A.D.M. COLLEGE FOR WOMEN (AUTONOMOUS), NAGAPATTINAM
DEPARTMENT OF GEOLOGY
PHYSICAL GEOLOGY
II B.Sc. GEOLOGY
UNIT-1
PHYSICAL GEOLOGY:
Physical geology is the branch of geology that deals with the processes that change the physical landscape of the planet.
Weathering:
The rocks break and undergo decay under the influence of the atmospheric agencies like wind, sun, frost, water and organisms and produce soil. This phenomenon is called weathering.
Wind, sun, frost, water and organisms
Soil Rock
decay breaks
Weathering process:
It includes two processes:
• Disintegration
• Decomposition
Weathering:
• Erosion
• Transportation
• Deposition
Erosion:
Erosion is a process which includes the destruction of existing rocks and removal for the product from the site of destruction.
Denudation:
The combined process of weathering and erosion is known as denudation.
Transportation:
The process through which the eroded materials are carried from one place to another is known as transportation.
Deposition:
The process through which the eroded particles get deposited in a place where it meets an obstacle or a basin is known as deposition.
Types of weathering:
There are three types of weathering. They are as follows:
a) Physical weathering b) Chemical weathering c) Biological weathering a)Physical weathering:
• Physical weathering is also known as mechanical weathering. • Physical weathering occurs when physical forces break a rock into smaller and smaller pieces without changing the rock mineral composition.
• These forces are wind, water, waves and gravity.
• This type of weathering happens especially in places where there is little soil and few plants grow such as in mountain regions and hot deserts.
• It can occur due to temperature, pressure, frost etc.
i)Frost wedging:
When water freezes, it expands about nine percent of volume. In nature water enters into cracks of rocks. Upon freezing expands and exerts great pressure on the walls of cracks. As a result the rock breaks into pieces. This process is called frost wedging.
ii) Exfoliation:
• It is mainly a physical weathering process in which large sheets of rock peel of from an outcrop. • In exfoliation reduction in pressure due to removal of overlying rock plays an important part.
• As each slab breaks off, it releases weight from the underlying mass.
• As a result its outer layers expand and separate from the rock mass.
iii)Thermal expansion:
• It occurs due to the repeated heating and cooling of rocks.
• It mostly occurs in desert environments.
• In the rocks heating causes expansion and cooling causes contraction. b)Chemical weathering:
• Chemical weathering is a process in which rocks are broken down by chemical decay of minerals.
• Water is the most important agent of chemical weathering.
• Two other important agents of chemical weathering are carbon dioxide and oxygen.
i)Water:
Although water in pure form is inactive, it becomes a powerful chemical agent when a small amount of oxygen and carbon dioxide are dissolved in it. Rain water usually contains these gases. The main reactions involved in the chemical weathering are oxidation, hydration, carbonation and solution.
Oxidation: The oxygen present in the water in dissolved state oxidizes some minerals. When iron in rock reacts with oxygen it forms iron oxide, which weakens the rock. Limonite and hematite are very common products of oxidation.
Hydration: In hydration water molecules combine chemically with minerals to produce new compounds. The formation of gypsum (CaSO2.2H2O) from anhydrite (CaSO4) is a good example of hydration.
Carbonation: Carbon dioxide dissolves in water to form carbonic acid (H2O3). Carbonic acid is an effective weathering agent. Granite under the influence of carbonic acid it weathers into clay.
ii) Organisms:
Many dead organisms produce organic acids as they decay. These acids increase the solvent power of water. For example the solubility of silica alumina and iron is much greater in the presence of organic acid. c) Biological weathering:
• Biological weathering is caused by plants and animals. • Plants and animals release acid forming chemicals that cause weathering and also contribute to the breaking down of rocks and landforms.
Factors influencing rate of weathering
• Rock structures- chemical/ mineral composition
• Topography
• Climate
• Vegetation
• Time
Products of weathering:
• The products of weathering and erosion are the unconsolidated materials that we find around us on slopes, beneath glaciers, in stream valleys, on beaches, and in deserts.
• The nature of these materials ie their composition, size, degree of sorting, and degree of rounding is determined by the type of rock that is being weathered, the nature of the weathering, the erosion and transportation processes, and the climate.
Products Of Weathering:
• Regolith
• Sediments
• Dissolved ions
Soil:
Any solid unconsolidated material lying on top of bedrock is called regolith. A portion of regolith which supports the growth of plants is called soil.
A-Horizon: Uppermost layer of the soil profile. It is also known as surface soil. It contains organic matter and micro-organisms.
B-Horizon: Also known as subsoil and zone of accumulation. Materials leached in A- horizon are deposited here.
C-Horizon: The lower horizon. It consists of partly altered parent rock material.
WEATHER AND CLIMATE
Sl.No. WEATHER CLIMATE 1 The day to day information of Climate is the statistical information of atmospheric changes of a particular the average weather condition of a area at a specific time is called specific region for more than 30years. weather. 2 The weather of a place includes the The climate of a country or zone short-term atmospheric condition. includes the long term average Also, these atmospheric conditions can atmospheric conditions. Thus, the change within a short period like climate is average weather information minutes, hours, days etc.. observed over decades. 3 The atmospheric elements of weather When the atmospheric elements of are air pressure, humidity, wind, weather are observed over the decades, temperature, rain, cloudiness, storms, those become the affecting conditions of snow, precipitation etc. These climate. These conditions can include conditions can affect the weather of the temperature, humidity, wind etc. place within a short time. 4 The weather of a particular location The climate of a country significantly can impact the day to day human life impacts industries, agriculture, the like occupation, transportation, livelihood of the inhabitants of that communication, agriculture etc. geographical locale. 5 Weather conditions change very Climate conditions change over a long frequently. period. 6 The meteorological department of a Institutes of climate studies observe and place observes the changes in weather predict the changes in climate. This conditions. The study of weather study is called climatology. forcasting is known as meteorology.
Economic importance of weathering:
• Produces unconsolidated material from which soil is formed.
• Provides plant nutrients.
• Results in the formation of secondary minerals, the most important group being the clay minerals.
• It weakens the rocks making them easier for people to exploit.
• Weathering of rocks and deposits helps in concentration of some valuable ores of manganese, aluminum, iron copper etc. Which have a great significance in the economy of the country.
Atmosphere:
The atmosphere is the blanket of air that surrounds the earth.
Composition of air:
• Nitrogen -78
• Oxygen -21
• Other gases -1
• Greenhouse gases –Carbon dioxide, methane, water vapor etc.
Earth's atmosphere is divided into five main layers: the exosphere, the thermosphere, the mesosphere, the stratosphere and the troposphere. There is no distinct boundary between the atmosphere and space, but an imaginary line about 62 miles (100 kilometers) from the surface, called the Karman line, is usually where scientists say atmosphere meets outer space.
Troposphere:
• It is the layer closest to the Earths surface.
• Its thickness is about 12km.
• Temperature decreases with altitude.
• Weather changes takes place.
• Vertical air currents.
• Contains 75% of air.
• Composition- Oxygen and nitrogen.
Stratosphere:
• Second layer of atmosphere.
• Extends upto 50km.
• Horizontal air currents.
• Temperature increases with altitude.
• Contains the ozone layer in the upper part. • Jet planes travels here.
• Contains 24% of air.
• Uppermost part of stratosphere is known as stratopause.
Mesosphere:
• Third layer of the atmosphere.
• Extends upto 90km.
• Temperature decreases with altitude.
• Coldest layer.
• Meteors burn here.
• Uppermost part of Mesosphere is known as mesopause.
Thermosphere:
• Fourth layer of the atmosphere.
• Extends upto 800km.
• Hottest layer.
• Temperature increases with altitude. Uppermost part of the thermosphere is called thermopause.
Exosphere:
• Outermost layer of the Earths atmosphere. • It is composed of hydrogen, helium and several heavier molecules including nitrogen, oxygen and carbon dioxide.
Wind
The air current in motion is called wind. Wind is an important agent of erosion, transportation and deposition. Its work is particularly seen in arid regions.
AEOLIAN PROCESSES AND LANDFORMS:
Wind erosion:
Wind does erosion in three ways:
a)Deflation
b)Abrasion
c)Attrition
a)Deflation:
• Lifting and removal of loose materials is known as Deflation.
• By this process land surface is gradually lowered.
• In many desert paces deflation produces hollows or basins with their bottom at water table.
• Such basins containing some water are called oasis. b)Abrasion:
• During dust storms the wind carries minute grains of sand in suspension.
• They dash and colloid with the exposed rock masses and cause erosion. • This process in which sand grains are used as tools for eroding rocks is known as abrasion or sand blasting.
C)Attrition:
• The particles which travel in wind colloid against one another.
• These mutual collision leads to the further break down and the process is called attrition.
Erosional landforms:
a) Ventifacts:
Formed by abrasion effect.2.Exhibit one or more polished and faceted surfaces. They are relatively rare.
b)Yardang:
Yardang, large area of soft, poorly consolidated rock and bedrock surfaces that have been extensively grooved, fluted, and pitted by wind erosion. They are formed due to Abrasion and deflation process of Wind. It is elongated in the direction of prevailing wind.
c)Pedestal rock or mushroom rock:
A rock having a broad upper and narrow base resembling an mushroom shape is known as pedestal rock. It is formed due to the abrasive work of wind.
d)Desert pavements:
The left behind closely packed, interlocking, angular or rounded rock fragments of pebble and cobble is known as log deposits. It is formed due to deflation process.
Transportation:
Transportation by wind occurs in three ways:
a)Saltation
b)Suspension
c)Rolling or traction a) Saltation: Particles transported through a series of bounces is known as Saltation. b) Suspension: Particles are lifted high into atmosphere and carried to a great distance. This process is known as Suspension. c) Rolling: The movement of particles on the ground is known as rolling. Rolling is also known as traction.
Deposition:
• Reduction in velocity
• Any obstruction to wind
• Increased load
Depositional landforms: a) Sand ripples:
Miniature dunes within a dune is known as sand ripples. Its height is less than 2inches. May form from cross winds and appear to be travelling in different direction than the large dune.
b)Loess:
It is a depositional landform formed due to the accumulation of wind blown silt. These deposits are non-stratified with grayish yellow color. Loess is composed of many minerals including quartz, feldspar, hornblende and calcite. These deposits are very fertile. c)Sand dunes:
Accumulation of sand deposited by wind is known as sand dunes. Leeward side of the dune is steeper and windward side is gentler. Sand dunes slowly migrate in the direction of wind movement.
Types of sand dunes:
There are five types of sand dunes. They are as follows:
a)Transverse dunes
b)Barchans dunes
c)Longitudinal/seif dunes
d)star dunes
e)Parabolic dunes
a) Transverse dunes: Transverse dunes have their longer axis right angles to the direction of wind. They are formed in the areas with strong wind where more sand is available. b) Barchans dunes: Crescent shaped dunes the convex side of which faces the wind direction. The horns and wings of the crescent points the wind direction. Barchans are formed where wind is unidirectional. They occur in groups in areas of greatest sand supply. The height of large dunes does not exceed 30meters and their point to point length is 300meters.
c) Longitudinal dunes: The dunes which are elongated in wind direction is called longitudinal dunes. These dunes generally develop in strong winds in areas where small amount of sand is available. They may reach a height of 100meters and may extend for about 90kilometers.
d) Star dunes: Star dunes are sand dunes that form in a sandy desert when the direction of the wind changes a lot. These dunes have three or more “arms”, usually irregularly shaped. The dunes may grow to a considerable height and are generally taller than other types of sand dune.
e) Parabolic wind: Parabolic dunes require strong and unidirectional winds. They indicate the presence of a stabilizing agent, commonly vegetation cover.
Arid cycle of erosion: 1) Initial stage:
• The initial stage of arid cycle of erosion of mountain-grit deserts is characterized by extremely dry climate (mean annual rainfall less than 25 cm), upliftment of deserts by folding or faulting, development of intermontane basins, initiation of inland and centripetal drainage etc.
• Evaporation is very active. Playa is formed due to accumulation of some water in the center of the basins.
2) Youth Stage:
• Erosion and deposition both go hand in hand and thus the initial reliefs are gradually reduced because of erosion of the mountains and filling of the basins .
• The lower segments of hill slopes are more vigorously dissected by rill and gully erosion caused by occasional rainstorms.
3) Maturity Stage: • Relief decreases rapidly because of progressive erosion of mountain divides and filling of enclosed basins. • The progressive recession of water divides increases the size of enclosed basins. • The level of these basins also rises because of gradual sedimentation. • Bajadas are further enriched, widened, and extended upslope. • Extensive rock-cut pediments are formed between the receding mountain fronts and bajada zone. • Deflation of sands by wind becomes more active. • This process causes bare surfaces or desert pavements.
4) Old stage:
• All the highlands are reduced to almost plain surface of very low height.
• Numerous residual hills project above the general flat surface.
• Deflation of sands by wind is most active.
• Several pediments are coalesced and form extensive pediplains.
Characteristics of desert
• Aridity -Common in all deserts. • Extremes of temperature -Fluctuations in day and night temperatures and also in seasons. • Humidity-Low humidity during the day and comparatively high in night. • Precipitation • Drought-It is temporary or permanent guest of deserts. The duration of drought is long in arid zone and decreases towards the margin. • High wind velocity • Absence of water vapor in air • Soils loose, sandy devoid of organic carbon, nitrogen, moisture etc. • Vegetation is scarce • Scarcity of water
UNIT-2
RUNNING WATER
The geological work of running water erodes the valleys transport the materials thus eroded and deposit the same in lower reaches at favorable sites.
Erosion:
Running water causes erosion in four ways. They are
• Chemical action
• Hydraulic action
• Abrasion
• Attrition
Chemical action:
It involves the solvent and chemical action of country rock. The chemical decay works along the cracks and joints and thus helps in breaking bedrocks.
Hydraulic action:
The swiftly flowing water hammers the uneven faces of jointed rocks exposed along its channel and remove the jointed blocks. This process is called hydraulic action. At the bottom of the waterfalls, the channels are eroded at an enormously rapid rate by the hydraulic action.
Abrasion:
The flowing water uses the pebbles, gravels and sands as a tool for scratching and grinding the sides and floor of the valley.
Attrition:
It is the breaking of transported materials themselves due to mutual collision. The attrition causes the rock fragments to become more rounded and smaller in size.
Erosional landforms:
• Potholes
• Waterfalls
• Gorges
• Meanders
• Oxbow lakes
• Entrenched meanders
Potholes:
Potholes are circular and deep holes cut into solid rocks by sand grains and a pebble, swirling in fast eddies. They are commonly found on the channel floor.
Waterfalls:
Falling of stream water from height is called waterfalls. Waterfalls occur at places where the stream profile makes a vertical drop. Such a situation is usually found where gently inclined, erosion resistant beds overlie the nonresistant beds. The softer rock is eroded fast while the harder one offers resistance and forms a ledge at a height, from which the steam’s water falls down deep into the gorge. When the water falls over the ledge, it erodes the less resistant beds of the cliff. Due to this undercutting a portion of the upper resistant bed breaks off and the waterfall retains its vertical cliff while it gradually moves upstream.
Gorges:
Narrow and deep river valleys which develop in hard rocks are called gorges.
Meanders:
The symmetrical S-shaped loops found in the course of a river, are called “Meanders”. Meanders develop in mature rivers. Meanders grow due to deposition of sediment along the slip off side and erosion at the undercut side. Meanders continually change their position. They move both downstream and to the side.
Oxbow lakes:
• Meanders grow by eroding its outer bank and depositing sediments in the inner bank.
• During this process the sharpness of the river bend increases progressively and the neck of the meander becomes narrow and narrow.
• Finally the stage comes when the river cuts through the neck and starts flowing straight leaving behind its roundabout course.
• Such left out old meanders which remain filled with stagnant water are called oxbow lakes.
Entrenched meanders:
• On many occasions, the land gets uplifted.
• The uplifting of a mature stream would cause it to give up lateral erosion and revert to down cutting. • Rivers of this type are said to be rejuvenated.
• When a meandering river is rejuvenated, it starts down cutting again.
• As a result the meandering channel is deepened and the old meanders get entrenched into the bedrock.
Such meanders are called entrenched meanders.
Transportation
• The amount of solid material transported by a stream is called load.
• The streams transport in three ways:
➢ In solution(dissolved load)
➢ In suspension(suspended load)
➢ Along the bottom(bed load)
Dissolved load: The dissolved load is bought to the stream by groundwater. Some amount of it is also acquired from soluble rocks which occur along the streams course.
Suspended load: Suspended load forms the major portion of the load carried by the steam. Usually only smaller substance such as clay and silt are carried through suspension but during floods much larger particles are carried this way.
Bed load: The forward force of moving water acts more directly on the larger grains on the bottom pushing, rolling and sliding them along. The particles moved this way constitutes the bed load of a stream.
Saltation: The process of intermittent jumping is called saltation. Small pebbles and stones are bounced along the river bed. Rolling: Large boulders and rocks are rolled along the river bed.
Deposition:
• The loose rock materials transport by a stream downstream are deposited where the velocity of flowing water is reduced.
• The sorting of materials takes place automatically as the large and heavier particles settle quickly while the small and lighter ones continue their journey further ahead.
• The materials which a stream deposit as sediment is called alluvium or alluvial deposits.
Depositional landforms:
• Alluvial fans
• Flood plains
• Natural levees
• Point bars
• Deltas
Alluvial fans:
• The alluvial materials which flows down from mountains, accumulate at foot hills where the stream enters a plain.
• The deposition occurs due to abrupt change in the gradient in river valley. Such deposits spread out in the shape of fans and are called “alluvial fans”.
• Usually the coarse material is dropped near the base of the slope while finer material is carried further out of the plain. • Alluvial fans from many adjacent streams along a mountain may merge to form a long wedge of sediment called “alluvial aprons”.
Flood plains
• During floods a river overflows its bank and sub-merges the adjacent low lying areas where deposition of alluvial material takes place.
• A wide belt of alluvial plain formed in this way on either side of a stream is called “flood plains”.
Natural levees
• Natural levees are low ridges which are formed on the both sides of the river channel by the accumulations of sediments.
• They tend to confine the flow of river water into its channels between flood stages.
• The natural levees occur in rivers which have broad flood plains.
• During flood the river overflows its banks and its velocity decreases rapidly. • As a result most of the coarse sediment is deposited along the area bordering the river channel and finer sediments are deposited more widely over the flood plain.
• In this way successive floods build up ridges on both sides of the river channel, which are called natural levees.
Point bars
• In meandering rivers, sediment deposits occur as point bars.
• The point bars are the crescent shaped deposits which occur at the inner bends of a river channel.
Deltas
• Deltas are deposits built at the mouth of the river.
• The deltas are usually triangular in shape with their apex pointed upstream.
• When a stream enters an ocean or lake, the currents of the ocean water dissipates quickly.
• This results in deposition of series of sedimentary layers which makes up the delta.
Drainage system
• A land area surrounded by divides which contributes water to a river is called Drainage basin.
• Although all drainage networks branch in the same way the shape of their pattern varies greatly from one kind of terrain to the other, depending upon the rock type or structure.
• The chief drainage patterns are
➢ Dendritic ➢ Trellis
➢ Rectangular
➢ Radial
➢ Parallel
Dendritic pattern
• In dendritic pattern the stream show a branching tree like arrangement.
• This pattern develops in terrains covered with uniform rock types, such as horizontal sedimentary rocks or massive igneous or metamorphic rocks.
Trellis pattern
• A trellis pattern is one in which major streams are parallel and short tributaries join the main streams at nearly right angles.
• This type of drainage pattern develops in regions containing folded or tilted strata.
• Here the main stream develops in the strike valleys cut into the soft rocks, while tributaries flow down the resistant ridges.
Rectangular pattern • Differentiated weathering of faults and joint systems in bedrocks localizes the stream flow producing a more ordered rectangular drainage.
• In a rectangular drainage pattern angular deflection of stream courses are apparent.
Radial pattern
• In a radial drainage pattern streams flow outward in different directions from a central high point.
• This pattern commonly develops on an elevated structure such as volcano or dome.
Parallel pattern
• This type of drainage pattern develops in a terrain containing tilted rock beds and parallel faults.
• The major stream occupies the fault while tributaries which are parallel, meet the stream approximately at the same angle.
Stages of valley development:
The development of stream valleys takes place in a orderly fashion. A valley process through three stages during its evolution. The three stages are
➢ Youth stage
➢ Mature stage
➢ Old stage
Youth stage:
A stream is said to be in the youth stage when it cuts its valley downward to establish a graded condition with its base level.
a) Position: The youth stage is commonly found in mountainous regions from where a stream starts its journey.
b) Erosion: Down cutting is dominant
c) Valley: Narrow V-shaped valley.
d) Longitudinal profile: Longitudinal profile is ungraded. The gradient is steep and waterfalls and rapids are common. e) Valley floor: The stream occupies most of the width of the valley floor as a result there is little or no flood plain.
f) Stream pattern: The stream course is angular and without meanders. Tributaries are short and few.
Mature stage:
A stream is said to be in the youth stage when downward erosion diminishes and lateral erosion dominates.
a) Position: Mature stage is found in the plains lying adjacent to the mountain region.
b) Erosion: Downward cutting is slight and side cutting becomes dominant.
c) Valley: Broad and trough shaped.
d) Longitudinal profile: Waterfalls and rapids are absent. Valley bottom is graded so that the longitudinal profile exhibits a relatively smooth curve. The gradient is moderate.
e) Valley floor: The stream swings in meanders. The flood plains are narrow and sandbars are present.
f) Stream pattern: The stream moves in meanders. The tributaries are many.
Old stage:
In old stage, the flood plains of a stream becomes several times wider than its meander belt.
a) Position: The old stage is found near the mouth of streams.
b) Erosion: In the old stage, the stream ceases to enlarge the flood plain. The main work of the stream is to network, the unconsolidated sediment of the flood plain.
c) Valley: Valleys become wide and open with low boundaries which may be indistinct.
d) Longitudinal profile: The gradient becomes very low. The stream approaches base level and it aggrades strongly.
e) Valley floor: Oxbow lakes are common. Natural levees are also present. They are accompanied by back swamps and yazoo tributaries. The meander belt is narrower than the valley floor.
f) Stream pattern: The stream pattern is meandering with oxbow lakes. The tributaries are few and large.
STREAM REJUENATION
Rejuvenation:
In geomorphology a river is said to be rejuvenated when it is eroding the landscape in response to a lowering of its base level. The process is often a result of a sudden fall in sea level or the rise of land.
Causes of Rejuvenation
• A river rejuvenates when there is an increase in gravitational potential energy.
• It causes the river to erode its bed vertically to achieve equilibrium with the slope of the landscape.
• The river's natural long profile is a concave curve; steeper at the start and gentler towards the end.
• When this curve is disturbed by a movement in sea level, the river erodes its way back to a course that resembles a concave curve.
Types of rejuvenation include:
• Dynamic Rejuvenation: A result of isostatic change, when land rises due to faulting and the river must begin active downward erosion.
• Eustatic Rejuvenation: Result of global sea level change because of ice caps melting or forming. When sea levels fall, eustatic rejuvenation affects the mouth of the river, and the river erodes it's way back towards its source, creating waterfalls, rapids and incised meanders.
• Static Rejuvenation: Caused by a decrease in load or an increase in run-off, usually in the upper course of the river after glaciers have melted. Leads to valleys getting deeper.
Unit III
UNDERGROUNDWATER
Groundwater derived from rainfall and infiltration within the normal hydrological cycle. This kind of water is called meteoric water. The name implies recent contact with the atmosphere. Groundwater encountered at great depths in sedimentary rocks as a result of water having been trapped in marine sediments at the time of their deposition. This type of groundwater is referred to as connate waters. These waters are normally saline. It is accepted that connate water is derived mainly or entirely from entrapped sea water as original sea water has moved from its original place. Some trapped water may be brackish. Fossil water if fresh may be originated from the fact of climate change phenomenon, some areas used to have wet weather and the aquifers of that area were recharged and then the weather of that area becomes dry.
WATER TABLE The subsoil horizon below the surface is called as the zone of aeration or vadose zone. Below this zone there is water saturated media is called as the ground water. The upper most surface of the zone of saturation is termed as the water table. Water table forms the boundary between the zone of aeration and zone of saturation.
ZONE OF SATURATION In Zone of saturation all interstices are filled with water under hydrostatic pressure. In the zone of saturation, groundwater fills all of the interstices; hence the porosity provides a direct measure of the water contained per unit volume. A portion of the water can be removed from subsurface strata by drainage or by pumping of a well. However, molecular and surface tension forces hold remainder of the water in place.
What is spring? A spring is a place where water naturally flows out of the ground. This comes from the German word 'springer,' which means 'to leap from the ground. Springs Form from Aquifers. There are two types of aquifers: confined and unconfined. Confined aquifers are sandwiched between two layers of low permeability soil. This means that the water coming into the ground does not flow directly into or out of the aquifer since the soil around it doesn't allow much water to pass through. All aquifers are at least partially unconfined aquifers because they wouldn't be filled with water if they didn't have a source feeding them! These aquifers are underneath permeable soil layers, so water easily trickles through the ground into the aquifer. A spring is formed when the pressure in an aquifer causes some of the water to flow out at the surface. This usually happens at low elevations, along hillsides or at the bottom of slopes. Some springs are just tiny trickles of water seeping from the ground, while others are large enough that they create rivers or lakes.
Types of springs Springs are named for how they flow, and there are five main types. The first type of spring is a gravity spring. This is just what it sounds like - these form from the pull of gravity. The water gets pulled down through the ground until it reaches a layer it can't penetrate. Because it has nowhere else to go, it starts flowing horizontally until it reaches an opening and water comes out as a spring. These are usually found along hillsides and cliffs. Next, we have artesian springs, which come from pressure in confined aquifers forcing the water to the surface. The pressure inside the confined aquifer is less than the pressure outside the aquifer, so the water moves in that direction. Any cracks or holes in the land will easily let the water escape. Our next type of spring is a seepage spring, which as you may have guessed, is groundwater seeping out at the surface. Seepage springs slowly let water out through loose soil or rock and are often found in land depressions or low in valleys. The fourth type of spring is a tubular spring. These springs occur in underground cave systems, which resemble underground highways. These tubes, or channels, are made of limestone, and as water moves through this type of rock, it dissolves some of it away. Tubular springs are some of the largest springs on Earth, and the tubes themselves can be so small that you can't see them or large enough to walk through! Finally, we have fissure springs. Fissures are just large cracks, so you can probably figure out that fissure springs occur along large cracks in the ground, like fault lines. Fissure springs are often used as a source of drinking water, and sometimes scientists go looking for fissure springs when they want to find a fault on earth.
Artesian Well
Fig. Artesian well Wells that tap these confined aquifers are "artesian wells". If altitude that the pressurized aquifer pushes water up a well tapping it is the "piezometric level". If this level is below the land surface altitude the water will not shoot out of the well at the land surface the well is called an artesian well. But if the piezometric level is higher than the well head altitude at the land surface the water will be pushed upward in the well and emerge at the land surface, with no pump needed. This kind of well is a flowing artesian well.
Geyser A geyser is a vent in Earth's surface that periodically ejects a column of hot water and steam. Even a small geyser is an amazing phenomenon; however, some geysers have eruptions that blast thousands of gallons of boiling-hot water up to a few hundred feet in the air.
Spring deposits Spring systems encompass a tremendous range of environmental niches where calcareous deposits commonly form. Although active springs have been classified according to their water temperature (cold to hot) or water source (thermogene and meteogene), such classifications are difficult to apply to (sub)fossil systems where water is no longer flowing. Although the deposits formed in these settings have long been referred to as tufa or travertine, the distinction between these terms has been largely debased through inconsistent usage.
The precipitation of calcite as opposed to aragonite in spring systems has been variously attributed to water composition, water temperature, growth inhibitors (e.g., Mg/Ca ratio), and/or CO2 degassing and saturation levels. In springs, the rate of CO2 degassing, a fundamental control on the degree of CaCO3 supersaturation, seems to exert considerable influence over carbonate precipitation as well as the morphology of crystals that form. Rapid CO2 degassing, for example, seems to be responsible for the precipitation of large, dendritic calcite crystals that characterize many spring deposits throughout the world. Siliceous deposits are much less common than the calcareous, because of the rare conditions under which silica is dissolved in any considerable quantity, hot solutions of alkaline carbonates being necessary for this purpose. Iron deposits are formed by the springs known as chalybeate, which contain the carbonate of iron (FeC08) in solution. Contact with the air speedily converts the soluble carbonate into the insoluble Fe203, which forms brown stains and patches on the channels leading from such springs, and considerable quantities of it collect in pools. Here again, organic agency may supplement the chemical work, for certain diatoms extract iron from the water, as other Algae extract lime and silica.
Aquifer An aquifer is a body of porous rock or sediment saturated with groundwater. Groundwater is the word used to describe precipitation that has infiltrated the soil beyond the surface and collected in empty spaces underground. Groundwater enters an aquifer as precipitation seeps through the soil. It can move through the aquifer and resurface through springs and wells. There are two general types of aquifers: confined and unconfined. Confined aquifers have a layer of impenetrable rock or clay above them, while unconfined aquifers lie below a permeable layer of soil. Many different types of sediments and rocks can form aquifers, including gravel, sandstone, conglomerates, and fractured limestone. Aquifers are sometimes categorized according to the type of rock or sediments of which they are composed. A common misconception about aquifers is that they are underground rivers or lakes. While groundwater can seep into or out of aquifers due to their porous nature, it cannot move fast enough to flow like a river. The rate at which groundwater moves through an aquifer is varies depending on the rock’s permeability. Much of the water we use for domestic, industrial, or agricultural purposes is groundwater. Most groundwater, including a significant amount of our drinking water, comes from aquifers. In order to access this water, a well must be created by drilling a hole that reaches the aquifer. While wells are manmade points of discharge for aquifers, they also discharge naturally at springs and in wetlands.
Geological work of groundwater Groundwater plays an important role in many geologic processes. For example, the fluid pressures that build up on faults are now recognized to have a controlling influence on fault movement and the generation of earthquakes. On another front, subsurface flow systems are responsible for the transfer of heat and chemical constituents through geologic systems, and as a result, groundwater is important in such processes as the development of geothermal systems, the thermodynamics of pluton emplacement, and the genesis of economic mineral deposits. At depth, groundwater flow systems control the migration and accumulation of petroleum. Nearer the surface, they play a role in such geomorphologic processes as karst formation, natural slope development, and stream bed erosion.
Solution A solution is a homogeneous mixture of two or more components in which the particle size is smaller than 1 nm. Common examples of solutions are the sugar in water and salt in water solutions, soda water, etc. In a solution, all the components appear as a single phase. There is particle homogeneity i.e. particles are evenly distributed. This is why a whole bottle of soft drink has the same taste throughout. Liquid solutions, such as sugar in water, are the most common kind, but there are also solutions that are gases or solids. Any state of matter (solid, liquid, or gas) can act both as a solute or as a solvent during the formation of a solution. Therefore, depending upon the physical states of solute and solvent, we can classify in nine different types of solutions.
Karst topography It is a landscape that is characterized by numerous caves, sinkholes, fissures, and underground streams. Karst topography usually forms in regions of plentiful rainfall where bedrock consists of carbonate-rich rock, such as limestone, gypsum, or dolomite, that is easily dissolved. Surface streams are usually absent from karst topography. Throughout the world karst landscapes vary from rolling hills dotted with sinkholes, as found in portions of the central United States, to jagged hills and pinnacle karst found in the tropics. The development of all karst landforms requires the presence of rock which is capable of being dissolved by surface water or ground water. The term karst describes a distinctive topography that indicates dissolution (also called chemical solution) of underlying soluble rocks by surface water or ground water. Although commonly associated with carbonate rocks (limestone and dolomite) other highly soluble rocks such as evaporates (gypsum and rock salt) can be sculpted into karst terrain. Understanding caves and karst is important because ten percent of the Earth’s surface is occupied by karst landscape and as much as a quarter of the world’s population depends upon water supplied from karst areas. Though most abundant in humid regions where carbonate rock is present, karst terrain occurs in temperate, tropical, alpine and polar environments. Karst features range in scale from microscopic (chemical precipitates) to entire drainage systems and ecosystems which cover hundreds of square miles, and broad karst plateaus.
Development of karst features Karst is most strongly developed in dense carbonate rock, such as limestone, that is thinly bedded and highly fractured. Karst is not typically well developed in chalk, because chalk is highly porous rather than dense, so the flow of groundwater is not concentrated along fractures. Karst is also most strongly developed where the water table is relatively low, such as in uplands with entrenched valleys, and where rainfall is moderate to heavy. This contributes to rapid downward movement of groundwater, which promotes dissolution of the bedrock, whereas standing groundwater becomes saturated with carbonate minerals and ceases to dissolve the bedrock. Interstratal karst is a karstic landscape which is developed beneath a cover of insoluble rocks. Typically this will involve a cover of sandstone overlying limestone strata undergoing solution. In the United Kingdom for example extensive doline fields have developed at Cefn yr Ystrad, Mynydd Llangatwg and Mynydd Llangynidr in South Wales across a cover of Twrch Sandstone which overlies concealed Carboniferous Limestone, the last-named having been declared a site of special scientific interest in respect of it. Kegelkarst is a type of tropical karst terrain with numerous cone-like hills, formed by cockpits, mogotes, and poljes and without strong fluvial erosion processes. This terrain is found in Cuba, Jamaica, Indonesia, Malaysia, the Philippines, Puerto Rico, southern China, Myanmar, Thailand, Laos and Vietnam. Pseudokarsts are similar in form or appearance to karst features but are created by different mechanisms. Examples include lava caves and granite tors— for example, Labertouche Cave in Victoria, Australia—and paleocollapse features. Mud Caves are an example of pseudokarst. Paleokarst or palaeokarst is a development of karst observed in geological history and preserved within the rock sequence, effectively a fossil karst. There are for example palaeokarstic surfaces exposed within the Clydach Valley Subgroup of the Carboniferous Limestone sequence of South Wales which developed as sub- aerial weathering of recently formed limestones took place during periods of non- deposition within the early part of the period. Sedimentation resumed and further limestone strata were deposited on an irregular karstic surface, the cycle recurring several times in connection with fluctuating sea levels over prolonged periods. Karst areas tend to have unique types of forests. The karst terrain is difficult for humans to traverse, so that their ecosystems are often relatively undisturbed. The soil tends to have a high pH, which encourages growth of unusual species of orchids, palms, mangroves and other plants.
Characteristics of Karst regions Karst, terrain usually characterized by barren, rocky ground, caves, sinkholes, underground rivers, and the absence of surface streams and lakes. It results from the excavating effects of underground water on massive soluble limestone. The term originally applied to the Karst (or Kras) physiographic region, a limestone area northeast of the Gulf of Trieste in Slovenia, but has been extended to mean all areas with similar features. Conditions that promote karst development are well-jointed, dense limestone near the surface; a moderate to heavy rainfall; and good groundwater circulation. Limestone (calcium carbonate) dissolves relatively easily in slightly acidic water, which occurs widely in nature. Rainwater percolates along both horizontal and vertical cracks, dissolving the limestone and carrying it away in solution. Limestone pavements are produced by the removal of surface material, and the vertical fissures along joints are gradually widened and deepened, producing a grooved and jagged terrain. As it flows along cracks underground, the water continues to widen and deepen the cracks until they become cave systems or underground stream channels into which narrow vertical shafts may open. Most, but not all, of the principal cave areas of the world are areas of karsts. Features such as lapiés, natural bridges, and pepino hills are characteristic of karsts.
Origin of L.St. caverns Depositional features in limestone caverns can exhibit a wide variety of formations, out of which the most popularly known features are aggregations of calcium carbonate protruding from the ceilings, or from walls and floors. The many forms of deposits of such carbonate rocks can be described with the inclusive term cave travertine, although the term speleothems is also sometimes used. Limestone caverns often have water laced with calcium carbonate and other minerals dripping from the ceilings of these limestone caverns, which lead to certain formations in limestone caverns for which the pioneering American Geologist W.H. Davis (1930) proposed the term dripstone to describe them collectively. Those aggregations extending downwards are called stalactites and those growing upwards from surfaces are called stalagmites. These aggregations can also occur in the form of columns and pillars inside limestone caverns. These can occur in a multitude of shapes and sizes. Sometimes, these forms can appear in irregular outgrowths, growing obliquely, horizontally, with curvatures as well as downward for example. These are called helictites. Davis proposed two-cycle theory, in which limestone caverns are formed by the action of water below the water table instead of above. This takes place by the action of water in two stages or cycles. In the first cycle, phreatic water forms a solution for the dissolving processes that form a major part of the development of subterranean caverns. Phreatic water is water from the phreatic zone i.e. the area below the water table in an aquifer where all the pores and fractures in the soil are saturated with water.
Artesian belts of Tamilnadu Nearly 73% of the total area of the State is occupied by a variety of hard & fissured crystalline rocks like charnockite, gneisses and granites. The depth of open wells varies from 6 to 30mbgl, while the depth of borewells generally varies from 30-100mbgl. The sedimentary formations consist of sand stones, limestones and shales whereas Quaternary sediments in the State represented by Older alluvium and Recent alluvium and coastal sands. In the Cauvery delta of Thanjavur district, the artesian pressure head ranges between 4.5 to 17 mbgl with free flow up to 270 m3/hr. The yield of wells in the alluvium varies form 27 to 212 m3/hr. The yield of wells in the fissured formations varies from 7 to 35 m3/hr. The dependency on ground water has increased many folds during the recent years and the ground water extraction for irrigation, domestic and industries have resulted in lowering of water levels, long-term water level declining trend and even drying up of wells. In order to regulate the groundwater development, Central Ground Water Board in association with State Ground Water Department has computed Dynamic Groundwater Resources and categorized blocks as Over Exploited, Critical, Semi Critical and Safe. The net ground water availability for irrigation development has been computed as the difference between net annual ground water availability and the gross ground water draft including the allocation for domestic and industrial uses for the next twenty five years. The computation indicates that balance ground water potential is not available for future irrigation development in the major part of Coimbatore, Dharmaputi, Krishnagiri, Dindigul, Nagapattinam, Namakkal, Salem, Theni, Vellore and Tiruvannamalai districts as the ground water drafts in the districts mentioned have already exceeded the total available ground water resources for irrigation. The stage of ground water development in January 2004, computed as the ratio of gross ground water draft for all uses to net ground water availability ranged from 4 % in Nilgiris district to 149% in Dharmapuri district.
UNIT-4
Glaciers:
• A glacier is a thick mass of ice which moves over the ground under the influence of gravity.
• It is formed due to the compaction and recrystallization of snow.
Snow line:
• The snow line is the lower limit of accumulating snow.
• Below the snow line the snow melts in summer.
• The elevation of snowline varies considerably.
• In polar regions it may be at sea level, whereas in equator the snowline may occur at 6000meters.
• In the Himalayas the snowline lies at altitudes varying between 4200 to 5700 meters.
Types of glaciers:
There are three types of glaciers. They are
1.Valley glaciers
2.Piedmont glaciers
3.Ice sheet
1. Valley glaciers
The glaciers which originate near the crests of high mountains and move along the valleys just like rivers are called valley glaciers.
2. Piedmont glaciers:
At the end of the hilly region a number of valley glaciers may unite to form a comparatively thick sheet of ice. Such a compound glacier is called piedmont glacier.
3.Ice sheet
• These are massive accumulation of ice covering extensive areas.
• Two such glaciers that exist today are the Greenland and Antarctic ice sheets.
• The Greenland glaciers cover an area of about 1.7million square kilometers and is over 1500meter thick.
Movement of glaciers:
• Most of the glaciers move at a rate of a few meters per day.
• They move partly by plastic flow and partly by shear movements.
• In the high gradient valleys a mountain glacier flows down the slope much like a stream of water under gravity.
• This type of movement is called gravity flow.
• But in basin shaped, flat or upland areas where ice cannot move under gravity, the glaciers move as a result of differential pressure within them. • This type of movement is called extrusion flow.
• In a moving glacier two zones can be identified.
i)Zone of flow
ii)Zone of fracture
• The zone of flow is found in the deeper layer of ice. Here the weight of overlying ice is great and the ice behaves plastically.
• The upper layer of the ice have little pressure on them and therefore the surface ice behaves as brittle mass. It often develops cracks known as crevasses. This upper zone is known as zone of fracture.
Erosion:
Glacier cause erosion in three ways:
• Plucking or quarrying
• Abrasion
• Frost wedging
Plucking: When flowing over a jointed rock surface, the glacier ice adheres to blocks of jointed bedrock, pulls them out and carries them away.
Abrasion: The moving ice grinds and polishes the rock surface with the help of rock fragments which are held firmly within the body of the glacier. The abrasion produces striations and grooves in the bedrock surfaces.
Frost wedging: Thawing and freezing of water in the cracks and joints of rocks break them by wedge action. In this manner rock fragments of all sizes are added into the glacier.
Features of glacial erosion:
• Striations
• U-shaped valleys
• Hanging valleys
• Cirques
• Serrate ridges
• Roche moutonnees • Fiords
Striations:
Glaciers carry rock fragments firmly embedded in the ice. They scratch, grind or groove the rock surface over which they move. These scratches and grooves left on bedrock and boulders, are called striations. The striations indicate the direction of ice movement.
U-shaped valleys:
Glacier occupies valleys and flow down hills. As they erode their valleys both laterally and vertically, U shaped valleys with steep walls and flat floors are produced.
Hanging valleys:
Since the magnitude of the glacial erosion depends upon the thickness of the ice, main glaciers cut their valleys deeper than these of their tributaries. As a result, at the junction where a tributary joints the main glacier, the floors of their valleys do not meet at the same level. The valley of the tributary stands at a highest elevation than that of the main valley. Such valleys are called hanging valleys.
Cirques:
The bowl-shaped hollows present at the glacier valley heads in the mountains, are called cirques. They are formed mainly by the quarrying and frost-wedging action of ice. In cirques, a little gap is generally left between the bend of the glaciated valley and the mass of the glacier ice. This gap is known as the Bergschrund.
Serrate ridges:
As the adjacent cirques, along the opposite side of a mountain are enlarged, the space between them becomes narrow. As a result sharp divides are formed. Such divides which have jagged, serrated and linear crest are called serrate ridges. When three or more cirques surround a mountain summit, a pyramid-like peak is formed. Such a peak is called horn. A sharp edged ridge of rock formed between adjacent cirque glacier is called arete.
Roche Moutonnees: These are small mounds of resistant bedrock which have a typically asymmetrical appearance. The side facing the direction of ice advance is gentle and smooth, while the leeward side is steep and rough. This form results from the plucking action on the leeward side and abrasion on the opposite side.
Fiords:
The glaciers that descend from coastal mountains may cut their valleys below sea level. Such valleys produces fiords. Fiords are highly over-deepened narrow channels of glacial origin along which the sea encroaches inland. Fiords are found along many coasts including those of Norway, British Columbia and Alaska.
TRANSPORTATION: Glaciers acquire a huge amount of rock debris by plucking, abrasion and frost wedging. This material is transported in three ways.
1. Super glacial load
2. Englacial load
3. Subglacial load
1. Super glacial load: The debris that falls from the valley walls on the surface of the glacier, is transported as a conveyer belt. Such debris is called super glacial load. 2. Englacial load: Sooner or later a part of the debris is engulfed into crevasses. This material which is enclosed within the ice is called englacial load. 3. Subglacial load: The debris present at the bottom of the glacier is called subglacial load. The subglacial load includes the material plucked from the rocky floor and a portion of the debris that reaches the base from the above.
DEPOSITIONAL LANDFORMS OF GLACIERS
MORAINS:
Ridges or layers of till are called moraines they are of four types:
1. Ground moraines
2. Lateral moraines
3. Medial moraines
4. Terminal moraines
1. Ground moraines: A layer of till deposited beneath the moving ice on the ground is called the Ground moraine. Ground moraines fill low spots and old stream channels thereby creating a levelling effect. 2. Lateral moraines: The material that falls from the valley walls, accumulates materials are left as ridges along the sides of a glacier. When the glacier disappears, these materials are left as ridges along the sides of the valley. Such deposits are called lateral moraines.
3. Medial moraines: When two glaciers meet a medial moraine is formed by the union of two lateral moraines.
4. Terminal moraines: At the terminus of a glacier where the ice starts melting, the rock debris is deposited in the form of a ridge which extends across the valley. Such deposits are called terminal moraines or end moraines.
Outwash plains
• In front of the end moraines, streams of melt water deposit sediment producing stratified deposits of sand, silt and gravel. Such deposits constitute “outwash plains”.
Kettle holes
• These are basin-like depressions found in areas of both till and outwash plains. The diameter of kettle holes ranges from a few meters to a few kilometers. They commonly contain water. These depressions are created when the masses of buried ice melt.
Drumlins
• “Drumlins” are small, smooth, elliptical hills of till that lie parallel to the direction of ice movement. Unlike Roche moutonnees the uphill sides of the drumlins are steep and the downhill sides are gently sloping.
• They may be 20-30 meters high and a kilometer long. Drumlins are not found singly but they occur in clusters thereby forming drumlin fields. They are believed to have formed by a sub glacial shaping of an accumulated till into streamlined forms.
Eskers:
• Eskers are long winding ridges of stratified drift found in the middle of ground moraines.
• They run for kilometers in a direction more or less parallel to the direction in which ice moved. • Eskers are formed due to deposition of gravels and sand by the englacial and subglacial streams.
• In many areas they are mined for sand and gravel.
Kames:
• Kames are hillocks of stratified drift which are formed at the edge of the retreating ice by glacial streams.
• These streams fall from a height and deposit sand and gravel along the margin of the glaciers as alluvial cones.
Varves:
• Varves are thinly laminated deposits formed in glacial lakes.
• They consist of alteration of light colored bands of silt and dark colored bands of clays.
• The former gets deposited during the summer season while the later in winter.
• Thus each pairs of varves corresponds to one year of deposition.
• This thickness of a varve may vary from a very small fraction of a centimeter to 0.75 centimeter.
Buried valley:
• Buried valleys are the ancient deep valleys which are excavated in the bedrock by glacial erosion and are filled back subsequently with glacial drift.
• The present day surface topography gives no clue to their existence.
• The rivers which are flowing in these areas may have no relation to the buried valley.
Such valleys create unexpected problems for the civil engineers.
ICE AGE
The Pleistocene epoch is called an ice age. The ice age began at least 2.5 million years ago and had duration perhaps of a million years. The most recent retreat of ice had taken place between 10,000 and 15,000 years ago. The areas which were extensively buried by ice sheets included northern North America, Northern Europe and NW Asia in this areas ice sheets do not exist today.
The Pleistocene Epoch however was not a period of continuous glaciation. During this period the continental glaciers alternately advanced and retreated the time spans between glacial advances are called interglacial period. Some of the interglacial period lasted longer than the glacial one. Four major periods of glacial advance and retreat have been identified in North America and up to 6 in Europe
LAKES:
• A lake is a body of water of considerable size, localized in a basin, that is surrounded by land apart from a river or other outlet that serves to feed or drain the lake. • Lakes lie on land and are not part of the ocean, and therefore are distinct from lagoons, and are also larger and deeper than ponds.
• Natural lakes are generally found in mountainous areas, rift zones, and areas with ongoing glaciation.
• Most lakes have at least one natural outflow in the form of a river or stream, which maintain a lake’s average level by allowing the drainage of excess water
• Other lakes are found in endorheic basins. Some lakes do not have a natural outflow and lose water solely by evaporation or underground seepage or both. They are termed endorheic lakes.
• The majority of lakes on Earth are fresh water, and most lie in the Northern Hemisphere at higher latitudes. Canada, Finland and Siberia contain most of the fresh water lakes.
Classification of lakes:
1. Temporary lakes
2. Permanent lakes
3. Fresh water lakes
4. Saline water lakes
Temporary lakes
• Lakes may exist temporarily filling up the small depressions of undulating ground after a heavy shower.
• In this kind of lakes, Evaporation > Precipitation.
• Example: Small lakes of deserts.
Permanent lakes
• In this kind of lakes, Evaporation < Precipitation.
• These lakes are deep and carry more water than could ever be evaporated.
• Example: Great Lakes of North America, East African Rift Lakes.
Fresh water lakes • Most of the lakes in the world are fresh-water lakes fed by rivers and with out- flowing streams e.g. Great Lakes of North America.
Saline lakes
• Salt lakes (also called saline lakes) can form where there is no natural outlet or where the water evaporates rapidly and the drainage surface of the water table has a higher-than-normal salt content.
• Because of the intense evaporation (negative freshwater balance more water is lost in evaporation than gained from rivers) these lakes are saline.
• Examples of salt lakes include Great Salt Lake, the Aral Sea and the Dead Sea.
• For example the Dead Sea has a salinity (salt content) of 250 parts per thousand, and the Great Salt Lake of Utah, U.S.A. has a salinity of 220 parts per thousand.
• Playas or salt lakes, are a common feature of deserts (recall desert landforms).
Lakes Formed by Earth Movement
1. Tectonic lakes
2. Rift valley lakes
Tectonic lakes
• Due to the warping (simple deformation), subsidence (sliding downwards), bending and fracturing (splitting) of the earth’s crust, tectonic depressions occur. (We have studied all these terms in previous posts)
• Such depressions give rise to lakes of immense sizes and depths.
• They include Lake Titicaca, and the Caspian Sea.
Rift valley lakes
• A rift valley is formed when two blocks of earth move apart letting the ‘in between’ block slide downwards. Or, it’s a sunken land between two parallel faults. • Rift valleys are deep, narrow and elongated. Hence the lakes formed along rift valleys are also deep, narrow and very long.
• Water collects in troughs (Valley in the rift) and their floors are often below sea level.
• The best known example is the East African Rift Valley which runs through Zambia, Malawi, Tanzania, Kenya and Ethiopia, and extends along the Red Sea to Israel and Jordan over a total distance of 3,000 miles.
• It includes such lakes as Lakes Tanganyika, Malawi, Rudolf, Edward, Albert, as well as the Dead Sea 1,286 feet below mean sea level, the world’s lowest lake.
Lakes Formed by Glaciation
1. Cirque lakes or tarns
2. Rock-hollow lakes
Cirque lakes or tarns
• Cirque is a hollow basin cut into a mountain ridge. It has steep sided slope on three sides, an open end on one side and a flat bottom.
• When the ice melts, the cirque may develop into a tarn lake.
Rock-hollow lakes
• The advance and retreat of glaciers can scrape depressions in the surface where water accumulates; such lakes are common in Scandinavia, Patagonia, Siberia and Canada.
• These are formed by ice-scouring (eroding) when ice sheets scoop out (dig) hollows on the surface.
• Such lakes of glacial origin are abundant in Finland – Land of Lakes. It is said that there are over 35,000 glacial lakes in Finland.
Lakes due to morainic damming of valleys
• Valley glaciers often deposit morainic debris across a valley so that lakes are formed when water accumulates behind the barrier.
Lakes Formed by Volcanic Activity 1. Crater and caldera lakes
Crater and caldera lakes
• During a volcanic explosion the top of the cone may be blown off leaving behind a natural hollow called a crater.
• This may be enlarged by subsidence into a caldera.
• In dormant or extinct volcanoes, rain falls straight into the crater or caldera which has no superficial outlet and forms a crater or caldera lake.
• Examples: Lonar in Maharashtra and Krakatao in Indonesia.
Lakes Formed by Erosion
1. Karst lakes
2. Wind-deflated lakes
Karst lakes
• The solvent action of rain-water on limestone carves out solution hollows. When these become clogged with debris lakes may form in them.
• The collapse of limestone roofs of underground caverns may result in the exposure of long, narrow- lakes that were once underground.
Wind-deflated lakes
• The winds in deserts creates hollows. These may reach ground water which seeps out forming small, shallow lakes. Excessive evaporation causes these to become salt lakes and playas. Example: Great Basin of Utah, U.S.A.
Lakes Formed by Deposition
1. Lakes due to river deposits
2. Lakes due to Marine deposits
Lakes due to river deposits
• Ox-bow lake, e.g. those that occur on the flood-plains of Lower Mississippi, Lower Ganges etc.. Lakes due to Marine deposits
• Also called Lagoons.
• Example: Lake Chilka
Man-made lakes:
• Besides the natural lakes, man has now created artificial lakes by erecting a concrete dam across a river valley so that the river water can be kept back to form reservoirs.
• Example: Lake Mead above the Hoover Dam on the Colorado River, U.S.A.
• Man’s mining activities, e.g. tin mining in West Malaysia, have created numerous lakes. Inland fish culture has necessitated the creation of many fishing-lakes.
UNIT-5
WAVES, TIDES AND CURRENTS
Waves
A disturbance which moves through or over the surface of a fluid is known as waves. Mostly waves are raised by winds also earthquakes, volcanoes and gravity pull. Waves form a great energy.
Parts of waves:
Crest: The highest point of the wave is called crest.
Trough: The lowest point of the wave is called trough.
Wave height: The vertical distance from crest to trough is called wave height.
Wave length: The horizontal distance between crest to crest or trough to trough is called as wave length.
Size of waves:
The size of waves depends on two things
I. Wind speed
II. Wind duration
Importance of waves:
1. Shaping coast lines
2. Grind rock into sand
3. Erode cliff
4. Ecology
a) Returns oxygen to water
b) Steer up food for filter
Types of waves:
1. CHOP: The short period wave is known as chop.
2. SWELL: The long period wave is known as swell.
3. SWASH: The waves moving up to the beach is known as swash.
4. BACK SWASH: The waves moving back down is known as backswash
Tides: The rhythmic rise and fall of the oceans water is known as tides.
High tide: Water rising is known as high tide.
Low tide: Water receding is known as low tide.
Types of tides:
1. Spring tide: If moon and sun are in direct line with one another. Then it is known as spring tides. These tides results usually high tidal range.
2. Neap tide: If the sun and moon are at right angles then it is known as neap tide. These tides usually have low tidal range.
Distance between moon and earth:
Perigee tide: If the moon is closest to Earth then it is known as perigee tides. It results in very high tide.
Apogee tide: If the moon is farthest away from earth it is known as apogee tides. It results in very low tides.
Rise and fall of water per day:
Diurnal tides: If the water have one high and one low tide per day then it is known as diurnal tides.
Example: parts of gulf of Mexico and Asia Semi-diurnal tides: If the water have two high tide and two low tide per day then it is known as semi-diurnal tides.
Example: Atlantic coasts of North America and Europe
Mixed tides: If the water have two high and two low tide per day and the height varies is known as mixed tide.
Example: Pacific coast
Uses:
1. Circulates water in bays and estuaries.
2. Circulate food, waste etc.
Currents:
The river of circulating water is known as currents.
Causes:
1. Wind
2. Rotating earth
Surface ocean currents:
➢ Surface ocean currents are broad, slow drift. ➢ It is wind generated.
➢ It do not cross equator.
Coriolis effects:
➢ In Northern hemisphere it rotates clockwise (right).
➢ In Southern hemisphere it rotates anti-clockwise (left)
Longshore current:
➢ The current flowing parallel to shore is known as longshore current. This current moves sediments.
Rip current:
➢ It is caused by converging longshore current
➢ It is very dangerous. ➢ If caught in rip current swim parallel to shore to get out of channel.
Deep ocean current:
➢ Deep ocean current flow beneath the surface.
➢ It cross equator.
➢ It moves north to south.
Importance:
➢ Upwelling
➢ Brings deep water to surface
➢ Circulates nutrients
➢ Moves plankton and larval
SHORELINE AND IT’S CLASSIFICATION
Shoreline
The shoreline is the line of demarcation between land and water. It fluctuates from moment to moment by waves and tides.
Shoreline of emergence
These are formed either by an upliftment of the and or by lowering of the sea level. This type of coast has bars, spits, lagoons, beaches, sea cliff and arches. The east coast of India especially is south eastern part appears to be a coast of emergence.
Shoreline of submergence
A submerged coast is produced either by subsidence of land or by a rise in sea level West coast of India appears to be a coast of submergence.
Neutral shoreline
These are coastlines formed as a result of new materials being built into the water. The word neutral implies that their need to be no relative changes between the level of sea and the coastal region of the continent.
Compound shoreline
Such coastlines show the form of the previous coastlines that is coastline of submergence and coastline of emergence combined. For example submergence followed by emergence or vice versa.
Example: coastline of Norway, Sweden
Fault shoreline
Such coastlines are unusual features and result from the submergence of a downthrown blow along a fault, such that the uplifted block has its steep side or the fault line standing against the sea forming a fault coastline.
CONTINENTAL MARGIN
Continental shelf:
• Continental shelf, a broad, relatively shallow submarine terrace of continental crust forming the edge of a continental landmass. The geology of continental shelves is often similar to that of the adjacent exposed portion of the continent, and most shelves have a gently rolling topography called ridge and swale. Continental shelves make up about 8 percent of the entire area covered by oceans.
• A continental shelf typically extends from the coast to depths of 100–200 meters (330–660 feet). It is gently inclined seaward at an average slope of about 0.1°. In nearly all instances, it ends at its seaward edge with an abrupt drop called the shelf break.
• The average width of continental shelves is about 65 km (40 miles).
• The world’s largest continental shelf extends 1,500 km (about 930 miles) from the coast of Siberia into the Arctic Ocean.
• Continental shelves are usually covered with a layer of sand, silts, and silty muds.
Continental slope:
Continental slope, seaward border of the continental shelf. The world’s combined continental slope has a total length of approximately 300,000 km (200,000 miles) and descends at an average angle in excess of 4° from the shelf break at the edge of the continental shelf to the beginning of the ocean basins at depths of 100 to 3,200 meters.
• The transition from continental crust to oceanic crust usually occurs below the continental slope.
• About 8.5 percent of the ocean floor is covered by the continental slope-rise system. This system is an expression of the edge of the continental crustal block.
The predominant sediments of continental slopes are muds; there are smaller amounts of sediments of sand or gravel. The continental slopes are temporary depositional sites for sediments.
Continental rise:
Continental rise, a major depositional regime in oceans made up of thick sequences of continental material that accumulate between the continental slope and the abyssal plain.
This feature can be found all around the world, and it represents the final stage in the boundary between continents and the deepest part of the ocean.
Abyssal plain:
Abyssal plain, flat seafloor area at an abyssal depth (3,000 to 6,000 m [10,000 to 20,000 feet]), generally adjacent to a continent.
Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains are among the flattest, smoothest and least explored regions on Earth.
Submarine canyon:
Submarine canyon, any of a class of narrow steep-sided valleys that cut into continental slopes and continental rises of the oceans.
Submarine canyons originate either within continental slopes or on a continental shelf.
They are rare on continental margins that have extremely steep continental slopes or escarpments.
Submarine canyons are so called because they resemble canyons made by rivers on land.
Formation of submarine canyons Sea mount:
Seamount, large submarine volcanic mountain rising at least 1,000 m (3,300 feet) above the surrounding deep-sea floor; smaller submarine volcanoes are called sea knolls, and flat-topped seamounts are called Guyots.
The summits and flanks of seamounts are generally covered with a thin layer of marine sediment.
Seamounts are exceedingly abundant and occur in all major ocean basins.
By the late 1970s more than 10,000 seamounts had been reported from the Pacific Ocean basin alone.
Guyots:
Guyots are seamounts that have built above sea level. Erosion by waves destroyed the top of the seamount resulting in a flattened shape. Due to the movement of the ocean floor away from oceanic ridges, the sea floor gradually sinks and the flattened Guyots are submerged to become undersea flat-topped peaks.
Guyot, also called table mount, isolated submarine volcanic mountain with a flat summit more than 200 meters (660 feet) below sea level. Such flat tops may have diameters greater than 10 km (6 miles).
A volcano erupts above sea level somewhere in the ocean
After a long time, waves have eroded the portion above sea level.
A Gradually the sea floor subsides as it moves away from the oceanic ridge, and the Guyot becomes submerged.
FORMATION OF GUYOT Mid-oceanic ridges:
Oceanic ridge, continuous submarine mountain chain extending approximately 80,000 km through all the world’s oceans.
Individually, ocean ridges are the largest features in ocean basins.
They can be thousands of kilometers wide.
Trenches:
Deep-sea trench, also called oceanic trench, any long, narrow, steep-sided depression in the ocean bottom in which occur the maximum oceanic depths, approximately 7,300 to more than 11,000 meters (24,000 to 36,000 feet).
They typically form in locations where one tectonic plate subducts under another. The deepest known depression of this kind is the Mariana Trench, which lies east of the Mariana Islands in the western North Pacific Ocean; it reaches 11,034 meters (36,200 feet) at its deepest point.
CORAL REEFS:
Coral reefs are island like structures found in the ocean. They are built by corals and many other lime secreting marine organisms under tropical and subtropical climatic conditions. They occur mainly in the warm water of the Pacific and Indian oceans.
The conditions which favor the development of coral reefs are as follows
❑ Reef building corals grow best in waters with an average annual temperature of about 24 degree Celsius. Cora reefs, therefore, develop only between 28 degree North and 28 degree South latitudes.
❑ Corals can not grow at depths where sunlight can not penetrate. This limits the depth of active coral reef growth to about 45 meters.
❑ Clear water is necessary for the growth of corals They do not survive in muddy water.
Types of corals:
Coral reefs are of three types:
I. Fringing reefs
II. Barrier reefs
III. Atolls I. Fringing reefs: A fringing reef is formed on the margin of an island in continuity with the shore. It encircles the island almost completely.
II. Barrier reef: Barrier reefs are built away from the island and therefore they enclose a lagoon between the central landmass and themselves. The great barrier reef along the northeast coast of Australia is the famous example of this type.
III. Atolls: An atoll is a circular reef the central portion of which is occupied by relatively shallow lagoon.
Origin of coral reefs:
The formation of coral reefs was explained by Charles Darwin in 1836 He said that coral reefs form on the flanks of sinking volcanic islands. Darwin’s theory is known as “subsidence theory”. This theory is still considered to be a most probable explanation.
It may be summarized as follows
1. The process starts with the formation of a volcanic island on the sea floor. The corals grow around the edge of the volcanic island and build a fringing reef.
2. Then the island slowly sinks beneath the sea as a result of some tectonic movement. The actively growing corals may keep pace with this sinking and continue to build the reef upwards and outwards. In this way barrier reef is formed which is separated from the island by a lagoon.
3. With further subsidence, the central island disappears below the sea level and an atoll is formed.
GEOLOGICAL WORK OF SEA
EROSION BY SEA
Forces that shape coasts are: 1)erosion caused by sea waves,2)transportation of the rock debris, and 3)tectonic forces that causes uplift or subsidence of the coastal lands. The major agent of erosion at the shoreline is sea waves. They causes erosion in four ways:1)hydraulic impact,2)abrasion 3)attrition, 4)chemical action
1. Hydraulic impact: The impact force of high waves breaking against a rocky cliff during a storm can be very great. This force is enough to dislodge blocks of rocks as well as to enlarge preexisting fractures.
2. Abrasion: The sea waves become more destructive when they pick up rock fragments like pebbles and sands, and strike them against the cliffs. A great deal of erosion is done in this way.
3. Attrition: The pebbles and sands moving to and fro along with the sea waves are further broken down to smaller sizes due to mutual collision.
4. Chemical action of water: The physical destructiveness of the waves is enhanced greatly by the chemical action of sea water. The chemical decay extends and widens the cracks in rocks and prepares them for the disintegration by waves. The chemical action of sea water is particularly seen where coasts are composed of readily soluble rocks, such as limestones and dolomites.
Eroded soft rocks Erosional landforms:
➢ Wave cut cliff
➢ Wave cut bench
➢ Sea arch and sea stack
Wave cut cliff:
The sea waves dash the rocky shore and cut it actively. Due to continuous erosion at the base of coastal land, a cliff is formed. This cliff is called wave cut cliff.
Wave cut bench:
The sea waves undercut the cliffs and produce a notch at the base. This causes the overhanging rocks to fall into the water. In this way the cliff gradually retreats towards land leaving a submerged rocky platform which is called wave cut bench.
Sea arch and sea stack:
Sea caves: Headlands that extend into the sea are vigorously attacked by the waves. The waves erode the rock selectively thereby destroying the softer or more highly fractured rocks at the fastest rate. At first cave like features are produced at the base of the cliff which are called “sea caves”.
Sea arch: When two caves on opposite sides of a headland unite a gateway like structure is formed. Such a structure is called “sea arch”.
Sea stack: When the arch falls, a pillar like structure of rocks is left standing in the sea. Such a remnant pillar of rock is called “sea stack”
SEA CAVES
SEA ARCHES SEA STACK
Transportation by sea:
Beach material can be moved in four different ways. These are:
• Solution - when minerals in rocks like chalk and limestone are dissolved in sea water and then carried in solution. The load is not visible.
• Suspension - small particles such as silts and clays are suspended in the flow of the water.
• Saltation – where small pieces of shingle or large sand grains are bounced along the sea bed.
• Traction – where pebbles and larger material are rolled along the sea bed. Sediment is carried by the waves along the coastline. The movement of the material is known as longshore drift. Waves approach the coast at an angle because of the direction of prevailing wind. The swash will carry the material towards the beach at an angle. The backwash then flows back to the sea, down the slope of the beach. The process repeats itself along the coast in the zigzag movement.
Depositional features:
1. Beach
2. Wave built terrace
3. Spits
4. Sand bars
5. Tombolo
1.Beach: A beach is the flat mass of sand and gravel that is deposited on sea shores. A sediment of the beach is derived from erosion of adjacent cliffs and form alluvium contributed by rivers
2. Wave built terraces:
Under suitable conditions a part of the sediment is carried beyond the rock beach and is deposited there. In this way a flat platform like feature is formed which is called “wave built terrace”. Towards shore it merges with the beach.
3. Spits:
Where a straight shoreline takes a sharp turn, the longshore current are not able to flow parallel to it. Such a shore directs the currents into water of increasing depth, where deposition takes place. This results in the formation of a submerged bar, one end of which is attached to the main land. This bar is called “Spit”. The end of the spit often becomes curved landward in response to the wave action. Such a spit is called “hooked spit” or “hook”.
4. Sand bars:
Sand bars are the low offshore ridges of sand which extend parallel to the coast. The commonly enclose a lagoon.
5. Tombolo:
In the lee side of islands spits are often formed. If such a ridge connects an island to the main land or joins two islands together, it is called a “tombolo”.
OCEAN DEPOSITS
On the basis of their origin, the sea floor sediments may be classified into three groups:
i. Terrigenous sediment
ii. Biogenous sediment
iii. Hydrogenous sediment i. Terrigenous sediment: The most common sediment that covers deep ocean floor, is grey and brownish mud. This mud mainly consists of mineral grains derived from the erosion of land. ii. Biogenous sediment: This sediment is derived mainly from the shells and skeletons of marine animals and plants. “Calcareous ooze” is the most common biogenous sediment. This sediment is produced by organisms that live in the surface waters of the sea. Other biogenous sediments include “siliceous ooze” and phosphate rich materials. Oozes of silica are derived from the silica shells of diatoms (single celled algae), and radiolaria (single celled animals). The phosphate rich sediment is formed due to accumulation of bones, teeth and scales of fishes and other animals. iii. Hydrogenous sediment: This sediment contains minerals that crystallize directly from sea water through various chemical processes. For example, some limestone is formed in this way From economic point of view, “manganese nodules” are the most important hydrogenous sediment. These rounded, blackish, potato sized nodules contain a complex mixture of minerals which include Mg, Fe, Cu, Ni and Co.
TSUNAMI:
Tsunami is a Japanese word. ‘Tsu’ means harbor ‘nami’ means waves.
• Tsunamis are giant sea waves produced by earthquakes on the sea floor.
• They cause heavy destruction in areas lying near the sea shore.
• As sea tsunamis have wave lengths as great as 200 kilometers.
• They can travel at speeds of 800km per hour.
• As the tsunami approaches the shore, the sea withdraws and then it rushes back in a series of giant waves that travel far inland and cause destruction.
Causes of tsunami
Seismic activities:
The sea floor abruptly deforms and displaces the sea water lying above. Large vertical movements of earth's crust can occur at Plate boundaries which are called faults.
Volcanic eruption:
Volcanic eruptions create disturbance undersea by creating great force and thus generate tsunami.
Submarine landslides
When there is large landslide in mountains in the sea, the tsunami is caused and effects fell at bays.
Cosmic impacts:
When a meteorite or an alien force impact the ocean area disturbing the water from above, tsunami is caused.
Effects of tsunami:
1.Damaging property
2.Loss of life
3.Flooding
4.Contamination of water and soil
5.Fires from ruptured tanks or gas lines
6.Environmental impacts 1. Solid wastes and disaster debris 2. Radiation from nuclear plants 7.Psychological effects • Post Traumatic Stress Disorder (PTSD)
Origin of Tsunami:
• Tsunami waves originate with the occurrence of a forceful vertical motion that causes the water column to fall or rise suddenly, comparable to the wave that is formed when a hand is plunged abruptly into water. Tsunamis are most commonly triggered by earthquakes that result from the motion of continental plates.
• If the continental plates simply slide horizontally against one another without one being thrust above the other, however, the overlying water column does not receive the strong vertical impulse necessary to create such a wave. But if the plates rise or fall relative to one another, the water surface is correspondingly lifted or lowered, thus producing a tsunami. These kinds of motions occur most commonly in the vicinity of subduction zones, where one continental plate is thrust beneath another.
• Formation of a tsunami, therefore, does not depend necessarily on the intensity of an earthquake. There have been earthquakes measured with magnitudes of 8 or 9 that did not trigger tsunamis. By contrast, relatively weak earthquakes have been known to produce large tsunamis.
• Sophisticated computer models are now being applied in attempts to better understand the special characteristics of earthquakes that are particularly relevant to the development of tsunamis.
• Unlike waves at the water surface, which are produced by wind, a tsunami wave involves motion through the entire water column continuously from the site of its origin. At great depths it can propagate unimpeded, and at a water depth of 5000 meters can attain speeds of up to 800 kilometers per hour. The character of its propagation can be described with some confidence using mathematical-physical wave models.
• But when the wave encounters a continental slope or the shore, its progress is slowed, causing it to rise up vertically. How the tsunami develops from this point on depends upon the shape of the coast, and is much more difficult to describe mathematically. It is therefore almost impossible to accurately predict the wave height when it strikes land.
• Before a tsunami hits a coast, the water there initially retreats. This sequence of retreating water and surging surf can also be observed in the normal wave motion on a beach, whereby this motion is, of course, significantly smaller.
1. Through a vertical motion of the continental plates a pressure impulse is produced in water column. 2. The impulse propagates as a tsunami through the ocean. 3. When the wave nears the shore, it is slowed down and rises vertically.
Distribution of tsunamis: Tsunamis occur most often in the Pacific Ocean and Indonesia because the Pacific Rim bordering the Ocean has a large number of active submarine earthquake zones. However, tsunamis have also occurred recently in the Mediterranean Sea region and are expected in the Caribbean Sea as well.