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MODULE 1

1. EARTH SCIENCE

Earth science or geoscience is an all-encompassing term that refers to the fields of science dealing with planet Earth. It can be considered to be a branch of planetary science, but with a much older history. T The formal discipline of Earth sciences may include the study of the atmosphere, hydrosphere, lithosphere, andbiosphere.Earth Science is the study of the Earth and its neighbors in space. It is an exciting science with many interesting and practical applications. Some Earth scientists use their knowledge of the Earth to locate and develop energy and mineral resources. Others study the impact of human activity on Earth's environment and design methods to protect the planet. Some use their knowledge about Earth processes such as volcanoes, earthquakes and hurricanes to plan communities that will not expose people to these dangerous events.

BRANCHES:Geology is the primary Earth science. The word means "study of the Earth". Geology deals with the composition of Earth materials, Earth structures, and Earth processes. It is also concerned with the organisms of the planet and how the planet has changed over time. Geologists search for fuels and minerals, study natural hazards, and work to protect Earth's environment. Meteorology is the study of the atmosphere and how processes in the atmosphere determine Earth's weather and climate. Oceanographyis the study of Earth's oceans - their composition, movement, organisms and processes. Astronomy is the study of the universe.

Today we live in a time when the Earth and its inhabitants face many challenges. Our climate is changing and that change is being caused by human activity. Earth scientists recognized this problem and will play a key role in efforts to resolve it. We are also challenged to: develop new sources of energy that will have minimal impact on climate; locate new sources of metals and other mineral resources as known sources are depleted; and, determine how Earth's increasing population can live and avoid serious threats such as volcanic activity, earthquakes, landslides, floods and more. These are just a few of the problems where solutions depend upon a deep understanding of Earth science.

2. BRANCHES OF GEOLOGY

Geology is a study of the Earth and its history as recorded in the rocks. The study of geology involves understanding the relationship between the rocks of the crust of the Earth and envelopes of air and water. Geology is a study of processes that form continents and ocean basins, mountains and oceanic deeps, glaciers and lakes, sand bars and rocky cliffs, and deposits of minerals, coal and oil and gas. Geologists study rocks to determine what the Earth was like thousands, millions, and billions of years ago. Geologists study volcanoes, lavas, earthquakes, and landslides. They discover how our mineral deposits formed. They give us theories on how the Earth was formed, how it developed, and what the core of the Earth is like. The Earth is about 4.5 billion years old. Geology tells us how the Earth has changed and continues to change. Hills are worn down to form lowlands that may be covered by the sea. Millions of years later, rocks from under the sea may be raised up to form high mountains. The Earth is the geologists laboratory.

Two broad areas: 1. Historical Geology – origins and evolution of the Earth, its continents, atmosphere and life

2. Physical Geology – rocks, minerals and the processes that affect them.

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There are a broad range of sub-disciplines within geology many of which are related to other sciences while others have a direct influence on human activity : (i) Physical Geology (ix) Economic Geology (ii) Crystallography (x) Mining Geology (iii) Mineralogy (xi) Civil Engineering Geology (iv) Petrology (xii) Hydrology (v) Structural Geology (xiii) Indian Geology (vi) Stratigraphy (xiv) Resources Engineering (vii) Paleontology (xv) Photo Geology (viii) Historical Geology

Physical Geology As a branch of geology, it deals with the “various processes of physical agents such as wind, water, glaciers and sea waves”, run on these agents go on modifying the surface of the earth continuously. Physical geology includes the study of Erosion, Transportation and Deposition (ETD). The study of physical geology plays a vital role in civil engineering thus: (a) It reveals constructive and destructive processes of physical agents at a particular site. (b) It helps in selecting a suitable site for different types of project to be under taken after studying the effects of physical agents which go on modifying the surface of the earth physically, chemically and mechanically.

Crystallography As a branch of geology, it deals with ‘the study of crystals’. A crystal is a regular polyhedral form bounded by smooth surfaces. The study of crystallography is not much important to civil engineering, but to recognize the minerals the study of crystallography is necessary.

Mineralogy As a branch of geology, it deals with ‘the study of minerals’. A mineral may be defined as a naturally occurring, homogeneous solid, inorganically formed, having a definite chemical composition and ordered atomic arrangement. The study of mineralogy is most important. (a) For a civil engineering student to identify the rocks. (b) In industries such as cement, iron and steel, fertilizers, glass industry and so on. (c) In the production of atomic energy.

Petrology As a branch of geology it deals with ‘the study of rocks’. A rock is defined as “the aggregation of minerals found in the earth’s crust”. The study of petrology is most important for a civil engineer, in the selection of suitable rocks for building stones, road metals, etc.

Structural Geology As a branch of geology, it deals with ‘the study of structures found in rocks’. It is also known as tectonic geology or simply tectonics. Structural geology is an arrangement of rocks and plays an important role in civil engineering in the selection of suitable sites for all types of projects such as dams, tunnels, multistoried buildings, etc.

Stratigraphy As a branch of geology it deals with ‘the study of stratified rocks and their correlation’.

Paleontology As a branch of geology, it deals with ‘the study of fossils’ and the ancient remains of plants and animals are referred to as fossils. Fossils are useful in the study of evolution and migration of animals and plants through ages, ancient geography and climate of an area.

Historical Geology As a branch of geology, it includes “the study of both stratigraphy and paleontology”. Its use in civil engineering is to know about the land and seas, the climate and the life of early times upon the earth.

Economic Geology As a branch of Geology, it deals with “the study of minerals, rocks and materials of economic importance like coal and petroleum”.

Mining Geology As a branch of geology, it deals with “the study of application of geology to mining engineering in such a way that the selection of suitable sites for quarrying and mines can be determined”.

Civil Engineering Geology As a branch of geology, it deals with “all the geological problems that arise in the field of civil engineering along with suitable treatments”. Thus,

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it includes the construction of dams, tunnels, mountain roads, building stones and road metals.

Hydrology As a branch of geology, it deals with “the studies of both quality and quantity of water that are present in the rocks in different states”(Conditions). Moreover, it includes: (a) Atmospheric water, (b) Surface water, and (c) Underground water.

Indian Geology As a branch of geology, it deals with “the study of our motherland in connection with the coal/petroleum, physiography, stratigraphy and economic mineral of India”.

Resources Engineering As a branch of geology deals with “the study of water, land, solar energy, minerals, forests, etc. fulfill the human wants”.

Photo Geology As a branch of geology deals with “the study of aerial photographs”.

Geochemistry As a branch of science, it deals with geology in such a way that it concerns with the abundance and distribution of various elements and compounds in the earth.

Geophysics As a branch of science, it is related with geology in such a way that it concerns with the constitution of the earth and the nature of the physical forces operating on with in the earth.

Geohydrology As a branch of science, it is related with geology in setting of ground water. In other words, Geohydrology is an “interaction between Geology and Hydrology”.

Rock Mechanics As a branch of science, it is related with geology in dealing with the behaviour of rocks that is subjected to static and dynamic loads (force fields).

Mining Engineering Geology is related to mining engineering in dealing with the formation and distribution of economic minerals and response to fracturing processes. With out the knowledge of structural features of rock masses and mode of occurrence and mineral deposits, a mining engineer cannot determine the method of mining.

3. IMPORTANCE OF GEOLOGY FOR CIVIL ENGINEERING

The role of geology in civil engineering may be briefly outlined as follows: 1. Geology provides a systematic knowledge of construction materials, their structure

and properties. 2. The knowledge of Erosion, Transportation and Deposition (ETD) by surface water

helps in soil conservation, river control, coastal and harbour works. 3. The knowledge about the nature of the rocks is very necessary in tunneling,

constructing roads and in determining the stability of cuts and slopes. Thus, geology helps in civil engineering.

4. The foundation problems of dams, bridges and buildings are directly related with geology of the area where they are to be built.

5. The knowledge of ground water is necessary in connection with excavation works, water supply, irrigation and many other purposes.

6. Geological maps and sections help considerably in planning many engineering projects.

7. If the geological features like faults, joints, beds, folds, solution channels are found, they have to be suitably treated. Hence, the stability of the structure is greatly increased.

8. Pre-geological survey of the area concerned reduces the cost of engineering work.

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4. SCOPE OF GEOLOGY

Engineering Geology has a scope in different fields as outlined below: (a) In Civil Engineering: Geology provides necessary information about the site of

construction materials used in the construction of buildings, dams, tunnels, tanks, reservoirs, highways and bridges. Geological information is most important in planning phase (stage), design phase and construction phase of an engineering project.

(b) In Mining Engineering: Geology is useful to know the method of mining of rock and mineral deposits on earth’s surface and subsurface.

(c) In Ground Water: Resources development geology is applied in various aspects of resources and supply, storage, filling up of reservoirs, pollution disposal and contaminated water disposal.

(d) Land pollution. (e) Nuclear explosion. (f) Oceanography. (g) Space exploration. In each of the above-mentioned fields Geology has to deal

with an integral part of the earth

5. GEOLOGICAL WORK OF WATER

¸ About 71 % of earth surface is covered with water in the form of streams , lakes , rivers , seas and oceans

¸ Small surface water bodies flowing in channels of their own are called as streams.

¸ Many streams flowing through a big area and ultimately joining to form a single major channel of flow is called a river.

Sources of stream water:1. Runoff – Major part of precipitation flowing over and above the surface of the earth through channels .

- Very big source of water for streams and rivers.

2. Sub surface water – water that has infiltrated into the earth is called subsurface water.3. Glacial melt water – Glaciers cover more than 10 % of surface area of the earth. Glacial melt waters contribute a lot to mountainous streams.

River profile:¸ From the place of origin to its final destination in the sea , every river channel is

characterized with a longitudinal profile.

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¸ Highland or Mountainous region where the river originates is called the head region.¸ River flows through gradually decreasing slopes and then through flat lands before it

actually empties into the sea.¸ The place where river enters a sea is called its mouth.

Geological work of streams may be broadly divided into three well defined phases

1. Erosion2. Transportation3. Deposition

Methods of River Erosion:Streams and Rivers are the most powerful agents of erosion. Running water performs erosion in five ways

l Hydraulic Actionl Cavitationl Abrasionl Attritionl Corrosion

Hydraulic action: It is the mechanical loosening and removal of the material from the rocks due to pressure exerted by the running water.The higher- the velocity, the greater is the pressure of the running water on the rock or grains of soil which moves out the parts from the parent body occurring along its base or sides.Potholes may be developed due to hydraulic action.Cavitation:It is particularly observed where river water suddenly acquires exceptionally high velocity such as at the location of a waterfall. It is known that where stream velocity exceeds 12m/sec , the water pressure developed at the impinging points equals vapour pressure.Abrasion: It involves wearing away of the bedrocks and rocks along the banks of a stream or river by the running water. Sand grains, pebbles and gravels ,rock fragments moving along with river water are collectively known as tools of erosion. Attrition: Attrition is the wear and tear of the load sediments by mutual impacts and collusions during their transport. Due to these mutual collusions, the irregularities and

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angularities of the particles are worn out. These become spherical in outline and rounded and polished at the surface.Corrosion:The slow but steady chemical (especially solvent) action of the stream water on the rocks is expressed by the term corrosion. The extent of corrosion depends much on the composition of rocks and also on the composition of flowing water.

Features of stream erosion:Common features developed on the surface of land as a result of river erosion are1. Potholes2. River valleys3. Dip slope4. Water falls5. Stream terracesPotholes: The potholes are generally cylindrical or bowl shaped depressions developed in the river bed by excessive localized erosion by streams. These depressions becomes the spots where pebbles and gravels of the stronger rocks are caught in eddies and thrown into a swirling motion.

River valleys:A valley may be defined as a low land surrounded on sides by inclined hill slopes and mountains. Rivers are responsible for the origin, development and modification of the valleys through well- understood processes of river erosion.

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. Origin of valleyl Rain water flowing as small streamlets produce small gullies in the gently sloping

land surface.l These gullies are incipient valleysl Further erosion deepens and widens the original gully that can accommodate bigger

volumes of water and thus suffers greater erosion which results in the formation of Valley

Valley Deepeningl Valley Deepening – Cutting down of the river bedl It is achieved by cooperative action of all the processes involved in erosion:

hydraulic action, abrasion and chemical action or corrosion.l Lowest level up to which a river can erode its channel is called base level of erosion.

Lengthening of river valley

l Each main stream has its tributaries , the rate of erosion in the main stream is much higher than in the tributaries.

l The tributaries are merged completely with the main valley which results in the extension of main valley.

River CaptureRiver capture is a geomorphological phenomenon occurring when a stream or river is diverted from its own bed, and flows down into the bed of a neighboring stream.Valley Wideningl Direct process – streams cut down their channels and removes the loose soil and

rocks from the banks there by widening the valley directly.l Streams achieve valley widening by an indirect method rather than by direct erosion

alone.l Once a small valley is created , slopes of the valley are exposed to secondary

processes – weathering of all types , rain – wash , soil creep , landslides. l The combined action of these secondary processes loosens the material from the

slopes.l River widens the valley by transporting the materials supplied to them from the

valley slopesGorges: Gorges are very deep and narrow valleys with very steep and high walls on

either side. Length varies from few meters to several kilometres.Canyons:Canyon is a specific type of gorge where layers cut down by a river are stratified and horizontal in attitude.Example : Grand canyon of Colorado (depth 900 to 1800 mts , width – 60 to 60 mts ,

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length – 300 km.)Escarpments and Features:Escarpments are erosional features produced by rivers in regions composed of alternating beds of hard and soft rocks.

Stream erodes the overlying softer rock , fully exposing the underlying hard layer. The resulting slope (angle of inclination of layer with horizontal) is called a dip slope. CUESTA is known as the combined set of escarpment and dip slope occurring adjacently in an escarpment topography. Hog back – It is an outcrop of hard rock having erosional slopes on either side.

Mesa and Butte:These are horizontally layered rocks, having a cap of hard and resistant rocks that have escaped erosion. Large sized caps are called Mesa and small sized isolated patches are called butte. These features result in areas of alternating hard and soft layers exposed to river erosion.Water falls:These are defined as magnificent jumps made by stream or river water at certain specific parts of their course where there is a sudden and considerable drop in the gradient of the channel.In a waterfall, the stream literally falls (instead of flowing) from a considerable height before acquiring normal flow again at a lower level. Obviously, the velocity of water at the point of fall increases tremendously. Successive falls of smaller heights are sometimes referred as rapids and cascades.Stream Terraces: These are bench like ledges or flat surfaces that occur on the sides of many river valleys. From a distance, they may appear as succession of several steps of a big natural staircase rising up from the riverbank. They may be made up of hard rock or of soft rock, but the essential thing is that they look like steps.

Sediment Transport by Rivers

Types of load The load being transported in running water of stream or river are, l The Suspended Loadl The Bed Loadl The Dissolved Load

Suspended LoadFine sand, silt and clay sediments are transported in a state of suspension.Load lifted up in stream are not allowed to touch the base due to eddies caused by turbulence

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Bed LoadHeavier particles of sand, pebbles gravels, cobbles are transported by the method of saltation. Sediment transport method carried out in a series of jumpsDissolved LoadMaterials soluble in water are transported. Eg: Limestone , gypsum , anhydrite , rock salt

Deposition by Rivers

The entire load of a stream or a river will normally remain in transport.when there is a decrease in the load carrying capacity of stream due to whatsoever reason, a part or whole of the load will be dropped down.This process is called deposition of rivers

EX : Fluvial Deposits1. Alluvial fans and cones

These are cone shaped accumulations of stream deposits found at places where stream rushing down from hill slopes with enormous debris to the low land area. Most of the load is spread out in all directions. Slope of deposit is below 10° - Alluvial fan. Slope of deposit 10° to 50° - Alluvial cone.

2. Flood plains:Floodwaters are invariably heavily loaded with sediments of all types. When these

waters overflow the river banks and spread as enormous sheets of water in the surrounding areas, their velocity soon gets checked everywhere due to inequalities of the ground, absence of a well defined channel and many other obstructions. As a consequence, they deposit most of the load as a thick layer of mud, so commonly seen after every major flood. Since such a process may get repeated after intervals, the low lying areas surrounding major rivers are actually made up of varying thickness of flood deposits. These are generally level or plain in nature and extensive in area; hence they are aptly called Flood PlainsTwo major types of flood plains are :1. Convex Flood plains2. Flat flood plains

Convex flood plains - The surrounding areas are located at rather lower levels Compared with the river channel and hence give a convex shape to the deposit in a vertical cross section.

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Flat flood plains -These flood plains appear mostly flat in cross section and are made up mostly of sand and silt sediments.

3. DeltasDeltas are defined as alluvial deposits of roughly triangular shape that are deposited

by major rivers at their mouths, i.e. where they enter a sea. Deltas are quite complex in their structure because of operation of a number of factors during their formation, evolution and modification with passage of time.

4. Channel DepositsMany streams are forced by some natural causes to deposit some of their load along

their river –beds. They are called as channel deposits. Channel deposits includes varied mixture of clays, silts , sand and gravels and occasional boulders.5. River Meandering

When a stream flows along a curved , zig zag path acquiring a loop – shaped course ,it is said to meander. The process of development of zigzag type of channel for itself is called river meandering. Meanders are developed mostly in the middle and lower reaches of major streams where lateral erosion and deposition along opposite banks occur.

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Stream patterns:

l Consequent streams – First streams developed based on the topography of the area.l Subsequent streams – These are tributaries of consequent streamsl Obsequent streams – Tributaries of subsequent streamsl Insequent streams – They are called as irregular streams found to flow in channels

Drainage patterns:The relationship of all these streams with each other and with the region as a whole give rise to the drainage pattern of that area.1. Trellis drainage2. Dendritic drainage3. Radial drainage4. Superimposed drainage5. Antecedent drainage

Trellis drainage – when consequent stream receives a number of subsequent streams from right and left approximately at right angles to its direction of flow.Dendritic drainage – when streams of different types (consequent, subsequent, obsequent) are all fairly common in a regionRadial drainage – This pattern develops in region which are elevated or depressed with reference to topography.Superimposed drainage – it is developed in geologically old and complex folded regions.Antecedent Drainage - streams flowing over a gradually rising block of crust of the earth form the antecedent drainage

6. GEOLOGICAL WORK OF WIND

Air in motion is wind. Wind is one of the three major agents of change on the surface of earth. Winds are born due to non-uniform heating of surface of earth at different places causing differences in atmospheric pressure. The pressure difference so created, makes the atmospheric gases to move from area of high pressure to areas of low pressure in the form of winds.Wind ErosionWind performs erosion by three methods: Deflation, abrasion and attrition.Deflation

It is the process of removal of particles by strong winds is called deflation. It is the

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main process of wind erosion in desert region.Blow Out: Small scale depressionOasis: Deeper depressionAbrasion

Wind becomes a powerful agent for rubbing and abrading when naturally loaded with sand and dust particles. So this type of erosion involves rubbing, grinding and polishing the rock surfaces by any natural agent with the help of its load while passing over the rocks is called wind abrasion. It is responsible for numerous features of erosion on land surface. Example: Pedestal rocks, Yardangs, Ventifacts and desert pavements.Attrition

The sand grains and other particles lifted by winds from different places are carried away to considerable distance. The grains are moving in zigzag manner colliding with one another again and again. The wear and tear of load sediments suffered by them Due to mutual impacts during the transport process is known as attrition. It is primarily responsible for reduction in size of load particles.The intensity of wind erosion by the above 3 processes depends on following factors:a. Nature of regionb. Velocity of wind.c. Duration.Sediment transport of windSources of sediment

Wind is an active agent of sediment transport. A great part of wind load is contributed by dry incoherent regions like sand deserts and freshly ploughed fields.Methods of transporti. Suspension: The light density particles like clay or sand particles may be lifted from ground and carried to higher upper layer where they move along with the wind.ii. Saltation: The heavier and coarse sediments such as sand grains, pebbles and gravels are lifted up periodically during high velocity wind for short distances. They may be dropped and picked up again and again from one place to another.Transporting power of windThe transporting power of wind depends on its velocity, size, shape and density of the particles.Deposition by windAeolian deposits: Load dropped by wind in a particular region may be of very small or of considerable volume. These winds deposits may ultimately take shape of sand form which is known as Aeolian deposits.These are of two types: 1.Dunes

2.Loess1. Dunes: These are variously shaped deposits of sand particles accumulated by wind. Sand dune is defined as broadly conical haep of sand with 2 slopes on both sides. A dune is developed when a sand leading wind come across some obstruction. The obstruction cause check in the velocity of wind. They compel to drop some particles along, against or over the obstruction. Sand dunes show great variation in their shape, size and grouping.

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Crescentic dune caused by windi. Crescentic dunes: A Crescentic dune is characterised by two slopes. The windward is convex in nature. It has a well defined crest. The downward slope has two well defined parts- Slip face and Cusps.

Barchan caused by windBarchans: These are simplest types of crescentic dunes with half moon shaped dunes developed by wind blowing in same direction for considerable length of time.ii. Sigmoidal dunes: A typical sigmoidal dune is characterised with the absence of cusps. A sigmoidal dune is steep sided ridge that extends in a sinuous or S-shaped outline.

Dunes can also be classified into simple, complex and compound groups.a. Simple: It is a single dune of either of the above fundamental types.b. Compound: It is a dune consisting of one or more dunes of same type.c. Complex: It is a group of dunes of different types occurring in close vicinity to each other.

2. Loess: The term loess is used for wind blown deposits of silt and clay grade particles. Typical loess is unconsolidated, unstratified and porous accumulation of particles of the size range of 0.01-0.05 mm in diameter. This size fraction makes almost 40 percent of a particular loess deposit, rest being made up of still finer clay grade material.

LoessEngineering consideration

Dunes may travel for considerable distances in any direction and in the process may bury agricultural lands and forests. Methods to prevent this from happening are:

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1. Establishing contour tracks or belts of vegetation that resist in advancing the sand by checking the velocity.2. Construction of wind breaks or walls around the areas to be protected.3. Loess soil settles down easily and quickly in the presence of moisture. So, these form very dangerous foundation soils.

7. WEATHERING OF ROCKS

Weathering is the breaking down or dissolving of rocks and minerals on Earths surface. Water, ice, acids, salt, plants, animals, and changes in temperature are all agents of weathering. Weathering is the disintegration and decomposition of rocks in situ. Changing temperature, rainfall and rock type have an important influence on the type of weathering occurring. Geologists distinguish between two types of weathering -- nature attacks rocks in one of two ways: – Physical weathering sometimes called mechanical weathering) and Chemical weathering.Physical Weathering

Process of breaking intact rock into smaller grains or chunks (together called detritus) - does not change chemical composition.Grain sizes of detritus:

• Boulders >256mm, Cobbles= 64-256 mm, Pebbles = 2-64 mm, Sand = 1/16 - 2 mm, Silt = 1/256 - 1/16 mm, Mud <1/256 mmTypes of Physical Weathering

JointingWhen rocks are buried deep in the Earth, they are under a great amount of pressure.

As the overburden is removed by erosion, pressure is released.If the rocks are near the surface of the Earth, the rocks react to the release of pressure by forming cracks. These naturally formed cracks are called JOINTS.

Exfoliation

Granites are INTRUSIVE igneous rocks, when the overburden is removed from a granite, the joints that form are often parallel to the surface of the rock. These JOINTS are called exfoliation joints (it’s like peeling the skin off the granite

Frost Wedging

Joints are pried apart by freezing water. • When water freezes it expands by about 9% -this is why pipes break.

Root Wedging

Joints are pried apart by roots. As the root grows the rocks break into pieces.

Salt Wedging

In arid climates, dissolved salt in groundwater crystallizes and grows in open pore spaces in the rock and pushes apart the surrounding grains.

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Thermal expansion and Animals

• When rocks get heated by the sun, they tend to expand. As they expand, they crack and break off, this is called SPALLING.

• Animals can also contribute to the physical weathering of rocks by burrowing, digging and prying rocks apart.Chemical Weathering

• Refers to chemical reactions that alter or destroy minerals when rock comes into contact with water solutions or air.• This process actually changes the chemical composition.Dissolution

• Chemical reactions that actually dissolve the minerals in a rock.

• Primarily salt and carbonates (like calcite)

• Minerals like halite are dissolved rapidly and easily by rainwater.Hydrolysis

• Water chemically reacts with minerals and breaks them down . Slightly acidic water makes it easier. The MOST common type of CHEMICAL weathering. It’s the way we get the two most common sediments on Earth- quartz and clay

2KAlSi3O8 + 2H2CO3 + H2O

K-feldspar + carbonic acid + water

Al2Si2O5(OH)4 + 2K+ + 2HCO3- + 4SiO2

clay + potassium ions + bicarbonate ions + quartzOxidation• The process of losing an electron is called oxidation because this process commonly occurswhen elements combine with oxygen.• The kind of oxidation with which we are most familiar is rusting -- oxidation of iron.• Anytime you see a rusty red color, you can be sure that oxidation is at work there!

Physical and Chemical Weathering Working Together• it is nearly impossible to separate physical and chemical weathering. In fact, they complement each other.• Physical weathering speeds up chemical weathering because it increases the surface area exposed to water and other chemical compounds• Chemical weathering speeds up physical weathering by dissolving part of the rock and making it weaker and thereby easier to break apart and carry away.Spheroidal weathering• Both kinds of weathering happen together more rapidly at the edges of a block than on the surface• This has the result of rounding the blocky, jointed rocks making them more like balls than blocks.• This process is called spheroidal weathering.• Particularly common in granites.

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8. VOLCANOES

Volcanoes: The word “volcano” comes from the little island of Vulcano in the Mediterranean Sea of Sicily. Naturally occurring fissures, conduits, or vents through which hot materials comes out regularly or intermittently are termed as volcanoes. They are a clear result of tectonic activity. The Earth’s crust is broken up into different plates or pieces. They slowly move in different directions making mountains, volcanoes, or deep trenches. Volcanoes occur at both divergent and convergent boundaries and also at hot spots. When plates push together, one plate slides beneath the other (subduction zone). When the plunging plate gets deep enough inside the mantle, some of the rock on the overlying plate melts and forms magma that can move upward and erupt at the Earth's surface. At rift zones, plates are moving apart and magma comes to the surface through volcanic eruption through volcanic eruption. Some volcanoes occur in the middle of ocean that are called hot spots.

Lava is the term used for molten materials molten materials that have reached the ground surface because of a volcanic eruption. Magma is the molten materials that are found below the ground.Parts of volcanoes:-

• The magma that feeds the eruptions pools deep underground in a structure called a magma chamber.

• At Earth’s surface, lava is released through openings called vents.

• Flowing lava in the interior travels through long, pipe like structures known as lava tubes or conduits.

• Conical mound or hill around the point of eruption or mouth of the volcanoe is known as volcanic cone

• Openings of volcanoes at the surface -volcanic craters. In most cases, oval opening in the middle of the cone. Few meters to kilometers in diameter. Craters are up to 500 m across and 200 m deep. Strato volcanoes form secondary craters also. Very large sized craters that have collapsed with passage of time are known as calderas.

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Vent- An opening allowing the passage of air.Ash Cloud- The powdery residue left after burning.Dike- The barrier or obstacle of a volcano.Sill- Slab of stone at the foot of the volcano.Flank- The side of a volcano.Lava- Matter flowing from a volcano that solidifies as it cools.Crater- Mouth of a volcano.Conduit- Channel or pipe conveying liquids such as lava.Summit- Highest point; apexThroat- Entrance of a volcano

Volcanism:Volcanism or volcanic activity is the term which includes both intrusion of magma

within the earth’s crust and the extrusion over the surface through the volcanoes.Volcanism is the process in which magma rises through Earth’s crust and issues forth at the surface as lava flows and/or pyroclastic materials and gases. Three major causes of volcanism are:-

∑ Gas release under decompression ∑ Thermal contraction from chilling on contact with water ∑ Ejection of entrained particles during steam eruptions

Volcanism can be explosive or non explosive in nature. Non Explosive type:-

• Mafic: refers to rocks and magma rich in iron and magnesium causes non explosive volcanism

• This type of lava that is very runny • As magma nears the surface there is little pressure, causing gasses escape easily.• Magma low in Silica have quiet eruptions

Explosive type:-• Felsic: means magma with high silica and feldspar content causes explosion• Felsic magma traps water and gas bubbles, which leads to lots of pressure• Silica acts like a cork• Explosive eruptions are caused by a buildup of high pressure• Convergent zones contain lots of water, therefore have explosive eruptions

Materials of volcanoes:Materials which are thrown out or erupted by volcanoes consist of solid, liquid and gases. All these are erupted at high temperature.

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A] Lava- Excessively hot, viscous and mobile liquid ejected by most of the volcanoes- it is the magma which has reached surface - it releases many gases and volatile components into atmosphere before or during eruption-Behaviour of lava depends on, composition, temperature, viscosity, gaseous content and the pressure with which it has been eruptedB] Pyroclasts- Solid Material that is thrown into the air during an explosion formed under pressure of rising lava- Volcanic blocks: Biggest fragments more than 32mm in dia. - Lapilli/Cinders: pebble size rocks or fragments in size of walnuts and pea- Volcanic tuff: Deposits of finest material/volcanic dust thrown by eruption - Volcanic Bombs: Solidified or semi solidified clots of lavaC] Gases- First to reach surface during eruption- acquire great heights and form dense clouds- Most dominant gas - steam- CO2, nitrogen, Hydrogen, CO, SO2

- Impart mobility to magma and supply pressure for upward movement of magmaTypes of volcanoes:

Volcanoes are found in three states - extinct, dormant and active. An extinct volcano will never erupt again which is inactive for considerable length of time. A dormant volcano has not erupted in 2000 years which may get erupted in future. An active volcano has erupted recently and is likely to erupt again. Kilauea Volcano, Hawaii. It is one of the world's most active volcano. Santa Isabel, Colombia. It is a extinct volcano. It last erupted in 1923. There are mainly four types of volcanoes based on volcanic cones:-1. Shield Volcanoes- largest volcanoes on Earth - Hawaiian shield volcanoes are the most famous examples- Broad, slightly dome-shaped (like an inverted shield)- Constructed by lateral flow of low-viscosity basaltic lava.- Have a low slope and cover large geographic areas- Eruptions at shield volcanoes are only explosive if water somehow gets into the vent otherwise they are characterized by low-explosivity

Examples: Kilauea and Mauna Loa, Fernandina, Karthala, Erta Ale, Tolbachik, Masaya.2. Cinder Cones- Small, steep-sided volcanoes made up of pyroclastic materials that resemble cinders are

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- Rarely higher than 400 m with slope angles up to 33 degrees, because they are made up of irregularly shaped particles- Large, bowl-shaped craters, and if they issue any lava flows at all, they usually break through the lower flanks rather than erupt from the crater - Often symmetrical, with a deep summit crater- Typically from a single eruption event

3. Strato volcanoes (also called composite volcanoes)- Large, cone-shaped volcanoes with steeper slopes- Made of alternating layers of lava, tephra, and debris- Another component of composite volcanoes is volcanic mud flows, or what geologists call lahars. A lahar may form when rain falls on unconsolidated pyroclastic materials and creates a mixture of particles and water that moves down slope

- Steep near their summits, with slope angles up to 30 degrees, but the slope decreases toward the base, where it may be no more than 5 degrees- Examples: Mount Fuji, Mount Rainier and Mount Vesuvius4. Lava domes- steep-sided, bulbous masses of viscous magma -small, isolated volcanic mountains, or they may rise into the craters of composite volcanoes-unstable and commonly collapse under their own weight, resulting in huge flows of debris- During both the 1980 and 2004 eruptions of Mount St. Helens in Washington, lava domes formed and were subsequently destroyed

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Types of Volcanic Eruptions:1. Central eruption- Also known as cone and crater type eruption- Cinder cone, Lava domes and Composite domes comes under this eruption [explain in brief as per question]- Further classified on the basis of nature of eruption:a. Hawaiian

These are eruptions of low viscosity basaltic lava. Gas discharge produces a fire fountain that shoots incandescent lava up to 1 km above the vent without much explosive noise. The lava, still molten when it returns to the surface flows away down slope as a lava flow. Hawaiian Eruptions are considered non-explosive eruptions. Very little pyroclastic material is produced. Produces shield volcanoes.b. Strombolian

These eruptions are characterized by thick, viscous lava in form of viscous paste or often in clots. These blasts produce in candescent bombs that fall near the vent, eventually building a small cone of tephra (cinder cone). Sometimes lava flows erupt from vents low on the flanks of the small cones. Strombolian eruptions are considered mildly explosive, and produce low elevation eruption columns and tephra fall deposits. c. Vulcanian

These eruptions are characterized by sustained explosions of solidified or highly viscous magma from the vent. Eruption columns can reach several km above the vent, and often collapse to produce pyroclastic flows. Widespread tephra falls are common. Vulcanian eruptions are considered very explosive.d. Pelean

These eruptions result from the collapse of an andesitic or rhyolitic lava dome, with or without a directed blast, to produce glowing avalanches or nuée ardentes, as a type of pyroclastic flow known as a block-and-ash flow. Pelean eruptions are considered violently explosive.e. Plinian

These eruptions result from a sustained ejection of a ndesitic to rhyolitic magma into eruption columns that may extend up to 45 km above the vent . Eruption columns produce wide-spread fall deposits with thickness decreasing away from the vent, and may exhibit eruption column collapse to produce pyroclastic flows. Plinian ash clouds can circle the Earth in a matter of days. Plinian eruptions are considered violently explosive.f. Phreatomagmatic

These eruptions are produced when magma comes in contact with shallow groundwater causing the groundwater to flash to steam and be ejected along with

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pre-existing fragments of the rock and tephra from the magma. Because the water expands so rapidly, these eruptions are violently explosive although the distribution of pyroclasts around the vent is much less than in a Plinian eruption.g. Phreatic(also called steam blast eruptions) - result when magma encounters shallow groundwater, flashing the groundwater to steam, which is explosively ejected along with pre-exiting fragments of rock. No new magma reaches the surface.2. Fissure eruption- Eruption with neither a cone nor a crater- Large volume of lava flow out from fissures and cracks continuously over a land- Spread in form of sheets burying everything in the way- Example: Deccan trap in Peninsular India3. Fumaroles- Cracks/ fissures from which hot gases come out regularly or intermittently- When there is no lava flow, only gases come out, and then it is fumaroles- Solfatars: Fumaroles discharging principally sulphurous vapours- example is Mid-Atlantic RidgeDistribution of volcanoes:About 62% of all active volcanoes in the world are located around the margins of the Pacific Ocean, although their distribution along this rim is irregular. The East Pacific Island Arc, for example, includes 45% of the world’s active volcanoes while the Central and South America segments contain only 17% of the volcanoes. About 14% of the volcanoes are located in the Indonesian Islands arc while, of the remaining 24%, 3% are located in the mid-Pacific Ocean, 1% in mid-Indian Ocean islands, 13% on mid-Atlantic Ocean islands, and the last 7% scattered through the Mediterranean Sea and Central Asia (Turkey, Iraq, etc.) and the inner part of continents, for example, the African Rift. It is possible to divide the volcanoes of the world into seven regions as follows: (1) volcanoes of the Pacific Ocean island arcs and Alaska continental rim,(2) volcanoes of the East Pacific continental rim, (3) volcanoes of alpine-Indonesian mountain belt, (4) volcanoes of East African–Arabian belt, (5) volcanoes of the rifts and mountains of Eurasia, (6) volcanoes of the West Indies island arc, and (7) volcanoes of the ocean floor.

9. SIESMOLOGY

Seismology is the study of the generation, propagation and measurement of seismic waves through earth and the sources that generate them. The word seismology originated from Greek words, ‘seismos’ meaning earthquake and ‘logos’ meaning science. The study of seismic wave propagation through earth provides the maximum input to the understanding of internal structure of earth.Continental drift theory

German scientist Alfred Wegener, in 1915, proposed the hypothesis that the continents had once formed a single landmass before breaking apart and drifting to their present locations. His observations were based on the similarity of coastlines and geology between south America, Africa and Indian peninsula, Australia and Antarctica. He proposed that a large continent termed Pangae existed in earth around 200 million years ago and was surrounded by an ocean called Panthalassa. It was postulated that this super continent broke into several pieces that formed the present continents. These pieces have subsequently drifted into their current position. Although, he presented much evidence forcontinental drift, he was unable to provide a convincing explanation for the physical processes which might have caused this drift. He suggested that the continents had been

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pulled apart by the centrifugal pseudo force of the Earth's rotation or by a small component of astronomical precession. But the calculations showed that these forces were not sufficient cause continental drift.Plate tectonics

The theory of plate tectonics, presented in early 1960s, explains that the lithosphere is broken into seven large (and several smaller) segments called plates. The upper most part of the earth is considered to be divided into two layers with different deformation properties. The upper rigid layer, called the lithosphere, is about 100 km thick below the continents, and about 50 km under the oceans, and consists of Crust and rigid upper-mantle rocks. The lower layer, called the asthenosphere, extends down to about 700 km depth. The rigid lithospheric shell isbroken into several irregularly shaped major plates and a large number of minor or secondary plates. The lithospheric plates are not stationary, on the contrary, they float in a complex pattern, with a velocity of some 2-10 cm/year on the soft rocks of the underlying asthenosphere like rafts on a lake. This theory requires a source that can generate tremendous force is acting on the plates. The widely accepted explanation is based on the force offered by convection currents created by thermo-mechanical behavior of the earth’s subsurface. The variation of mantle density with temperature produces an unstable equilibrium. The colder and denser upper layer sinks under the action of gravity to the warmer bottom layer which is less dense. The lesser dense material rises upwards and the colder material as it sinks gets heated up and becomes less dense These convection currents create shear stresses at the bottom of the plates which drags them along the surface of earth. Elastic Rebound theory

As the plate try to move relative to each other, strain energy gets built up along the boundaries. When the stress buildup reaches the ultimate strength of rock, rock fractures and releases the accumulated strain energy, Figure 1.13. The nature of failure dictates the effect of the fracture. If the material is very ductile and weak, hardly any strain energy could be stored in the plates due to their movement. But if the material is strong and brittle, the stress built up and subsequent sudden rupture releases the energy stored in the form of stress waves and heat. The propagation of these elastic stress waves causes the vibratory motion associated with earthquakes. The region on the fault, where rupture initiates is known as the focus or hypocenter of an earthquake. Epicenter is the location on the earth surface vertically above the focus. Distance from epicenter to any place of interest is called the epicentral distance. The depth of the focus from the epicenter is the focal depth. Earthquakes are sometime classified into shallow focus, intermediate focus and deep focus earthquakes based on its focal depth. Most of the damaging earthquakes are shallow focus earthquakes.Earthquake is the vibration of earth’s surface caused by waves coming from a source of disturbance inside the earth. Most earthquakes of engineering significance are of tectonic origin and is caused by slip along geological faults.The typical characteristics of earthquake depends on1. Stress drop during the slip2. Total fault displacement3. Size of slipped area4. Roughness of the slipping process5. Fault shape ( Normal fault, Reverse fault, Strike slip fault)6. Proximity of the slipped area to the ground surface7. Soil condition

As the waves radiate from the fault, they undergo geometric spreading and

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attenuation due to loss of energy in the rocks. Since the interior of the earth consists of heterogeneous formations, the waves undergo multiple reflections, retraction, dispersion and attenuation as they travel. The seismic waves arriving at a site on the surface of the earth are a result of complex superposition giving rise to irregular motion Earthquake vibrations originate from the point of initiation of rupture and propagates in all directions. These vibrations travel through the rocks in the form of elastic waves. Mainly there are three types of waves associated with propagation of an elastic stress wave generated by an earthquake. These are primary (P) waves, secondary (S) waves and surface waves. In addition, there are sub varieties among them. The important characteristics of these three kinds of waves are as follows:Primary (P) WavesThese are known as primary waves, push-pull waves, longitudinal waves, compressional waves, etc. These waves propagate by longitudinal or compressive action, which mean that the ground is alternately compressed and dilated in the direction of propagation. P waves are the fastest among the seismic waves and travel as fast as 8 to 13 km per second. Therefore, when an earthquake occurs, these are the first waves to reach any seismic station and hence the first to be recorded. The P waves resemble sound waves because these too are compressional or longitudinal waves in nature. Hence, the particles vibrate to and fro in the direction of propagation (i.e. longitudinal particle motion). These waves are capable of traveling through solids, liquids and gases.Secondary (S) Waves

These are also called shear waves, secondary waves, transverse waves, etc. Compared to P waves, these are relatively slow. These are transverse or shear waves, which mean that the ground is displaced perpendicularly to the direction of propagation,. In nature, these are like light waves, i.e., the waves move perpendicular to the direction of propagation. Hence, transverse particle motion is characteristic of these waves. These waves are capable of traveling only through solids. If the particle motion is parallel to prominent planes in the medium they are called SH waves. They travel at the rate of 5 to 7 km per second. For this reason these waves are always recorded after P waves in a seismic station.Surface Waves

When the vibratory wave energy is propogating near the surface of the earth rather than deep in the interior, two other types of waves known a Rayleigh and Love waves can be identified. These are called surface waves because their journey is confined to the surface layers of the earth only. Surface waves travel through the earth crust and does not propagate into the interior of earth unlike P or S waves. Surface waves are the slowest among the seismic waves. Therefore, these are the last to be recorded in the seismic station at the time of occurrence of the earthquake. They travel at the rate of 4 to 5 km per second. Complex and elliptical particle motion is characteristic of these waves. These waves are capable of travelling through solids and liquids. They are complex in nature and are said to be of twokinds, namely, Raleigh waves and Love waves. The motion of plates results in stress buildup along plate boundaries as well as in interior domain of the plate. Depending on the state of buildup of stress and amount of resistance offered by the fault strata, rupture is initiated as stress exceeds the capacity of the strata. Generally, the rupture causing earthquakes initiates from a point, termed as hypocenter or focus, which subsequently spreads over to a large area. Depending on the characteristics of strata where rupture occurs, the shape of the ruptured area could be highly irregular and the amount of interface slip along the ruptured surface could also vary.

The place of origin of the earthquake in the interior of the earth is known as focus or

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origin or centre or hypocenter. The place on the earth's surface, which lies exactly above the centre of the earthquake, is known as the 'epicenter'. For obvious reasons, the destruction caused by the earthquake at this place will always be maximum and with an increasing distance from this point, the intensity of destruction also decreases. The point on earth's surface diametrically opposite to the epicenter is called the anti-center. An imaginary line which joins the points at which the earthquake waves have arrived at the earth's surface at the same time is called a 'co-seismal'. In homogeneous grounds with plain surfaces, the iso-seismals and coseismals coincide. Of course, in many cases due to surface and subsurface irregularities, such coincidence may not occur.Recording Earthquakes

The vibratory motion produced during an earthquake could be measured in terms of displacement, velocity or acceleration. A seismologist is interested in even small amplitude ground motions (in terms of displacement) that provides insight into the wave propagation characteristics and enables him to estimate the associated earthquake parameters. As accelerations are the causative phenomena for forces that damage structures (Force = mass x acceleration), engineers are more concerned with the earthquake causing structural damage, hence are interested in acceleration measurement. The instruments measure the ground displacements and are called seismographs. The record obtained from a seismograph is called a seismogram.

The seismograph has three components – the sensor, the recorder and the timer. The principle on which it works is simple and is explicitly reflected in the early seismograph –a pen attached at the tip of an oscillating simple pendulum (a mass hung by a string from a support) marks on a chart paper that is held on a drum rotating at a constant speed. A magnet around the string provides required damping to control the amplitude of oscillations. The pendulum mass, string, magnet and support together constitute the sensor; the drum, pen and chart paper constitutes the recorder; and the motor that rotates the drum at constant speed forms the timer. By varying the characteristics of equipment one could record displacement, velocity or acceleration during an earthquake. The devises that measure the ground accelerations are called accelerometer. The accelerometers register the accelerations of the soil and the record obtained is called an accelerogram. Size of Earthquakes

The size of earthquake could be related to the damage caused or parameters like magnitude. These two useful definitions of the size of earthquakes are sometimes confused.Intensity of Earthquakes

The intensity of an earthquake refers to the degree of destruction caused by it. In other words, intensity of an earthquake is a measure of severity of the shaking of ground and its attendant damage. This, of course, is empirical to some extent because the extent of destruction or damage that takes place to a construction at a given place depends on many factors.

10. EARTHQUAKES: SECONDARY EFFECTS

The energy released from an earthquake can be up to 10,000 times more powerful than the first atomic bomb. Its side-effects can be:

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Ground shaking

Shaking of the ground caused by the passage of seismic waves, especially surface waves near the epicentre of the earthquake are responsible for the most damage during an earthquake. The intensity of ground shaking depends on:

∑ conditions of the local geology influence. solid bedrock is far less subject to intense shaking than loose sediment

∑ duration and intensity of the earthquake are subject generally to the size of the earthquake

∑ distance: ss the distance from the epicentre drops off so the intensity of the shaking decreases. This depends on the type of material underlying the area. There are however some exceptions. The 1985 Earthquake in Mexico city (magnitude 8.1) had its epicentre 350 Kms away to the south on the coast. Damage to city was extensive as Mexico city is built on a former lake made up of soft unconsolidated sediment (see: Liquefaction further down).

Faulting and Ground Rupture

When an earthquake event occurs, ground rupture is only where the fault zone moves. Those constructions built adjacent to the fault will survive while structures built across these zones will collapse.

Landslides and ground subsidence

Avalanches, landslides, slumps and rock slides are triggered by ground shaking. These landslides are often more destructive than the earthquakes. A residential area in Alaska (Turnagain Heights) was destroyed by a shock induced landslide as well as are in downtown Anchorage.

Damage to man-made structures

Damage to man-made structures, such as roads, bridges, dams and buildings from ground motion depends on the type of construction:

∑ concrete and masonry structures are brittle and thus more susceptible to damage and collapse;

∑ damage to wood and steel structures is far less because of its flexibility.

Fires

Fires, often associated with broken electrical and gas lines, is one of the common side effects of earthquakes. Gas is set free as gas lines are broken and a spark will start bringing "inferno". To complicate things water lines are broken and so there is no water to extinguish the fire. The San Francisco earthquake of 1906 caused 90% of damage by fire.

Spill of hazardous chemicals

Christchurch Earthquake (New Zealand, 2010). Kocaeli chemicals spill (Turkey, 1999

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Liquefaction of water-laden sediments

Groundwater, sand and soil combine during seismic shaking to form liquefaction during a moderate to powerful earthquake. A quicksand like soil is the result of this process. When liquefaction takes place under buildings the foundations sink and the building collapse. After the earthquake has passed, the soil firms again and the water settles deeper in the ground. Areas with sandy soil and groundwater close to the surface are far more at risk of liquefaction.

Flooding

Flooding can come from many sources such as broken water main pipes, dams that fail due to the earthquake and earthquake-generated tsunamis. When an earthquake breaks a dam or levee along a river, the water from the river or the reservoir floods the area, damaging buildings and maybe sweeping away or drowning people. Small tsunamis, called seiches occur on lakes shaken by earthquakes and are usually just a few feet high. These small tsunamis are capable of destroying houses and uprooting trees. Also, earthquakes can alter the course of a river and can even cause it to flow in the opposite direction for a short time (this happened to the Mississippi River in the late 1800's).

A seiche is the effect of the sloshing of water back and forth. A seiche can be caused by an earthquake and/or a tsunami. The earthquake from Alaska on March 28th, 1964 caused seismic waves that were so powerful that bodies of water oscillated in many places across North America. Hundreds of surface water gauging stations recorded seiches although rarely recorded before this earthquake.

Tsunamis

For sure, one of the most dangerous effects of an earthquake is a Tsunami. Tsunamis are giant waves that can cause floods and in some cases may reach up to 100 feet in height. These deadly waves strike a great distance from the epicentre. Tsunamis often result from sub-sea faulting of ocean floor sending seismic shocks through the water and creating large waves of low amplitude but of long period, moving at 500-700 mph.

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