CIV TECH 3CS3 Chapter 1

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Civil Engineering Infrastructure Technology
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Jonathan Sussman

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Chapter 1 – Introduction to Natural Hazards - process: meaning the ways in which events, such as volcanic eruptions, earthquakes, landslides, and floods, affect Earth’s surface - the processes we consider to be hazards are natural and derive from the internal heating of Earth and external energy from the Sun - the amount of energy released by natural processes differs greatly (ex. average tornado expends about 1000x as much energy as a lightning bolt does, whereas the volcanic eruption of Mount St. Helens released approx 1 million x as much energy as a lightning bolt - the earth receives approx 1 trillion x as much solar energy than a lightning bolt. Note: a lightning bolt focuses its energy at a point whereas solar energy is spread around the entire globe - events such as earthquakes, tsunami, floods and fires are natural processes that have been occurring on earth’s surface for billions of years - not all hazards are “natural”. Many hazards are caused by people (pandemics, warfare, etc.) Hazard, Risk, Disaster, and Catastrophe - hazard: any natural process that threatens human life or property. The process itself is not a hazard; rather it becomes a hazard only when threatening human interests - risk: the probable severity that a destructive event will occur multiplied by the event’s likely impact on people and property. Integrates hazard and social vulnerability - disaster/catastrophe: events that cause serious injury, ,loss of life, and property damage over a limited time and within a specific geographic area - catastrophes are more massive than disasters and affect a larger number of people and more infrastructure - disasters may be regional or even national in scope, whereas catastrophes commonly have consequences far beyond the area that is directly affected and require huge expenditures of time and money for recovery - The OFDA/CRED International Disaster Database & The Centre for Research on Epidemiology of Disasters defines a disaster must be responsible for a minimum of 30 deaths - no area is considered hazard free - during the past few decades: o annual loss of life = 150 000 o deaths in 2005 alone = 300 000 o financial loss = $50 billion per year o financial loss in 2005 alone = $200 billion - the UN designated the 1990s as the International Decade for Natural Hazards Reduction. The objectives were to minimize loss of life and property damage from natural disasters, but these objectives were not met, rather losses from disasters increased dramatically in the 1990s o Achieving the UN objectives will require education and large expenditures to mitigate specific hazards and contain diseases that accompany disasters and catastrophes - mitigation: used by scientists, planners, and policy makers when describing efforts to prepare for disasters and to minimize their harmful effects. Ex. after floors, water supplies may be contaminated by bacteria, causing disease to spread. To mitigate the effects of this contamination, a relief agency or govt may arrange for portable water treatment plants, disinfect water well, and distribute bottled water Death and Damage Caused by Natural Hazards - in north America, tornadoes and windstorms cause the largest number of deaths each year - loss of life from earthquakes in north America is surprisingly low, largely because of their high standards of building construction however they can cause tremendous property damage - the relation between loss of life and property damage noted above only applies to north America and the fully developed world - natural disasters in most developing countries claim far more lives than comparable events in north America - overall, damage from most hazardous natural processes in Canada is increasing, but the number of deaths from many hazards is decreasing because of better planning, forecasting, warning, and engineering Role of Time in Understanding Hazards - natural disasters are recurrent events; therefore, study of their history provides needed information for risk reduction - knowledge of historic events and the recent geologic history of an area is vital to understanding the hazard and assessing its risk - Geologists have the tools and training to “read the landscape” for evidence of past events, and by linking prehistoric and historic records, they extend our perspective of recurrent natural events far back in time - hazard forecasts and warnings are more accurate if we combine information about the past behaviour of the process with an understanding of present conditions Geologic Cycle - geologic cycle: the four associated sequences of Earth processes: o the tectonic cycle o the rock cycle o the hydrologic cycle o biogeochemical cycles The Tectonic Cycle - tectonic cycle involves the creating, movement, and destruction of tectonic plates, and one cycle can last more than 200 million years - the term tectonic refers to the large-scale geologic processes that deform Earth’s crust and produce features such as ocean basins, continents and mountains - Tectonic processes are driven by forces deep within earth - Tectonic plates: large blocks that form the outer shell of earth; a very large, fault-bounded block of crust and upper mantle that slowly moves on top of the asthenosphere. Tectonic plates form at mid-oceanic ridges and are destroyed at subjection zones Earth’s Lithosphere and Crust - earth comprises several internal layers that differ in composition and physical properties - Outermost or surface layer: lithosphere  stronger and more rigid than deeper material. Average thickness is about 100km, ranges from a few km thick beneath the crests of mid-ocean ridges to 400k, thick beneath continents - Below the lithosphere: asthenosphere  hot layer of relatively low- strength rock that extends to an average depth of about 250km - upper part of the lithosphere: crust  crustal rocks are less dense than the rocks below. - There are two types of crust: oceanic crust and continental crust. Oceanic crust is denser than continental crust. It is also thinner – the ocean floor as an average crustal thickness of about 7km, whereas continental crust is about 30km thick and up to 70 km thick beneath mountainous regions Types of Plate Boundaries - unlike the asthenosphere which is thought to be more or less continuous, the lithosphere is broken into large fragments called lithospheric or tectonic plates that move relative to one another - Processes associated with the origin, movement, destruction of these places are termed plate tectonics. Tectonic plates are formed and destroyed at their margins or boundaries - plate boundaries may be divergent, convergent, or transform - these boundaries are rather broad zones of intense deformation 10s to 100s of km wide that extend through the crust - It is at these boundaries that most earthquakes and active volcanoes occur - Divergent boundaries occur where two plates move away from each other and new lithosphere is produced. Places where this separation occurs are large, underwater mountain ridges known as mid-ocean ridges. By a process known as seafloor spreading, lithosphere breaks or rifts apart along a series of cracks more or less parallel to the ridge crest. Many of the cracks in the underwater rift zone are injected with molten rock, or magma from below. New lithosphere forms as the magma solidifies and is slowly rafted, in a conveyor-belt fashion away from the ridge crust. The tectonic plates on each side of the ridge move apart at 10s of mm to a few 100 mm each year - Convergent boundaries occur where two plates collide head on. Commonly, a higher density oceanic plate is drawn down beneath a lower density continental plate  process called subduction and convergent boundaries of this type are called subduction zones. The oceanic plate heats as it moves beneath the continental plate. At depths of 100km-120km, it reaches temps in excess of 700C and releases H20, CO2 and other gases that rise into the lower part of the continental crust. The superheated gases cause lower crustal rocks to melt and the magma moves slowly up through the crust along fractures. Some of the magma reaches the surface, where it erupts and builds volcanoes. A chain of active volcanoes that have formed from repeated eruptions marks the inboard margin of the Cascadia subduction zone, which extends along the west coast of north America from northern California to central Vancouver island. Well known volcanoes in this chain include: Mount Baker, Mount Rainier, Mount St. Helens, Mount Hood and Mount Lassen. Other important chains of active volcanoes produced b subduction include the Andes of South America, the Aleutian volcanoes in southwestern Alaska, and the volcanoes of Indonesia, Japan and the Caribbean - Subduction adds material to continents. Crustal fragments rafted on the mantle are accreted to the continent. Thick sediments and sedimentary rocks covering the subducting plate are also added to the continent. - If the two colliding plates are continental, they have roughly the same density and it’s more difficult for one to sink beneath the other. In this situation, the plates meet along a continental collision boundary delineated by high, faulted, and crumpled mountains such as the Himalayas - Transform boundaries are when two tectonic plates slide horizontally past each other and the fault along which the movement occurs is known as a transform fault. Most transform faults are located beneath oceans, but some occur on continents. Ex. San Andreas fault in California, where the Pacific plate on the west side is sliding horizontally past the north America plate on the east side Hot Spots - not all tectonic activity takes place at plate boundaries - Volcanoes occur inside a lithospheric plate at locations called hot spots - The rock reaching the surface at hot spots is associated with convection deep within the mantle, the layer between the core and crust that makes up most of the interior of earth. Ex of a hotspot: Yellowstone national park thermal area - Hot spots also occur beneath the Atlantic, pacific and Indian oceans - If a hot spot is anchored in the slowly convecting mantle, it will remain relatively fixed as a lithospheric plate moves over it The Tectonic Cycle and Natural Hazards - as plates slowly move, so do the continents and ocean basins - Most earthquakes and volcanoes that threaten people are near or at plate boundaries - Most tsunami are generated by subduction-zone earthquakes - Landslides are concentrated in mountains produced by plate collisions The Rock Cycle - rocks are aggregates of one or more minerals - rock cycle refers to worldwide recycling of three major groups of rocks, driven by earth’s internal heat and by energy from the sun - The rock cycle is linked to the other cycles, because it depends on the tectonic cycle for heat and energy, the biogeochemical cycle for materials, and the hydrologic cycle for water - Rocks can be classified into 3 general types based on how they are formed: o crystallization of molten rock produces igneous rocks beneath and on earth’s surface. Rocks at or near the surface break down chemically and physically by weathering to form particles known as sediments. These particles range in size from clay to very large boulders and blocks. Sediment formed by weathering is transported by wind, water, ice, and gravity to depositional sites, such as lakes and oceans. When wind or flowing water slackens, ice melts, or material moving under the influence of gravity reaches a flat surface, the sediment is deposited. During burial, the sediment is converted to sedimentary rock by a process called lithification. Lithification takes place by compaction and cementation of sediment during burial. With deep burial, sedimentary rocks may be metamorphosed by heat, pressure, and chemically active fluids into metamorphic rock. Metamorphic rocks may be buried to depths where pressure and temperature conditions cause them to melt, beginning the entire rock cycle again * this is the idealized sequence but there are exceptions The Hydrologic Cycle - hydrologic cycle: the cycling of water from the oceans to the atmosphere, to continents and islands, and back again to the oceans - cycle is driven by solar energy and operates by way of evaporation, precipitation, surface runoff, and subsurface flow - Along the way, water is stored in different compartments, including oceans, atmosphere, rivers and streams, groundwater, lakes and glaciers - Residence time: estimated average amount of time that a drop of water spends in any one compartment, ranges from days in the atmosphere to hundreds of thousands of years in ice sheets - Surface and near-surface water helps move chemical elements in solution, sculpts the landscape, weathers rocks, transports and deposits sediments. It is also the source of the freshwater that makes life on land possible Biogeochemical Cycles - biogeochemical cycle: transfer or cycling of an element or elements through the atmosphere, lithosphere, hydrosphere, and biosphere - Linked with the tectonic, rock and hydrologic cycle - The tectonic cycle provides water and gases from volcanic activity, as well as heat and energy, all of which are required to transfer dissolved solids in gases, aerosols, and solutions - The rock and hydrologic cycles transfer and store chemical elements in water, soil and rock - Elements and chemical compounds are transferred via a series of storage compartments or reservoirs, which include air, soil, groundwater, and vegetation - When a biogeochemical cycle is well understood, the rate of transfer, or flux, among all the compartments is known Fundamental Concepts for Understanding Natural Processes as Hazards 1. Hazards can be predicted through scientific analysis. a. Can be identified and studied using the scientific method. Most disasters can be forecast from past history of similar events, patterns in their occurrence, and types of precursor events 2. Risk analysis is an important element of understanding the effects of hazardous processes a. Considers the probability that a damaging event will occur and the consequences of that event 3. linkages exist between different natural hazards and between hazards and the physical environment a. ex. earthquakes can produce landslides and tsunamis 4. damage from natural disasters is increasing a. the human and economic costs of natural disasters are increasing because of the growth in population, property development in hazardous areas, and poor land-use practices. th Vents that caused limited disastest in the 20 century are causing catastrophes in the 21 century 5. damage and loss of life from natural disasters can be minimized a. by scientific understanding, land-use planning and regulation, engineering and proactive disaster preparedness Hazardous Processes are Natural - humans are apparently a product of the ice ages of the Pleistocene Epoch, which started about 2.6 million years ago - The Pleistene epoch was a time of large fluctuations of climate – from cold, harsh glacial conditions as recently as 12, 000 years ago to the relatively benign interglacial conditions we enjoy today - adjusting to harsh and changing climatic conditions has been necessary for our survival from the very beginning - hazardous earth processes are natural and thus are not the direct result of human activity - land-use changes, such as urbanization and deforestation, may increase the frequency or amplify the effects of some processes - some hazards are completely beyond our control (ex. earthquakes) - best approach is to identify hazardous processes and delineate the geographic areas where they occur. Every effort should be made to avoid putting people and property in harm’s way, especially for those hazards that we cannot control (ex. earthquakes) Prediction and Warning - if we know the probability and the possible consequences of an event at a particular location, we can quantify the risk of the event, even if we cannot accurately predict when it will occur - damage inflicted by a natural disaster can be reduced if the event can be forecast and a warning issued by: - identifying the location of a hazard - determining the probability that an event of a given magnitude will occur - Identifying any precursor events, forecasting the event, and issuing a warning Location - major zones of earthquakes and volcanic eruptions have been identified by mapping (1) where earthquakes have occurred historically, (2) areas of young volcanic rocks, and (3) locations of active and recently active volcanoes Probability of Occurrence - probabilities of rare events, within a specific region are much more difficult to estimate and are subject to large uncertainties Precursor Events - identification of precursor events helps scientists predict when and where a disaster will happen - Ex. the surface of the ground may creep for weeks, months or years before a catastrophic landslide. Volcanoes sometimes swell or bulge before an eruption accompanied by an increase in earthquake activity in the area. Foreshocks or unusual uplift of the land may precede an earthquake. Forecasting - with some natural processes, it is possible to forecast accurately when a possible damaging event will occur - ex. spring flooding can be predicted by snowmelt and warm wet weather Warning - once a hazardous event has been predicted or a forecast made, the public must be warned - The flow of information leading to a public warning of a possible disaster should move along a predefined path - There have been times when warnings have been made but nothing occurred in the end - Although scientists are not yet able to predict volcanic eruptions and earthquakes accurately, they have a responsibility to publicize their informed judgments - An informed public is better able to act responsibility than is an uninformed public - Ship captains reply on weather advisories all the time - Ex. warning was made that a volcanic eruption will occur in the Mammoth Lakes area. The predicted eruption didn’t occur but the advisory led to the development of evacuation routes and a consideration of disaster preparedness making the community better informed - Forecasts and warnings are useful only if they provide people adequate time to respond in an appropriate manner. A minimum of several hours of warning is required in most instances, and much more time is needed if evacuation of urban areas is required - Hazardous processes are open to risk analysis; which considers both the probability that a damaging event will occur and the consequences of that event. Ex. if we were to estimate that in any given year, Vancouver has a 1% change of a moderate earthquake, and if we know the consequences of that earthquake in terms of loss of life and damage, we can then calculate the risk to society - The risk of a particular event is defined as the product of the probability of that event and the consequences should it occur. Consequences include injury, death, property damage, and secondary effects such as lost economic activity. In any risk assessment, it’s important to calculate risks for various possible scenarios (ex. a large earthquake has a lower probability than a small one, but its consequences will be greater) - Determining acceptable risk are difficult because individuals, social groups, and countries have different attitudes about what level of risk is acceptable to them. It also depends on the situation. people have some control over the level of risk they are willing to accept by choosing where they live. Individuals must weigh the pros and cons of living in a particular area and decide whether or not it is worth the risk. They should consider factors such as the frequency of damaging events, potential damage the events could cause, and extent of the geographic area at risk - Population growth and urbanization have accelerated in recent centuries, and today billions of people live in areas vulnerable to damage by hazardous earth processes - Also, over time we’ve learnt to over depend on technology - Inequities in health, education and wealth between developed and developing countries also relate. When a disaster happens in a densely populated area in a developing country, the consequences are likely to be catastrophic whereas if the same event were to happen in a fully developed country, far few people would be injured/killed but the economic cost could be huge Examples of Disasters in Densely Populated Areas - Mexico City was hit with an 8.0 magnitude earthquake in 1985 killing 10,000 people - Izmit, Turkey was hit with an earthquake in 1999 killing 17,000 people because it happened in a densely populated area where m any buildings are poorly constructed and unable to withstand strong shaking - Hurricane Katrina in 2005 Population Growth - the world’s populati
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