A2 GEOGRAPHY REVISIONHAZARDOUS ENVIRONMENTS

9.1 HAZARDOUS ENVIRONMENTSRESULTING FROM TECTONIC MOVEMENT

KEYTERMSANDDEFINITIONSActive margin is the edge of a tectonic plate where sea-floor spreading or subduction is occurring. Ash fallout is the deposition of fine-grained material following a volcanic eruption. Benioff zone is a narrow zone of deep earthquake foci at a subduction zone. Caldera is a large basin in a volcanic area where surface rocks have subsided into the molten magma below. Continental crust is that part of the Earth’s crust that forms the continents.

KEYTERMSANDDEFINITIONSEarthquakes are a series of shockwaves / vibrations and tremors caused by sudden release of pressure along fault lines, and usually associated with plate boundaries. Hot spot is a relatively small area where magma rises through a continental or ocean plate. As the plate moves across the hot spot a chain of volcanoes may form. Lava is molten magma that has reached the earth’s surface. It may be liquid, or may have solidified. Lava flow is the movement downslope from a volcanic crater or fissure of molten rock (lava). As the lava flows it cools, most rapidly at the base and surface, and begins to solidify.

KEYTERMSANDDEFINITIONSLithosphere is the outermost layer of the Earth comprising the crust and part of the mantle. Magma is molten rock within the Earth; when it reaches the surface it is called lava. Mercalli Scale is a scale of earthquake intensity based on descriptive data. Mid-ocean ridges are lines of mainly mountains formed where two ocean plates are separating. Nuee ardente is a mass of hot gas, superheated steam and volcanic dust that travels down the sides of a volcano as a ‘glowing avalanche’ following a volcanic eruption.

KEYTERMSANDDEFINITIONSOceanic crust is that part of the crust underlying the oceans. It is basaltic in composition. Pyroclastic flow is a fast-moving cloud of extremely hot gas, ash and rock fragments, which can reach temperatures of about 1 000 °C and travel at speeds of up to 700 km/h. Richter Scale is an open-ended scale to record magnitude of earthquakes. Subduction zone is the area where one plate slides beneath another; a zone of earthquakes and melting.

KEYTERMSANDDEFINITIONSTephra is solid material, whatever its size, ejected from a volcano, and often called pyroclastic material. Transform fault is where two plates slide past each other; like a tear fault on a larger scale. Tsunamis are sea-surface waves created by submarine earthquakes. In deep oceans they appear insignificant in height, but as they approach the shore friction with the shallowing sea bed causes an increase in amplitude to several metres. They are sometimes called tidal waves, but they have no connection with tides. Tuff refers to fine particles of tephra (up to 4 mm in diameter). Volcanic bomb is a fragment of molten lava (over 4 mm in diameter) thrown from a volcano.

TOPICSUMMARY Most of the world’s earthquakes occur in clearly defined linear patterns. ● An earthquake is a violent shock within the Earth that releases huge amounts of energy as shockwaves or seismic waves. ● In areas of active earthquake activity the chances of an earthquake increase with increasing time since the last earthquake. ● The strength of an earthquake is measured by the Richter Scale and the Mercalli Scale.

TOPICSUMMARYThe extent of earthquake damage is influenced by the strength and depth of the earthquake, number of aftershocks, population density, the type of buildings, time of day, distance from the epicentre, type of rocks and sediments, secondary hazards and level of economic development. ● Most earthquakes occur with little if any advance warning. ● Most problems are associated with loss of life and damage to buildings, structures and transport systems.

TOPICSUMMARYHuman activities can trigger earthquakes, or alter the magnitude and frequency of earthquakes, by increasing crustal loading, underground disposal of liquid wastes and underground nuclear testing and explosions.● The main ways of dealing with earthquakes include better forecasting and warning; and building design, building location and emergency procedures. ● Most volcanoes are found at plate boundaries, although some occur over hot spots. ● Volcanoes that are found at mid-ocean ridges, or hot spots, tend to produce relatively fluid basaltic lava, as in the cases of Iceland and Hawaii.

TOPICSUMMARYVolcanic hazards can be divided into six main categories: lava flows, ballistics and tephra clouds, pyroclastic flows, gases and acid rain, lahars (mud flows) and glacier bursts (jokulhlaups). ● The strength of a volcano is measured by the Volcanic Explosive Index (VEI). ● Scientists are increasingly successful in predicting volcanic eruptions. ● The main ways of predicting volcanic eruptions include use of seismometers to record swarms of tiny earthquakes, chemical sensors to measure increased sulphur levels, lasers to detect the physical swelling of the volcano and ultrasound to monitor low-frequency waves in the magma. ● People live in volcanic areas because of the benefits they bring (fertile soil, new land, tourism, chemicals).

ADDITIONALWORK1. Describe and account for the distribution of either volcanoes or

earthquakes. 2. Outline the range of hazards associated with volcanic eruptions. 3. Explain the factors that affect the impact of earthquakes. 4. Comment on ways in which earthquake risk is managed. 5. In what ways is it possible to manage volcanic hazards? 6. What are the hazards associated with tsunamis and how far is it possible to

manage them? 7. Outline the impacts of either volcanoes or earthquakes. 8. To what extent can the impacts of volcanoes or earthquakes be managed? 9. To what extent is it possible to predict a volcanic eruptions and b

earthquakes?

SUGGESTEDWEBSITEShttp://volcano.und.nodak.edu/vwdocs/current_volcs/ montserrat/montserrat.html for current volcanic activity. www.montserrat-newsletter.com for the Montserrat newsletter. http://news.bbc.co.uk/1/hi/8540289.stm to read about the Chile earthquake, access a map and find other links.Go to http://news.bbc.co.uk/1/hi/world/americas/8543324.stm and answer the question ‘Why did the Haiti earthquake have a greater impact than the Chile earthquake?’

SUGGESTEDWEBSITESwww.cnn.com/SPECIALS/2010/haiti.quake/ for a CNN special on Haiti. www.bbc.co.uk/news/world-asia-pacific-12769741 Japanese tsunami: good on Miyako City. www.bbc.co.uk/news/world-asia-pacific-12778798 Japanese tsunami: aerial footage of Fukushima. www.bbc.co.uk/news/world-asia-pacific-12709850 Japanese tsunami: flat low-lying Sendai. www.bbc.co.uk/news/world-asia-pacific-12709856 Japanese tsunami: whirlpool.www.bbc.co.uk/news/world-asia-pacific-12735023 Japanese tsunami: people watching up close.