Earth and Space€¦ · •Wind •Glaciers •Surface Water •Ground Water . Mass (Ground)...

Earth and Space

Introduction

How do landforms (like mountains, hills, and plateaus)

change?

Introduction Mass movement includes:

• Ground (Earth)

• Wind

• Glaciers

• Surface Water

• Ground Water

Mass (Ground) Movement

Mass Movement • Landforms can change through processes

involving: – Water

– Wind

– Ice

– Gravity

• Mass Movement – the downslope movement of soil and weathered rock resulting from the force of gravity

Mass (Ground) Movement Mass Movement • Remember, weathering processes weaken

and break rock into smaller pieces making it easier for gravity and other processes to transport it in mass form

• Climate has a big swing on these processes – Different weather conditions cause different types

and amounts of weathering for a given area • Ex: Areas that get a lot of rainfall in just one season

would see a possibility of mass movement just during that time frame or shortly after


Mass Movement • Because few places are completely flat, most

movements occur where there are slopes, even really small ones

• Some are barely detectable, while others can be catastrophic and sudden slides, falls, and flows

• The material that gets moved can be simple, fine-grained rock up to giant boulders

Mass (Ground) Movement 4 Factors that Influence Mass Movement • Material’s weight

– Works to pull the material downslope with gravity

• Material’s resistance to sliding or flowing – Depends on the amount of friction, how cohesive the

substance is, and whether it is anchored to the bedrock or not

• A trigger – Ex: earthquake, shakes the material loose

• Water – Landslides can happen after heavy rains making the

soil heavy


Types of Mass Movements

• Creep – slow, steady, downhill flow of loose, weathered Earth materials – Mainly soils

– Little as a few cm a year

– Noticeable over long periods of time

– How do you tell? Watch the change in position for structures and other objects

– Loose materials on slopes almost always creep, even if it’s just a little bit


Types of Mass Movements

• Creep – slow, steady, downhill flow of loose, weathered Earth materials – Usually occur in areas of permafrost

(permanently frozen soil)

– The water that thaws from the frozen mud creeps down and then refreezes • This is called solifluction

Mass (Ground) Movement Types of Mass Movements • Flows – flowing material as if it was a thick

liquid – Can move as slow as a couple cm a year or as rapid

as 100 km an hour! – Earth flows are usually slower flows – Mud flows are usually much faster and made up of

mud and water • Can be triggered easily by earthquakes or similar vibrations

around volcanoes where the heat melts the snow and the soil is supersaturated

• The water fills the fine spaces in between the grains allowing it to slip and flow really easily!


Types of Mass Movements • Volcanic mudflow

Mass (Ground) Movement Types of Mass Movements • Lahar – type of mudflow

that occurs after a volcanic eruption – Product of a snow covered

volcanic mountain erupts and melts the snow on top

– That melted snow mixes with the ash and flows downslope

– These can travel over 100 km and cause major destruction!


Types of Mass Movements • Mudflows

– Common in sloped, semi-arid regions that experience intense, short-lived rain storms

– Areas that have forest fires have little vegetation to hold the ground in place when it rains

– Ex: Los Angeles


Types of Mass Movements • Landslide – a rapid, downslope movement of

Earth materials that occurs when a relatively thick block of soil, rock, and debris separate from the underlying bedrock – Eventually stops and becomes a pile of debris with

little internal mixing

– Common on steep slopes

– Rockslides are some of the most common and usually triggered by earthquakes


Types of Mass Movements • Slump – when a mass of material in a landslip

moves along a curved surface – The material on top moves inward and exposes

the bottom material causing it to move outward

– Common in areas with thick soils

– Can also be triggered by earthquakes

– Leaves crescent shaped scars on slopes


Types of Mass Movements • Avalanches – landslides that occur in

mountainous areas with thick accumulations of snow – Radiation from the sun melts the surface of the

snow which refreezes at night into an icy crust

– This crust gets snow accumulated on top of it, making it heavy, and with it being ice (little friction) it gives way

– Occur on slopes between 30 and 45 degrees


Types of Mass Movements • Rock Falls – when large rocks or boulders are

knocked loose by physical weathering and fall directly downward – Can roll and tumble downward

– Usually held in by vegetation

– Common in areas where roads were cut out and rocky shorelines

Wind Wind Erosion and Transport

• A current of rapidly moving air (wind) can pick up and carry sediment in the same way that water does

• Outside of natural disasters, basic winds can’t usually carry particles the size of ones water can move – Water is more dense, making it more powerful

when moving at the same speed as a wind current


• Wind is a great contributor to erosion

• Wind can move particles by: – Creep - causes particles to roll

– Suspension –strong winds cause small particles to stay airborne for long distances

– Saltation – causes larger particles to bounce along (rather than roll)

Wind Wind Erosion and Transport • Limited precipitation means little water to help

hold particles of sediment together • Limited precipitation also means little vegetation

that also helps hold the particles of sediment together

• Wind erosion is common in areas that are considered: – Deserts – Semiarid areas – Seashores – Some lakeshores


• Pg. 201

Wind Deflation

• Deflation – the lowering of the land surface that results from the wind’s removal of surface particles – This is what caused the Dust Bowl in the 1930s

– The Great Plains had a severe drought and little vegetation so the wind currents moved the soil particles around

– The Plains now have deflations blowouts where shallow depressions can be found at the surface

Wind Deflation

• Deflations can range from a few meters to hundreds of meters in diameter

• Found in areas that have sandy soil – easy particles to move

• Desert Pavement – when strong wind erosion carries away all of the fine soil particles and all that are left behind are the gravel and pebble particles

Wind Abrasion • Abrasion – when particles (like sand) rub

against the surface of rocks or other materials • Occurs as part of the erosional process with/in:

– Winds – Streams – Glaciers

• Because the sand that gets blown around by wind is usually quartz, it’s tough stuff – This really helps the erosion process when it hits

into those other rocks

Wind Abrasion • Things that can be damaged by wind abrasion:

– Telephone poles – Paint on outdoor structures – Windows – Vehicles – Trees and other larger plants

• At first, these objects end up becoming pitted and grooved

• After a while, abrasion polishes the objects and smoothens their surfaces

Wind Abrasion

• Ventifacts – rocks that have been shaped by windblown sediments

• These can range in size from pebbles to boulders

Wind Wind Deposition

• Occurs in areas where wind velocity decreases

• Once the wind slows down, the particles can’t stay airborne and end up falling to the ground

• These particles tend to accumulate where there is: – A large rock

– Landform

– Piece of vegetation • These all block the forward motion of the particles


• Dune – pile of particle build up from the wind blowing and depositing it in one direction

• The gentler slope of the dune is located on the windward side

• The sharper slope of the dune is located on the under (or protected) side called the leeward side


• Conditions for dunes: – Availability of sand

– Wind velocity

– Wind direction

– Amount of vegetation present

• All of these conditions can change the shape of the dune(s)

Wind Dune Migration

• As long as the wind continues to move in one direction, the dunes it creates will migrate

• Caused when prevailing winds continue to move sand from the windward side of a dune to the leeward side

• Moves slowly over time

Wind Dune Migration

• Barchan Dunes – Form solitary, crescent shapes

– From small amounts of sand

– Covered by minimal or no vegetation

– Forms in flat areas with consistent wind direction

– Crests point downwind

– Max size for the dunes: 30 m

Wind Dune Migration

• Transverse Dunes – Form series of ridge shapes

– Form from a large amount of sand

– Covered by minimal or no vegetation

– Form in ridges that are perpendicular to the direction of the strong wind

– Reach max size of 25 m

Wind Dune Migration

• Parabolic Dunes – Form u-shapes

– From a large amount of sand

– Covered by minimal vegetation

– Form in humid areas with moderate winds

– Crests point upwind

– Max size is 30 m

Wind Dune Migration

• Longitudinal Dunes – Series of ridge shapes

– From small or large amounts of sand

– Covered by minimal to no vegetation

– Form parallel to variable wind direction

– Max height is 300 m

Wind Loess

• Silt and clay can get carried for a long time over really long distances

• Many parts of Earth’s surface are covered by thick layers of yellow-brown windblown silt

• Accumulates over 1000s of years

• Loess- thick, windblown silt deposits – Some of the most fertile soils because they contain

an abundance of minerals and nutrients

Wind Loess

• Pg. 206

Glaciers Moving Masses of Ice • Glacier – large mass of moving ice

– Form near Earth’s poles and in mountainous areas at high elevations

– Cover about 10% of Earth’s surface – Last ice age was about 1.6 mya and ended more

than 10,000 – Accumulated snow in areas that are around 0˚C

year round turn to glaciers (i.e. – Greenland) – 2 types:

• Valley • Continental

Glaciers Valley Glaciers • Valley Glacier – glacier that forms in valleys in

high, mountainous areas – Movement of these guys occurs when the growing ice

mass becomes so heavy that the ice maintains its rigid shape and begins to flow

– Flow begins when snow and ice accumulate and gets to be above 40 m in thickness

– Speed of the glacier is affected by the slope its on, temperature/thickness of the ice, shape of the valley walls

– Moves slow (less than a few mm a day) – Carve out the valley as they move

Glaciers Continental Glaciers

• Continental Glaciers – glaciers that cover broad, continent sized areas – Form in cold climates where snow accumulates

over many years

– Thickest at the center

– Currently, Greenland and Antarctica have these

Glaciers Glacial Movement • Both valley and continental glaciers move

outward when snow gathers at the zone of accumulation

• Zone of Accumulation – a location in which more snow falls than melts, evaporates, or sublimates (solid directly to gas) – Center of the ice sheet

• both types of glaciers recede when the ends melt faster than the zone of accumulation builds up snow and ice

Glaciers Glacial Erosion

• Most powerful with erosion – Due to size, weight, and density

• When they move, they break off rock and dig into the surface causing striations (small scratches in the surface) and grooves (large divots in the surface)


• Cirques – deep, bowl-shaped depressions carved out by valley glaciers

• Horn – when valley glaciers are on 3 or more sides of a mountain and carve it into a steep, pyramid


• Hanging Valleys – formed when higher tributary glaciers converge with the lower primary glaciers and later retreat – The lower glacier meets the height of the primary

and they join

– Once they melt, they leave a giant waterfall that drops down into a river

Glaciers Glacial Deposition

• Moraines – glacier deposit ridges of till (unsorted rock, gravel, sand, and clay) – Terminal moraines are found along the edge

where the retreating glacier melts

– Lateral moraines are found parallel to the edge of the retreating glacier melts

Glaciers Outwash

• Outwash Plain – area at the leading edge of the glacier where the meltwater flows and deposits outwash (sediment carried by the water melted from the glacier)

Glaciers Drumlines, Eskers, Kames

Glaciers Glacial Lakes

• Kettles – glacier lakes that form when melted water fills kettle depressions formed when the glacier recedes

Surface Water Introduction

• Water follows its own cycle – It gets evaporated

– The water vapor condenses

– It precipitates to the ground

• Once it precipitates, it can: – Infiltrate the ground (groundwater)

– Runoff the side of a land formation or structure

Surface Water Runoff

• Runoff – water flowing downslope along Earth’s surface – Might:

• Reach a stream, river, lake

• Evaporate

• Accumulate in puddles

– For water to infiltrate the ground: • There must be large enough pores or spaces in the soil

and rock to accommodate the water’s volume

• If the pores are already full with water, the remaining precipitation will result in runoff

Surface Water Runoff

• There needs to be a slope for there to be run off – If there is no slope, the water will puddle on a

surface

– Cohesion and adhesion hold it together

• Water on the surface eventually: – Evaporates

– Flows away

– Slowly enters the groundwater

Surface Water Soil Composition

• The physical and chemical composition of soil affects its water-holding capacity

• Soil contains: – Minerals

• Grain particles labeled as: sand, silt, and clay – Sand: large particles and therefore large pores

– Silt and clay: small particles and fewer/smaller pores

– Decayed organic matter called humus • Creates pores in the soil and increases the soil’s ability to

retain water

Surface Water Rate of Precipitation

• Light and gentle precipitation can infiltrate dry ground – Better for plants

• When the rate of precipitation exceeds the rate of infiltration, runoff is produced – Can cause erosion

Surface Water Vegetation

• Vegetation helps with infiltration – Plant roots help with pores in the ground

• Runoff is much more common in areas with little to no vegetation – Without the root systems, the soil clumps together

and prevents the water from seeping through

Surface Water Slope

• The slope of a land area plays a significant role in determining the ability of water to enter the ground – A more gentle slope allows water to

infiltrate the ground than a steeper one

– The steeper the slope, the faster the water moves, the least likely it will seep into the ground

Surface Water Stream Systems

• Some surface water flows in thin sheets and eventually collects in small channels – These are areas where streams flow

• As the amount of runoff increases, the channels: – Widen

– Become deeper

– Become longer

Surface Water Tributaries

• All streams flow downslope to lower elevations

• The path of the stream can vary depending on: – The slope

– The type of material in the channel

• Some streams flow into lakes, while others right into oceans

Surface Water Watersheds and Divides

• Watershed – all of the land area whose water drains into a stream system – Can be small or really large

• Divide – elevated land area that separates one watershed from another

Surface Water Watersheds and Divides

Surface Water Stream Load

• Suspension – is the method of transport for all particles small enough to be help up by the turbulence of a stream’s moving water – Ex: silt, clay, and sand

– Based on volume and velocity of the stream

– Faster water = more suspended

• Bed Load – consists of sand, pebbles, and cobbles that the stream’s water can roll or push along the bed of the stream

Surface Water Stream’s Carrying Capacity • Carrying Capacity - the ability of a stream to

transport material – Depends on the amount of water and the water

velocity – Water moves more quickly in areas with less friction

• Discharge – measure of the volume of stream water that flows past a particular location within a given period of time – m3/s unit – The Mississippi River has a very large average of

17,000 m3/s

Surface Water Floods

• Flood – occurs when water spills over the sides of a stream’s banks onto the adjacent land

• Floodplain – broad, flat area that extends out from a stream’s bank and is covered by excess water during times of flooding – Area where all of the flood waters drop their

sediments and leave them behind and they recede and evaporate

– Because of the sediment, these soils are very fertile and great for farming!

Groundwater The Hydrosphere

• 97% of the hydrosphere is ocean (marine) water

• 3% is freshwater (mostly frozen) – Less than 1% is liquid freshwater

• Groundwater is .31% of the liquid freshwater on the planet

Groundwater Groundwater and Precipitation

• Infiltration – process by which precipitation that has fallen on land trickles into the ground and becomes ground water – Water that isn’t absorbed is labeled as runoff and

is transported to the oceans (eventually)

– Eventually even the groundwater will make it back to the oceans by being exposed to steams through springs, wells, and other water sources

Groundwater Groundwater Storage

• When puddles are found on the surface, some of the water can infiltrate if the water doesn’t evaporate quickly

• Pores – spaces within soil that allow water to pass through – The greater the porosity, the more water can be

stored in the material

– Can range from 2% to more than 50% • Well sorted sand = 30%

Groundwater Zone of Saturation

• Zone of Saturation – the region below the Earth’s surface where groundwater completely fills all of the pores in a material – Water Table – upper boundary of the zone of

saturation

– Zone of Aeration – area above the water table where materials are moist, but because it’s not completely saturated with water, there are air pockets in there


• The depth of the water table varies depending on local conditions – In valleys: the water table is pretty close to the

surface

– In swampy areas: the water table is at the surface

– In arid regions: the water table is tens to hundreds of meters below the surface

Groundwater Groundwater Movement

• Permeability – the ability of a material to let water pass through it – Large pores = high permeability

– Small or few pores = low permeability

• Impermeable materials: clay, silt, shale

• Permeable materials: fractured bedrock, sandstone, and limestone


• Aquifers – permeable sediment and rock – The pore spaces are large enough and connected

to be able to hold water

• Aquicludes – impermeable layers that act as barriers to the groundwater flow


• The flow velocity of groundwater depends on: – Slope

– Permeability of the material through which the groundwater is moving

Groundwater Springs

• Springs – natural discharge of water from the ground table to the Earth’s surface – Common in areas with high slopes

• This depends on the location of the aquifers and aquicludes under the ground

– The volume of water can be: • equivalent to a stream

• only a mere trickle

• can be obsolete during parts of the year

Earth and Space€¦ · •Wind •Glaciers •Surface Water •Ground Water . Mass (Ground)...

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Transcript of Earth and Space€¦ · •Wind •Glaciers •Surface Water •Ground Water . Mass (Ground)...