The planet we live on: The beginnings of the Earth Sciences

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Figure 5.11: Landslide triggered by the El Salvador earthquake in 2001.joints, bedding and other slippage surfaces) and the pressure of the water in the porespaces (the pore water pressure). Slopes are more prone to fail if they have beensteepened by human activity or by erosion of material from the foot of the slope, if<strong>we</strong>aknesses have been attacked by <strong>we</strong>athering, or if they become waterlogged duringstorms. In these circumstances, a small amount of extra stress can cause slopes to failand collapse. Near vertical slopes can collapse by toppling, but most fail by simplysliding downwards, usually breaking up into debris, large and small. Such debris canbe carried a long way, particularly if there is enough water for it to become a slurry.Mudflows and debris flows usually begin as landslides; debris flows carry boulderswhilst mudflows are mostly formed of finer material, but both can be devastating, asshown in Figure 5.11. See the ‘Landslide through the window’ ‘thought experiment’ andthe ‘Sandcastles and slopes: what makes sandcastles and slopes collapse?’ activity athttp://www.earthlearningidea.com.Catastrophic Earth processes only become hazards when they affect people, as they clearlydid in the 2001 El Salvador earthquake (Figures 5.1 and 5.11), so if an Earth process hasa devastating effect on a wilderness area, it is not classed as a hazard because there is no117
isk to humans. <strong>The</strong> amount of risk caused by geological hazards, or geohazards, oftendepends upon the types of human activities involved, whilst people often increase theirrisk by their behaviour. Humans construct settlements and large scale building projectsin geologically hazardous areas for a wide variety of reasons, including good access, goodagriculture, or lack of other available land. Risk is increased by population density; themore people in a vulnerable area the greater the loss of life that can result.Geohazard risk is reduced by taking a series of actions: first the risk should be assessedand evaluated; then if there has to be construction in risky areas, buildings and othercivil engineering projects should be built as safely as possible; then mechanisms shouldbe put in place to monitor and forecast future potential hazards; finally plans should bemade to protect the human population during and after a geohazardous event.<strong>The</strong> first stage of preparing for geohazardsis to assess the hazard and possibly to preparea geohazard map, like that in Figure5.10. It is fairly easy to assess tsunamirisk - any low-lying area in a tsunamiproneregion is in danger; it is relativelyeasy to map volcanic risks, since the presenceof volcanic materials from the recentpast is good evidence that they may be depositedagain, and there may even be his-Figure 5.12: Buildings that did not resist theMexico City earthquake of 1985.torical evidence of past events. Mappinglandslide danger is more difficult, since anysteep slope may be prone to landslides, buttechniques involving careful examination ofrocks and evaluation of earthquake potentialcan be effective in producing landslidegeohazard maps. It is, ho<strong>we</strong>ver, very difficultto produce good local earthquake geohazardmaps, since so many variables are involved, including the intensity of the earthquakeand the strength of the subsurface rocks.If building has to take place in geohazardous areas, then the constructions should behazard-resistant. Many countries in areas prone to geohazards have building codes, so thatin earthquake-prone areas, buildings are constructed to be able to flex and not fractureduring earthquakes, they are given sturdy foundations and use strong building materials.Older buildings can be ‘retrofitted’ to make them more earthquake-resistant - the objectiveis not for buildings to remain completely undamaged by a major earthquake, but to tomake them resistant enough for their inhabitants to survive. Unfortunately in manydeveloping countries, building codes are not enforced for a range of reasons, includingexpense and lack of suitable infrastructure, so much construction in developing regionsmay be affected by geohazards in the future (as in Figure 5.12). In tsunami-prone areas,buildings of concrete are more likely to survive than buildings made of local materials.<strong>The</strong> safest way of constructing buildings safe from landslides is not to build them on orbeneath slopes. Volcanic eruptions of most violent volcanoes are infrequent, and volcanic118
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Basic Books in ScienceBook 6<strong
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BASIC BOOKS IN SCIENCE- a Series of
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BASIC BOOKS IN SCIENCE- a Series of
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Looking ahead - If you came across
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3.2 Plate tectonics (20th Century)
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1.30 Coal seams in an opencast coal
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3.4 Alfred Wegener, the polar explo
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5.14 A GPS remote volcano monitorin
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Figure 1.2:minerals.A sandstone roc
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Even diamond can have different col
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Figure 1.8: A red garnet crystal in
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Figure 1.12: Crystals of minerals i
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Hematite, Fe 2 O 3 - earthy red, me
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Figure 1.17: Sedimentary rocks show
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Figure 1.20: A close up view of a p
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Figure 1.26: Ancient wave ripple ma
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Figure 1.30: Coal seams in an openc
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Figure 1.32: Close up view of a pie
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Figure 1.35: A fossil colonial cora
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Figure 1.38: Fossil ammonites, indi
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Figure 1.39: ‘Massive’ igneous
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Figure 1.41: A close up view of a p
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Figure 1.44: A basalt flow that coo
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Figure 1.47: Deposit of volcanic as
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Figure 1.49: An old slate quarry, s
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Figure 1.51: Slate, a low-grade met
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Figure 1.53: Schist, a medium-grade
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Figure 1.56: Metaquartzite, produce
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Figure 1.58: A region of folded roc
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Figure 1.61: A normal fault. This s
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Figure 1.64: An unconformity. Older
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proper geological maps. Fossils hav
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Cephalopods are not extinct, but th
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Figure 1.68: A shelled cephalopod f
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You can try the rock sequencing pri
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Chapter 2Reading landscapes: how la
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Figure 2.3: Rock fragments loosened
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Figure 2.6: The jo
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Figure 2.10: The m
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are forming them. Similarly the sha
Page 81 and 82: Figure 2.19: This photo was taken f
Page 83 and 84: Figure 2.25: Dinosaur tracks conser
Page 85 and 86: • On coastal sections, whenever p
Page 87 and 88: found evidence that the Earth was a
Page 89 and 90: Figure 3.3: James Hutton, the ‘Fo
Page 91 and 92: Figure 3.5: A page of Wegener’s 1
Page 93 and 94: Figure 3.7: The st
Page 95 and 96: Figure 3.10: The r
Page 97 and 98: Figure 3.13: The m
Page 99 and 100: Figure 3.15: The S
Page 101 and 102: Figure 3.19: An ocean versus contin
Page 103 and 104: Figure 3.23: Map of the major tecto
Page 105 and 106: Figure 3.26: Global temperature cha
Page 107 and 108: Figure 3.29: A computer generated p
Page 109 and 110: Figure 3.31: The
Page 111 and 112: planet extended th
Page 113 and 114: Figure 4.1: William Smith’s geolo
Page 115 and 116: Millionsof yearsago (Ma)01000Some M
Page 117 and 118: ocks whilst the first definite plan
Page 119 and 120: Figure 4.9: The ch
Page 121 and 122: Figure 4.12: The 4
Page 123 and 124: Millionsof years Some Major Earth E
Page 125 and 126: Figure 5.2: Strike-slip movement (r
Page 127 and 128: Figure 5.4: The So
Page 129 and 130: Figure 5.6: An ash eruption rising
Page 131: Figure 5.10: A hazard zone map of t
Page 135 and 136: Figure 5.14: A GPS (global satellit
Page 137 and 138: None of these methods has yet prove
Page 139 and 140: Figure 5.17: A windfarm in Ireland.
Page 141 and 142: Figure 5.19: A beautifully preserve
Page 143 and 144: Another ‘missing link’ find has
Page 145 and 146: Figure 5.22: A dinosaur reconstruct
Page 147 and 148: Figure 5.25: A working aggregate-pr
Page 149 and 150: Figure 5.26: The E
Page 151 and 152: Chapter 6Understanding what geologi
Page 153 and 154: Figure 6.2: A drilling rig used for
Page 155 and 156: When an oil/gas field has been foun
Page 157 and 158: Figure 6.6: Groundwater flowing out
Page 159 and 160: Dam disaster in Italy, when the wav
Page 161 and 162: Figure 6.10: A slab foundation, bui
Page 163 and 164: An example of this is investigation
Page 165 and 166: GlossaryAbsolute age The</s
Page 167 and 168: Carbon capture The
Page 169 and 170: Crustal shortening This results of
Page 171 and 172: Evaporite deposits (or evaporites)
Page 173 and 174: Geophysical survey Using the method
Page 175 and 176: “Integrated waste management” <
Page 177 and 178: Metamorphism The r
Page 179 and 180: Pore spaces (or pores) Gaps bet<str
Page 181 and 182: Saltation Sediment movement by flui
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Suspension Sediment movement by flu
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AcknowledgementsPermission to repri
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Figure 2.3 A scree slope. Photo ID:
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Figure 1.15a Hematite.Figure 1.15b
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Figure 1.28 Dune cross bedding in s
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Figure 3.18 An island arc volcano,
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Figure 5.21 Excavations at the dino
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