damage.
Factors affecting the extent of damage caused by earthquakes: Distance from epicentre The epicentre is the point on the earth's surface directly above the focus, which is the point of sudden energy release, thus the greatest intensity of the earthquake is felt at the epicentre. The release of earthquake energy in the form of seismic waves are felt most strongly at the epicentre, becoming less strong as the seismic waves travel further away and spread out from the focus. Thus places near epicentre: more damage ** earthquake in Christchurch, New Zealand in 2011: epicentre was in a town a few km away from the city centre. As a result, the city suffered more damage than areas further away from the city.
Factors affecting the extent of damage caused by earthquakes: Time of occurrence The time of day of the earthquake occurrence determines the location and activities of the people. Thus if an earthquake occurs at night, when most people are sleeping, more people will be stuck in their homes and more deaths will occur: more damage
Factors affecting the extent of damage caused by earthquakes: Type of soil/geology of epicentre Places sitting on rocks, soil or sediments that are loose and unconsolidated: seismic waves are amplified and this results in greater damage when earthquakes occur. Liquefaction also affect buildings when the ground becomes unstable and soil flows like a liquid. ** Christchurch 2011: many houses were abandoned because of liquefaction
Factors affecting the extent of damage caused by earthquakes: Depth of focus Shallow focus earthquake: seismic waves reach the earth's surface more quickly: greater impact on land: wider extent of damage
Factors affecting the extent of damage caused by earthquakes: Infrastructure type and design Old buildings and infrastructure (e.g. bridges, roads) are made of flimsy construction materials: more damage during earthquakes
Distribution of Earthquakes Found at any plate boundary, most frequent at convergent plate boundaries. Earthquake-prone areas coincide quite closely with those affected by volcanic activity. Circum Pacific Belt: coincides with oceanic trenches and subduction volcanoes Alpine-Himalayan Belt: coincides with the belt of young fold mountains stretching from the Himalayas to the Alps and Mediterranean region Mid-Atlantic region: coincides with volcanoes and mid-oceanic ridge (Mid-Atlantic Ridge) East African Rift Valley: coincides with diverging plates, rift valleys, block mountains and rift volcanoes
Hazards Associated with Living in Earthquake Zones: Tsunamis Unusually large seismic sea waves generated by an earthquake near or in the sea. may be formed by: movement of sea floor during a large earthquake at subduction zones, underwater volcanic eruption, underwater landslide, a landslide above sea level which causes materials to plunge into the water. Keyword: uplift of seafloor Tsunamis can travel long distances and cause widespread destruction at coastal areas when it sweeps, causing massive flooding and damage to property, infrastructure, cropland as well as casualties.
Hazards Associated with Living in Earthquake Zones: Disruption of services An earthquake can disrupt services such as the supply of electricity, gas, etc. ** 1985 earthquake in Kobe, Japan, disrupted electricity, gas and water to about a million residents of Kobe city's 1.4 million residents
Hazards Associated with Living in Earthquake Zones: Landslides Landslides: rapid downslope movements of soil, rock and vegetation. Mudflows may also occur when there is heavy rainfall.
Hazards Associated with Living in Earthquake Zones: Destruction of property/infrastructure Earthquakes can cause destruction of many homes: people may be homeless and displaced after the disaster Earthquakes may cause cracks to form in infrastructures such as roads or bridges: transportation can be disrupted as it is unsafe to use the damaged roads
Hazards Associated with Living in Earthquake Zones: Loss of lives earthquakes and their associated hazards often threaten the lives of those living in earthquake zones, resulting in injuries and fatalities ** Aceh-Andaman, Indonesia, December 2004, magnitude 9.2 earthquake: estimated 228 000 deaths, 1.7 million people displaced, most powerful tsunami in the Indian Ocean recorded