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UNIT 1 - Major Land and Water Forms

Chapter 1 - Landform Patterns and Processes

Topography · the natural and human features of the Earth’s surface. ie. Surface

features · need to understand difference between relief and elevation · elevation - the height of a particular point of land above sea level · relief - the change in elevation over a given distance

Hill

- areas of high relief with elevations no higher than 300 - 600 m - isolated features

Mountain

- areas of high relief with elevations higher than 300 - 600 m

- most occur in long linear chains called ranges (usually along margins of continents)

Plain

- a level tract of land - frequently found along coastal areas

or at lower elevations - very gentle slope and no local a relief

for thirty metres or more Plateau

· an extensive, relatively flat upland area · have been raised upward into higher elevations by movements of

the Earth’s crust · often found in interiors of continents · because they are often deeply eroded by stream valleys, they

have more rugged appearances than plains

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Plate Tectonics and Continental Drift · Originally a theory by German scientist Alfred Wegener

· Believed at one point in the earth’s history we were one giant

‘supercontinent’ known as Pangea.

· The theory was backed up based on how the continents of Africa and South America fit together, many similar ferns and reptiles in many different continents,and same types of rocks on continents close to each other (yet separated by an ocean)

· But Wegener had an issue trying to explain what actually moved the

continents,

· The theory was polished in the 1960’s by J. Tuzo Wilson and the discovery of plate tectonics occurred. The idea that earth is made up of many tectonic plates and they can consist of continents, oceans, or both.

· Tectonic plates move or float on top of the upper mantle.

· However they do not float freely.

· The plates are forced in specific directions by the flow of magma

beneath.

· Plates move with the flow of magma.

· The magma closer to the core heats and then rises towards the surface as its density decreases.

· Once the rising magma reaches the lithosphere it moves in opposite

directions.

· The magma forms convectional currents. This then is the power that moves the tectonic plates.

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Compressional force

· a force pushing into a part of the earth’s crust, causing it to buckle plates move towards one another, squeezing together

· subduction zones sometimes form along these areas Tensional force

· a stretching force in the earth’s surface which may cause faulting · plates break apart, moving away from or past each other, which may

form a trench as one plate drops downward · ridge zones sometimes occur where two plates move apart. Magma

may rise between the plates and form a ridge

Mountain building Fold Mountains

- an upland area formed by the buckling of earth’s crust. Many fold mountains are associated with destructive or collision margins of plates.

- amount and extent of force and pressure, can create simple or complex forms.

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Anticline

- An arch-like upfold in buckled, bent, or contorted rock.

- looks like the letter ‘A’ Syncline

- a downfold of rock layers. - looks like a ‘S’mile

Mountains Formed by Faulting Faulting - A fracture in a rock formation along which there has been movement of the blocks of rock on either side of the plane of fracture. Normal Fault A fault in which rocks have moved down the slope of the fault Rift Valley: When two normal faults occur parallel to each other, with the plate in-between dropping down as the plates move away from each other.

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Block Mountains - The land between two parallel faults that have sunken, the block of rock could have risen, or both scenarios. Reverse Fault A fault, perhaps caused by a compressional force, where movement is up, rather than down, the face over which movement occurs Overthrust Fault - A fault that has previously undergone folding, with one set of rock layers pushed up and thrust over other rock layers. Mountains Formed by Volcanoes

· Along plate boundaries, heat is generated because of friction, pressure, and decay of radioactive materials.

· Intense heat melts rock beneath the crust producing magma · If it reaches the surface through fractures or vents, extrusive volcanic

activity takes place.

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Terms: Lava - liquid rock Ash (cinder) - small molten rock fragments Vent - Single opening through which the volcanic products erupt Mild volcanic eruptions

· thin, liquid lava flows · small amounts of gas

Explosive volcanic eruptions

· thick lava flows · large quantities of gas, ash and cinders

Why do volcanoes erupt?

- It is driven by buoyancy and gas pressure - Molten rock, which is lighter than the surrounding solid rock, forces its

way upward and may ultimately break through zones of weaknesses in the Earth's crust.

- If so, an eruption begins: The molten rock may pour from the vent as non-explosive lava flows…

- Or if may shoot violently into the air as dense clouds of lava fragments. - Molten rock below the surface of the Earth that rises in volcanic vents is

known as magma. - After it erupts from a volcano it is called lava. - The explosive quality of the volcano is directly related to the thickness of

the the lava. This lava does not flow easily out of some openings, tending to solidify and plug the opening.

- Pressure builds and as a result trapped material explodes through the passageway.

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Three types of Volcanic Cones:

Ash and Cinder Cone

· eruptions consist mainly of ash and cinders · thick, slow flowing, rapidly solidifying lava · shape is symmetrical · steep sides · large crater

Shield Cone

· usually milder eruption · little or no ash and cinders · very thin, liquid lavas · broad, flat cones

Composite Cone

· undergoes periods of both explosive and quiet activity.

· layers of ash and cinders intermixed with layers of lava.

· weak spots may develop on sides with smaller lava flows forming smaller craters.

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Chapter 2 - Wearing Down Landforms: Rivers and Ice Weathering vs. Erosion

· Weathering is the breakdown of rock and minerals.

· Erosion is a twofold process that starts with 1) breakdown of land (weathering) and also includes the movement (transportation) of these weathered materials 2) Deposition of the eroded material occurs when it is dropped in a new location.

· Denudation is a term that refers to the wearing down or smoothing off of land features. The processes of weathering and erosion are denudational . They are also gradational because they grade the earth’s surface.

Physical Weathering vs. Chemical Weathering

· Physical weathering is the breakdown of rock and minerals by mechanical stress

· Chemical weathering breaks down rock with chemical reactions often including water.

Types of Physical Weathering

· Frost fracture – the expansion of freezing water that causes rocks to crack.

· Heat expansion – rocks can expand and subsequently fracture.

· Plant growth – expansion due to root growth.

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· Burrowing animals- tunneling animals can increase the size of existing cracks

· Exfoliation – as internal pressure is released from certain rocks, it can

cause layers to split and fall off. Environment’s Affect on Physical Weathering

· Fast temperature changes like those that occur in the desert, increases the amount of physical weathering due to heat expansion. Conversely, in regions like the tropics where there is little temperature change, the amount of physical weathering due to heat expansion is minimal.

· Abundant precipitation combined with alternating freezing/thawing

temperatures increases the amount of frost fracture. Conversely, the absence of those climatic conditions reduces the amount of frost fracture.

· Running water increases physical erosion as friction occurs between

water and rock. · Ocean waves cause hydraulic pressure and abrasion on the shore

leading to physical weathering. Types of Chemical Weathering Chemical weathering is the breakdown of rocks and minerals by chemical reactions and usually involves the action of rainwater. There are three different types of chemical weathering described below: · The formation of solutions as rainwater absorbs CO2 , SO2, and other

chemicals from the atmosphere along with organic acids from the soil, which then reacts with rock and minerals causing some to dissolve and move away.

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· Hydrolysis, like the first process, involves the minerals in solution. In this case, carbonic acid reacts with silicates in some rocks leaving a soft clay from which potassium, sodium and magnesium are subsequently leached.

· Oxidation is the reaction of metallic minerals to oxygen (mainly in water). This results in the formation of oxides, which tend to be softer than the original mineral. For example, rust on iron.

How Environmental Conditions Affect Chemical Weathering · Heavy rain, running water, and abundance of water increases the

amount of dissolving that occurs. Conversely less abundance of water leads to less dissolving.

· High temperatures will increase the rate of chemical reactions. It is a fact of chemistry that heat increases the speed of many reactions like oxidation.

· Ocean water contains salt which can increase the rate of many reactions like oxidation.

Life Cycle of a River Rivers change over time and seem to go through three stages:

· Youth · Maturity/Late Maturity · Old Age

Youth (figure 2.7 p.28)

· Are usually found in highland or mountain regions. · They tend to have a steep slope (high gradient) · Usually have a small volume of water · They have a rapid flow of water · There is usually very rapid erosion especially vertically · A narrow ““V”” shaped valley is characteristic

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· Water falls and rapids are common Maturity (figure 2.7 p.28)

· Most high relief is eroded · Gentler slope · Many well developed tributaries · Broad flat river valley · Well developed floodplain · More lateral erosion than vertical · Meandering results

Late Maturity (figure 2.7 p.28)

· Remember the stages are not distinct. · These changes occur over long periods of time.

Old Age (figure 2.7 p.28)

· Almost no slope · Very little relief · Elaborate meandering · Oxbow lakes develop · Often swampy areas around river · Very muddy due to slow speed · Most susceptible to flooding because of large floodplain.

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Evaluating Evidence to Determine the Age of Rivers There are six common pieces of evidence you can look for to determine the stage of a river:

· Slope of the river (steeper = younger) · Relief of the banks (steeper = younger) · Width of the valley (wider = older) · Meandering (more = older) · Size of floodplain (wider = older) · Rapids or waterfalls (more = younger)

Two Directions of River Erosion: Vertical erosion makes rivers deeper as is the case in young rivers Lateral erosion makes rivers wider leading to the meandering of mature rivers. Drainage Basin is the area of land drained by a river and its tributaries. River Deltas

· A delta is a low lying area at the mouth of a river formed by deposition of silt. Deposition occurs because a river slows as it enters an ocean or lake.

There are three types:

· arcuate · digitate · estuarine.

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Arcuate Delta:

· named from the Latin word for curved in the shape of a bow.

· Fan shaped · ex. Nile Delta ( p. 32)

Digitate Delta:

· From Latin for finger · Delta with long fingers of sediment

reaching into the sea · ex. Mississippi Delta ( p. 32)

Estuarine Delta:

· Formed when rivers run into a bay or estuary

· Tidal mudflats form and can be seen at low tide

· Sediment deposited from river outflow and from Tidal inflow

· The Seine River Delta (figure 2.12 on p. 32)

· To the right is a satellite photo of the Amazon Delta, notice the tidal flats or islands that cover and uncover with the tide.

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Continental Glaciers vs. Alpine Glaciers Continental Glaciers cover parts of continental land masses like Greenland

· a mass of ice, situated over most of a continent, which may be moving, or has moved, overland.

Alpine Glaciers are found high in mountain valleys, above the snow-line

· a mass of ice, situated on an upland, which may be moving, or has moved, overland.

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Differences: · Location - Alpine glaciers are only found on mountain tops

whereas continental glaciers are only found at the earth's poles regardless of elevation.

· Size - Alpine glaciers are smaller compared to Continental glaciers.

Similarities:

· Both move and cause erosion. · Both change the landscape. · Both developed in constantly cold temperatures below freezing.

Continental Glaciers

Outwash plain:

· Like a river Delta · Melt water flowing from glacier deposits silt like river deltas · Silt is deposited in layers · Small particles are carried further away · Larger particles drop closer to the glacier

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Terminal Moraine: · Heap or ridge of bulldozed gravel that marks the end of the

forward motion of a glacier. · As a glacier retreats it deposits debris/gravel

Erratics:

· Large boulders that were transported long distances and dropped.

· They now sit in a region and look very much out-of-place. Drumlins:

· Egg shaped hill · Formed under glaciers · Sloped or Pointy end points in direction of ice flow

Formation: · Ice melts under glacier · Deposits of gravel are made · Glacier moves forward · Deposits are bulldozed along and catches up in

rough areas forming piles or drumlins. Eskers:

· Long deposits of eroded glacial material · Formed by subglacial streams that deposit material like all

rivers. · They are sometimes known as Highways of the North because

they are good for traveling on with ATV's.

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Evidence for Direction of Glacier Movement

· The gently sloped end of drumlins point in the direction of glacier movement.

· The terminal moraine marks the furthest extent of the glacier. · The layers of silt in an outwash plain can indicate direction of

glacier movement. Fine particles would be at the leading edge while larger particles would have been closer to the glacier.

Alpine Glaciers

Alpine glaciers are like very slow moving rivers of ice flowing down high mountain valleys.

· create land forms by weathering and deposition · typically erode the mountain beneath them into a U-shaped

valley with steep sides · Some alpine or valley glaciers are 1000m thick and up to 160

km long, though most are only a few km in length

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Cirque · a circular hollow cut into bedrock during glaciation · Side and back walls are steep but front wall opens downward

Cirque Formation

· Alpine glacier freezes onto mountain valley and as is proceeds it plucks/gouges rock from the mountain top leaving the cirque shape.

Arête

· Steep knife edged ridge between two cirques in a mountainous region.

Hanging Valley

· A high level tributary valley from which the ground falls sharply to the level of the lower, main valley. The depth of the lower valley is due to more severe glaciation.

Lateral Moraines

· a landform deposited by a glacier or ice sheet at the side of the glacier.

Terminal Moraines

· deposits that mark the farthest extent of the alpine glacier the same as with continental glaciers.

Fjords

· Alpine Glaciers erode troughs and valleys in the mountain · Glacier valley reaches the coast. · Glacier melts and sea water floods the valley · Fjords are very common in Norway and a quick search on web

can find you some amazing pictures.

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Chapter 3 - Wearing Down Landforms: Wind and Waves Wind Erosion

· not usually very strong · tends to just pick up and transport sand and fine sediment,

wearing down Deflation

· the action of the wind in removing material from a surface and lowering that surface.

· most effective where extensive areas of non-cohesive deposits are exposed (ie. Loess or dry lake beds)

Abrasion

· the grinding away of bedrock by fragments of rock incorporated in ice, water, or wind

Wind Deposition

· If wind takes away sand and particles - must deposit them somewhere.

5 Formations of Wind Deposition/Erosion:

1. Hamada · level, rocky desert that has been smoothed by abrasion · northern Africa · an example of deflated landscape - landscape in which the

wind has blown away all fine, loose material - appears as deserts of jagged rocks or pebbles

2. Erg · arid, sandy desert · consists of extensive dunes, mounds and ridges of sand

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· Great Erg - Sahara Desert - area of Atlantic Provinces - mounds of sand 1200 m thick

3. Sand Dunes · a hill or ridge of sand sorted and accumulated by wind action · crescent or triangle shaped piles of sand deposited when the

wind slows down or stops blowing · shape depends on amount of sand available, the speed and

duration of the wind, the wind’s direction, and the amount of vegetation in the area

4. Barchan · a sand dune formed with the

horns pointing downwind · crescent shaped – migrate

5. Loess · any unconsolidated, non-stratified soil composed primarily of

silt-sized particles · moved by winds can be carried thousands of miles - across

continents, oceans etc. · sometimes very fertile soil.

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Terms Related to Water/ Wave Erosion Three processes by which wave action erodes coastal areas:

1. Hydraulic pressure = The pounding force of water/waves 2. Corrosion = Minerals such as calcium carbonate and limestone

dissolve in the water 3. Abrasion = rock and sand particles suspended in the water

bump, grind, scrape and gouge surfaces the water hits. Refer to diagrams in handout. Longshore drift terms

1. Headlands = the protrusions of land that extend the farthest out into wave action.

2. Longshore drift = refers to the fact that dominant waves have

enough energy to carry silt/sand from headlands along the shore where it is later deposited.

3. Wave Refraction = waves bending around headlands as they

hit the shallow water by shore

4. Spit = A ridge of sand running away from the coast, with a curved seaward end. Spit grows in the prevailing direction of longshore drift. Ends are curved by the action of waves in different directions.

5. Bay Bar = A ridge of mud sand or silt extending across a bay. Formed when spits stretch across the mouth of the bay.

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6. Bay Beach = An accumulation of sediment deposited by

waves and longshore drift along the shore of a bay. Straightening of an Irregular Submerging Coastline

· Irregular submerging coastlines have headlands that protrude out from the shore line.

· The erosion of the headland can deposit silt in the bay which forms a bay beach as it tends to reduce the irregularity of the coastline. The headland is reduced due to erosion and the bay is being filled by deposition.

· Longshore drift results in some sand being deposited parallel to

the shore but connected to the headland. These silt deposits are known as spits.

· Longshore drift and deposition can continue to the point that the spit closes off the mouth of the bay. This extensive deposit is known as a bay bar. As you can see it tremendously reduces the irregularity in the coastline.

· Continued erosion and deposition can straighten a coastline over a long period of time.

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Erosion of Emerging Coastlines The Evolution of Sea Stacks

· Sea stacks are columns of land standing in the ocean just off shore.

· They are created over a long period of time after a series of other land structures have eroded away.

· First sea caves are formed in a headland. Continued erosion turns sea caves in to the second land feature, sea arches. Sea stacks are common in eastern Canada.

· Many have plant growth on top.

· Sea arches are an interesting sight too and have drawn many

tourists to the northern Peninsula of Newfoundland.

· Erosion and eventual collapse of the arch top leaves a sea stack standing in the ocean. Figure 3.11 on pages 48-49 shows this evolution from three different points of reference.

· You must look at this figure; it will help cement the concepts in your mind.

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Sea Cave Formation: "a" in figure 3.11 on page 48 ● Waves strike the headland first. ● Waves refract around the headland and put hydraulic pressure

on both sides of the headland. ● Erosion of the weak portions create caves and blow holes in

the sides of the headland. Sea Arch Formation : "b" in figure 3.11 on page 48

● Eventually sea caves, on alternate sides of the headland get deeper until they connect inside the headland forming a complete passage way or tunnel or “arch” through the head land.

Sea Stack Formation: "c" in figure 3.11 on page 48

● Continuous erosion, of sea arches, causes the collapse of the ground over the arch.

● This leaves a pillar or column or “STACK” of land standing alone where the headland was.

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Straightening of Emerging Coastlines

▪ Emerging coastlines straighten in much the same fashion as submerging coastlines.

▪ Erosion of headlands creates sea caves, sea arches and sea stacks instead of bay beaches, spits and bay bars.

▪ However the result is similar in that headlands are reduced in size which straightens the coastline. Compare the headland length in figure 3.11 before and after erosion.