2.3.2 - The Lithosphere (KQ3): Causes of Mass Movement

Causes of Mass Movement

So, we have alluded to the reasons masses move down slopes, but here we will discuss them in more detail.  

Please view Tulane Univeristy Prof. Stephen A. Nelson's unit on Mass Wasting Processes here.  In the website, find the following processes required by Cambridge, and make sure you know them.  The diagrams within help visualize the information.  Take Notes...it's good for ya!

• Flows and Slides (Including Rock Flows)
• Landslides
• Earth Slumps/Rotational Slumping
• Soil Creep
• Soilfluction
• Mudflows

2.3.4 - The Lithosphere (KQ3): Slope Management Policies

Slope Management Policies

OK...so we have these mass movement issues...how should we best manage them?  There are 4 main techniques that you will discover here:  slope angle reduction, afforestation, drainage, and surface protection. 

Slope Angle Reduction

If it is determined that an area is going to be prone to landslides due to a steep slope, soil can be moved in to reduce the grade (angle) to try and prevent the likelihood of mass movements along them.  If an area has been cut away, bringing in land to fill the void may also take much of the risk of mass movement away.

Afforestation

Afforestation is planting trees and vegetation in areas where currently none grows.  For the purposes of mass movements, this is done to stabilize the land by providing leaf litter and root structure.  Reforestation is the process of reclaiming a land to it original state, one it is found that be deforesting, it is susceptible to mass movements.  Replanting trees can increase drainage into the ground and prevent water from eroding the soil away.  Also, trees provide transpiration, which is how they soak up the water and evaporate it back in the air.

Drainage

Areas in which it is determined landslides may occur may set up drainage systems to divert water away from slopes and into established waterways.  This can be done by making troughs in the land that diver the water away or with pipes that bring the water around the areas in danger.

Surface Protection

Areas may be covered with vegetation or other natural material (like mulch) in order to protect it from flowing water or air.  This may be the easiest measure to protect against mass movement, but bring with it the obvious hurdle that it must be replenished at certain intervals if the material is just sitting on the ground, rather than planted in it.

Just a thought...Ask yourselves, without human interference, would all of these policies be necessary?  Or are we just cleaning up our own mess?

2.3.3 - The Lithosphere (KQ3): Human Influences & The Causes of Sudden Mass Movements

Human Influences

Mostly, from what we have studied about mass movements so far, you probably are only thinking in terms of naturally occurring mass movements.  However, there are anthropogenic (human) activities that have a large effect on long-term mass movements as well.  The two of main concern for us are deforestation and building.

Deforestation is the removal of plants and trees from a large area so that it can be used for human activity.  The human activity can be defined as anything that is not the natural use for the area.  One of the kind-of non-obvious forms of deforestation is the conversion of natural land to farm/grazing land.  While this is the first time deforestation is a topic in this course, it will not be the last.  It has detrimental effects in all 4 spheres and is one of the human activities that has the worst consequences.

To understand how deforestation effects mass movements, we first must understand the importance of vegetation to soil.  If a forest is undisturbed, very little soil moves or is lost from the area.  The leaf litter (fallings that sit on the ground) protect the soil from erosion.  If the trees and vegetation are removed and replaced with something else, the leaf litter can not accumulate, and thus the soil is susceptible to water running it off or wind erosion.  Soil without vegetation will not absorb water well either, so the rate of runn-of will increase.  The root structure of trees also stabilize the soil underneath the ground cover, so their removal leaves the soil loose and more likely to erode.  If the soil is loose, not only is is susceptible to erosion, if it is on a slope, it can cause landslides.

Check out this picture from Chile showing an area before and after deforestation.  You can see how the loss of vegetation can leave the area wide open to destruction.

Building structures on land and the clearing of that land can have the same effects as deforestation.  Another major problem is that land is moved to different places, and usually that soil is loose where it moves, and thus susceptible to erosion.  Buildings also take away natural drainage systems and then cause the water to move over places it normally wouldn't, which could cause erosion in those parts or flooding.

Causes of Sudden Mass Movements

Sudden, unexpected mass movement of land (ex. landslides) can be the result of natural phenomena or due to human interference.  The following will give you a short overview of some events in both categories.

Natural

• Massive intense and/or prolonged rainfall - can loosen up the soil, and create heavier flowing soil
• Earthquake - simple enough...earth shakes, soil becomes loos, flows down a slope.  Also can cause liquefaction, where the pores in soil are compacted by the seismic vibrations from an earthquake, causing deformation of the land, possible breakage and flow.
• Volcanic activity - pretty much the same as with earthquakes...the seismic activity can trigger movement of land.  Also, the vents and features associated with a volcano will be weak following the eruption, may collapse, and take land with them.
• Snowmelt - If there is a sudden increase in temperature in a mountainous region with heavy snow, the snow will melt, causing a mass movement of water, which may result in landslides.
• Rapid falling levels of groundwater or surface water - The water level adjacent or below an area of land may be susceptible to rapid decline after a flood or during a particularly high-temperature event.  The water level acts as a barrier to a slope, and without it, the soil may give way to a landslide.

Human Caused

• Excavation - as humans excavate land, they inherently destroy the structure that it established for that area.  This can leave an area more in danger of the natural events described above causing landslides than if the area was left alone.
• Mining - Digging into the earth to get some of the valuable materials can leave the earth scarred...and filled with more empty space.  Empty space may collapse, and thus, trigger mass movement.
• Vibration - Many human processes cause vibration of the land (think of a jackhammer).  Think of this as a "human earthquake" - can destabilize the land in the same way and cause liquefaction.
• Drawdown - When water is drawn down from a water body, the same effect as the groundwater or surface water natural cause may occur.
• Explosions - We use explosions for many things...from mining to fracking (getting natural gas from the ground), explosions have their use...and are pretty awesome!  However, if the land is not stable enough, explosions can trigger mass movements by being the "spark" that causes the movement.
• Deforestation/Land Use Change - As shown above, deforestation or changing the use of a land can cause slow mass movement.  It can also leave the are much more prone to sudden mass movement, as the soils are loose and not covered.

2.3.1 - The Lithosphere (KQ3): Weathering and Accumulation of Debris on Slopes

Rock Weathering and the Accumulation of Debris on Slopes

KQ3 focuses on mass-movements on slopes (ex. landslides).  These can be devastating and are sometimes preventable where human tragedy is concerned.  We will be looking at the processes behind the mass-movements, how we can manage the land to prevent them affecting us, and how we can best respond.

Rock Weathering

We already had a basic introduction to rock weathering in our rock cycle unit here.  It is important to revisit and expand on this topic, because in order to truly understand how to deal with a problem, we need to know how and why it occurs.  We're going to do this with a little help from this site.  Many of the weathering ideas presented here are influenced from the information there, but there is more information there than you need at this point, so I will summarize below.

Weathering  is a process which acts at the earth's surface to decompose and break down rocks.

There are 2 types of weathering we are mainly concerned with:  Mechanical (Physical) and Chemical

Mechanical Weathering:  Basically, breaking down rock from bigger to smaller pieces without changing the composition.

There are 4 basic types of mechanical weathering:

1. Expansion and Contraction - the thermal heating and cooling of rocks causing expansion and
   
   contraction.
2. Frost Action - Water freezes at night and expands because the solid occupies greater volume. Action wedges the rocks apart. Requires adequate supply of moisture; moisture must be able to enter rock or soil; and temperature must move back and forth over freezing point.  WARNING...the following is a graphic!!!
3. Exfoliation - process in which curved plates of rock are stripped from a larger rock mass.
4. Other types - Cracking of rocks by plant roots and burrowing animals.

Chemical Weathering:  Breakdown of rocks by chemical processes/reactions.  Water is the main agent, carrying dissolved chemicals (including acids) that react with the rocks and deteriorate them.  The major acid that is responsible for chemical weathering is carbonic acid...which is produced with carbon dioxide dissolves in water.  The carbonic acid will break down rock into smaller pieces...and smaller pieces are much more unstable.

The Factors which effect the rate of chemical weathering are:

• Particle size - Smaller the particle size the greater the surface area and hence the more rapid the weathering
• Composition
• Climate (See Figure)
• Type and amount of vegetation

As you can see, with differing average annual temperature and rainfall amounts, the types of rock weathering change per region. The dryer and colder areas seem to have more mechanical weathering (think...frost action), while the wetter, hotter areas get more water, and therefore more carbonic acid, causing an increase in chemical weathering.

Accumulation of Debris on Slopes

Mechanical and Chemical weathering can both result in the accumulation of rocks on a slope.  The rock is broken down by the weathering processes and then will roll down a slope.  The terms used for this rock are talus or scree (they mean the same thing).  The accumulated rock are sometimes called talus piles or scree slopes.

Because their mass is greater, larger rocks will have momentum due to gravity and fall down towards the bottom of the slope, while smaller fragments may stop and rest at higher areas on a slope.

Rocks sitting on a slope, large or small, may become unstable and fall to the bottom because of increased lubrication (water falling down the hill during rain), increased weathering and erosion forcing more rocks to fall and collide with the ones in place, or frost melting forcing a water flow down the slope.

2.2.5 - The Lithosphere (KQ2): Earthquake and Volcano Analysis Methods

We've talked a little about the methods used to analyze, and thus prepare and respond to earthquakes, volcanoes, and other hazards, but they are so important to the management of these natural events and the protection of those that are in danger, that we must look at them as a whole.  Pay close attention to the methods...they are vital to your understanding of natural disaster management.  Of course, MEDCs will have more advanced techniques than LEDCs, but both should make use of the best techniques available in order to ensure maximum survival and least destruction.

In the parentheses, "e" will stand for earthquake, and "v" will stand for volcano analysis methods.

Historic Records (e,v)

This one is kind of obvious...but it is important.  Record-keeping is vital to determining where strong earthquake and volcanic activity has happened...because those places are at the most risk.  As you saw in the plate boundary activity, the historical locations of earthquakes and volcanoes have also led us to determine different plate boundaries, and thus determine where the highest level of activity occurs.  Historical records are more accurate in MEDCs, so they have a better chance of aiding in prediction.

Frequency (e,v)

For earthquakes (from USGS website):   "Scientists study the past frequency of large earthquakes in order to determine the future likelihood of similar large shocks. For example, if a region has experienced four magnitude 7 or larger earthquakes during 200 years of recorded history, and if these shocks occurred randomly in time, then scientists would assign a 50 percent probability (that is, just as likely to happen as not to happen) to the occurrence of another magnitude 7 or larger quake in the region during the next 50 years."

This may not be the case, however, as after a slippage, another earthquake may be more likely to occur sooner in the prediction model.

For volcanoes, pretty much the same is true as for earthquakes.  If an area has experience frequent volcanic eruptions, it is assumed that it has a higher probability of eruption than a place that does not.  Once again, however, this is not a very reliable prediction method, especially when it comes to explosive eruptions that have built up over time.  There is always a first eruption, and it may be the worst!

Seismic Evidence (e,v)

Once an earthquake happens, the seismic evidence can let us know where aid is needed by looking at the difference between times of the s and p-waves.  Refer back to the earthquake virtual lab to learn more about how exactly this occurs.  You should be an expert by now!  Of course, knowing where the most damage may be, and also where tsunamis may go, can be a great help in providing aid and relief.

For volcanoes, this is reliable information found on Wikipedia...yes, sometimes it is useful!  " Seismic activity (earthquakes and tremors) always occurs as volcanoes awaken and prepare to erupt and are a very important link to eruptions. Some volcanoes normally have continuing low-level seismic activity, but an increase may signal a greater likelihood of an eruption. The types of earthquakes that occur and where they start and end are also key signs. "  You can read more about using seismic activity as a predictor for volcanoes in Seismic Waves part on the on the volcano prediction Wikipedia site here.  Basically, tremors near a volcano can be a great predictor of eruptions.

Tilt Metres (v)

Read the Wikipedia article on tiltmeters here...best thing we have to predict volcanoes.

Chemical Analysis (v)

Increasing amount of sulfur dioxide in the air can predict that a volcano will erupt, as it is a main component of the effusive gas in an eruption.  The stronger the concentration gets, the more likely it is to explode soon.

Building Design (e)

As we saw in class in the TED Talk on the Haiti earthquake, sound building design is imperative to protecting a population from earthquake disaster.  Properly built structures, with tied rebar and symmetric design are much more likely to hold up than those "built on the cheap."  Investment at the beginning can lead to much less of a human disaster from building collapse.  You can view the TED Talk again here.

Rescue and Aid (e,v)

There are many different organizations that assist in the rescue and aid of volcano and earthquake victims.  As we have seen, however, MEDCs tend to get quicker response because it usually is an established group/government from within the country providing aid, while LEDCs rely on the organizations or governments in the MEDCs for aid.  This provides for not only slower response, but also limited supllies in LEDCs.  The combination of the slow/limited aid, worse prediction technology, and poor building structure puts the LEDCs at a much higher risk of devastation from earthquakes and volcanoes than MEDCs.

2.2.4 The Lithosphere (KQ2): Other Natural Hazards

The "Big 2," of natural disasters may be earthquakes and volcanoes, but other natural hazards (sometimes caused by earthquakes or volcanoes) occur and can be just as devastating.  Here we will discuss those pertinent to your knowledge in this course.

TSUNAMIS

• About
• Series of fast-moving waves that send surges of water on to land.
• Caused mostly by underwater earthquakes, but also by underwater volcanoes and landslides.  The ground moves up and down quickly and energy is transferred to the water, much like if you push a beach ball up and down in the water creating waves (just a heck of a lot bigger).
• About 80% happen in the Pacific Ocean's "Ring of Fire"...a very tectonically active area where volcanoes and earthquakes are common.  You can watch a video about the Ring of Fire here.
• They can move at 800+ km/hr (500 mi/hr)...but may not be felt by boats on the deep water since they do not build tangible height until they near the coast.
• Water will recede from the shore as it approaches the coast, build a giant wall of water, where the top moves faster than the bottom.  Seeing this can warn inhabitants of impending danger, as it usually occurs 5 minutes before the tsunami hits.
• Some tsunamis do not appear as walls, but rather surges of water inland.
• Usually occurs in series...so threat may not be over after initial surge.
• Devastation occurs however far the tsunami reaches inland, as the water cannot be stopped and is very heavy.  It can take down whole building, bridges, and cause massive loss of life.
• Management
• Like all natural disasters, we cannot stop tsunamis from happening.  They are actually a part of Earth's ntural recycling effort...but that does not mean we cannot protect ourselves from potential human catastrophe.  The best thing we can do is prepare residents and buildings of areas that are in the most danger of being affected.  How we do this now is to:
• Have buildings in those areas built to a code that should withstand the force of a tsunami.
• Use sensors attached to the seafloor to detect ocean wave speed and warn those that may be in its path (below is a graphic of these...signal sent to sattelite, then to cities in danger)
• 
• Educate residents of danger areas to evacuate when advised or to flee if they see a water in a coastal area receding quickly and/or abnormally.
• World rescue organizations are able to provide relief...however, education and warning are the biggest help in reducing the negative impact of tsunamis.

LANDSLIDES

Watch the following video to learn about landslides:

Key points to remember:

• Uncontrollable flow of rock, earth, debris, or all 3 caused by earthquakes, excessive rain, erosion, etc.
• Speed determined by material and slope...loose rocks flow fastest (up to 200 mph)
• Slow moving earth, known as soil creep, can be caused by frost, rain loosening up soil, or animals
• It is so slow, that humans have to look for cracks in pavement, leaning power lines, or other destruction to see if it is happening
• Landslides that dump into water can cause tsunamis (has happened in areas behind dams)
• Landslides involving rocks happen in a chain reaction fashion...one or a few rocks falling loosen others, which may be bigger and more destructive
• Slumps - earth moves due to excess groundwater, causing the earth to sink in and move down a slope
• Debris slides - as material falls down  a slope it takes other material with it causing huge losses

Management

Landslide management takes place by knowing which areas are most susceptible and what causes them.  The basic things that can be done are:

• Drainage correction (decrease water buildup)
• Proper land use measures
• Reforestation for the areas occupied by degraded vegetation (decrease erosion)
• Creation of awareness among local population (let people know the signs)

GROUND DEFORMATION

Happens at sites of volcanoes and can let us know what is happening at that site...possibly warning of eruptions or other activities.  See the techniques used to determine the severity here (make sure to click the different techniques on the left).

VOLCANIC ASH

Go to the USGS website here.  Please click the links on the top to learn more specifics on volcanic ash, they give great information you may need on what volcanic ash is.  Also, the many links on the right can let you know what it's like when it falls, and what we can do before, during, and after a volcanic ash event.  There are also many case studies that you will want to peruse to use on your AICE exam.

LAVA

Please read the LAVA section on the following website to get a general idea on how to manage lava.  It usually moves so slow that people can get out of the way, but because it is so hot and heavy, it can destroy buildings and anything else in its path.

LAVA link.

HOT ASH CLOUDS (NUEE ARDENTES)

Pyroclastic flows can cause major damage...there is no way to outrun them.  The best management is to not be in an area of an active volcano.  This site gives a good description of pyroclastic flows (hot ash clouds) and how to best manage in the events.

2.2.3 The Lithosphere (KQ2): Types of Volcanoes

First, watch the following video introducing you to volcanoes, how they form and terms associated with them.  You know some from earlier (and maybe even more), but there is some new important information given.  You may want to watch it more than once and take notes!

Now, read the following from the USGS on types of volcanoes.  Take notes on the types of volcanoes and any key terms you find. We will be using them and the site in class tomorrow.

USGS - Types of Volcanoes

Also, Read about types of eruptions here.  Take notes on the different types of eruptions and any key terms you find:

SDSU - Expolsivity

Click on the links on the left hand side of the SDSU main site to learn other features that may be useful, including lava flow types, pyroclastic flows, gases, and eruption types.

2.2.2 The Lithosphere (KQ2): Earthquakes - Differences in effects in LEDCs and MEDCs

LEDC vs MEDC Earthquake Differences

Why bring a discussion of economic diversity into the study of earthquakes as they relate to the environment?  The different impacts between the two clearly show us that we need to bring LEDCs to MEDC level in order to minimize the impact that they have on the human population.  Do not forget...the main point of environmental science is to sustain life on earth, and there are things we can do to protect ourselves from earthquakes to make our lives more sustainable.

Read the linked case studies that shows the impact of two very similar earthquakes in two very different locations.  Take notes on it...we will analyze it in class tomorrow and watch a video of another case study.

Christchurch (MEDC)          Haiti (LEDC)

2.2.1 The Lithosphere (KQ2): Earthquakes - Causes, Processes, Effects, and Measurement

Earthquakes!

Through television, the internet, and how connected the world is, we've all been witnesses in some way to some of the devastating impacts earthquakes can have.  We will be looking at earthquakes in 2 different sections:  first (this section) we'll take a look at what causes earthquakes, their processes (how they travel, terminology, etc.), general effects of earthquakes, where they happen most often, and how they are measured.  The second section will focus on the earthquakes different effects have in MEDCs and LEDCs and why they are different, though the examination of a few case studies.

What Causes Earthquakes?

The simple answer???  PLATE TECTONICS!  There are some anthropogenic (man-caused) activities, like drilling and fracking for natural gas, that can cause minor earthquakes, but the vast majority are the result of plate movement.  It's quite simple if you think about it...if the plates move vertically or horizontally against each other, any slip will cause movement through waves.  When the waves reach the surface, the energy leaves by massive amounts of shaking that causes destruction.  The place you are most familiar with is probably the San Andreas Fault in California...which are two plates sliding past each other.  The other types of plate movement, divergence and subduction, cause earthquakes as well.


Do a little demo at home


Get an old pencil and bend it.  Put pressure on it by trying to bend it...and more...and more...until SNAP!!!  Did you feel a kind of shock or vibration when it snapped?  That's what happens with earthquakes...the plates try to move, just like the pencil, and finally, when the pressure is enough, vibrational waves travel to the surface, just like the vibrations that reach your fingers.


Processes of Earthquakes

We will look at the processes by examining two diagrams...take a look at the first:

A perfect time to learn the vital terms within it:

• Focus:  The point of slippage in the crust.  Where the waves start.
• Epicenter:  The point directly above the focus on the surface of the earth.  In most cases, it is the location of the most damage.
• Fault:  A fracture in the crust that has been caused by plate movement.  The plate movement then will cause slipping along the fault.

And the second, describing how earthquakes move:

• P-waves:  Compression waves...the first to move.  Travel very fast and not much damage.  Can travel through any earth material.  Go out from focus.
• S-waves:  The second waves to move in...move up and down slowly and cause major damage.  Cannot move through core.   Go out from focus.
• Surface Waves:  rolling waves that stay near the surface.  Can also cause major damage.   Go out from epicenter.

We'll be using these terms/processes in a virtual lab...so learn them!

Stop Here for Day 1

General Effects of Earthquakes

You can hypothesize some of the effects that earthquakes can have...basically this first thing that comes to your mind is damage from shaking.  That type of damage/effect is known as a primary effect of an earthquake...that is, it is a direct result of the earthquake.  Examples of primary effects are building damage, broken bridges, falling debris (could damage humans, animals, or property), landslides, floods (from collapsed dams or river banks), release of hazardous materials, and as we have seen more often lately, tsunamis.  All of these can cause major or minor damage, depending on the severity of the earthquake.

As if that isn't bad enough, there are various secondary effects of earthquakes...effects that happen minutes, hours, or days after an earthquake as the result of a primary effect.  For example, one of the major types of secondary effect is a fire. An earthquake can lead to a busted natural gas pipe or gas tank at a gas station and explosions from broken electrical cables...not that good of a mixture.  This can cause massive fires and damages.  To make maters even worse, water pipes underneath the ground can be broken, so these fires cannot be put out.  Not having available clean water can also lead to an increase in disease spread.

One of the major damage earthquake events in the US happened in San Francisco in 1906.  You may have learned about this in history class...the most damage in San Francisco happened as a secondary effect result of fires.  It also taught us a lot about the effects of earthquakes.  Read more about it at the links below.

History Channel
USGS

Foreshocks are smaller tremors that happen prior to an earthquake and aftershocks are smaller tramors following earthquakes.  Both can cause damage...and surprise people.  Sometimes people think a foreshock is the main earthquake and a larger one comes after and following an earthquake, it is not always time to relax as an aftershock may follow.  Also, don't forget that the worst damage comes at the epicenter of an earthquake...but that does not mean it is limited to that area!

Where Do Earthquakes Happen?

Most of the "big" earthquakes (9/10) happen along destructive (convergent) plate boundaries, although we do know that there are frequent earthquakes at other places like the San Andreas Fault.  This is clearly shown by looking at the two figure below, the first shows the direction of plate movement, and the second shows where earthquakes happen.

How Do We Measure Earthquakes?

As you will see in the virtual lab, we measure earthquake intensity using a seismograph.  The seismograph measures seismic (shaking) activity of the earth.  It is a fairly simple machine, consisting of a roll of paper that is fed continuously under a pencil or pen.  When the ground shakes, the pencil moves back and forth and shows how "intense" the earthquake is.  You can see one below.

A very cool thing about seismographs is that they are set up all over the world, and using data from just 3 of them can let scientists know where the epicenter of an earthquake is (you will see how in the virtual lab). Why is that important???  Well, if we can determine how strong an earthquake and where it started, we may be able to warn people before tsunamis happen.  As technology gets better, we can get information to people better and have the potential to save lives.  There is no current way to predict earthquakes, so this technology is the best way to save people from earthquake damage that we have.

Earthquakes are given an intensity measurement on something called the Richter Scale.  The Richter Scale goes from 0-10+, and each integer (1,2,etc.) is 10x as strong as the previous.  Therefore a 5 is 100x as strong as a 3.  The following table shows you how strong the different numbers on the scale are and how often they occur.

Just a FYI...the 2004 Indian Ocean Earthquake that caused the major Tsunami was a 9.1-9.3 on the scale, the third largest ever recorded (Largest was a 9.5 in Chile in 1960).

Earthquakes are devistating...but they do have different effects in different parts of the world.  You will learn about this in the next section.

2.1.6 The Lithosphere (KQ1): The Rock Cycle

The Lithosphere, essentially the Earth's crust, is constantly, slowly being formed and recycled from the molten rock in the mantle.  One way you have learned about this is through the divergent plate boundaries that bring the mantle to the surface and the convergent boundaries that slide it back down.  These processes are part of the rock cycle, the way that rocks change and are recycled within and on the Earth.

There are three basic types of rock: 

Sedimentary

• Formed from sediments (definition 2), may be eroded fragments of other types of rocks, from dead remains of animals, or from solutions on earth that form solids via chemical reaction (these are called precipitates).
• They can be deposited (through a process called deposition...see below) on both land and in aquatic environments.
• Most common is limestone (Calcium Carbonate - CaCO3), formed in marine environments and is a source of many fossils.
• Sediment accumulates of thousands of years...and can be hundreds of meters thick.
• The pressure of this rock on top of rock is so immense that the sediments fuse together, in a process called cementation.
• Cementation can result in sedimentary rocks such as sandstone and limestone.
• Examples of sedimentary rocks include: conglomerate, breccia, shale, halite, gypsum, coal, and more.  Find out what these look like and more information on each by looking here.

Limestone

Igneous

• Formed when magma (molten rock) cools and solidifies.
• Quick side note...magma is within a volcano or in the mantle, lava is when that molten rock comes out of the volcano...same stuff, different location
• Usually forms beneath the land's surface, called intrusive igneous rock
• intrusive igneous rock cools slowly, since it is below the surface, and forms large crystals
• examples include:  diorite, gabbro, granite and pegmatite
• Some molten rock makes it to the surface and cools rapidly, called extrusive igneous rock
• extrusive igneous rock will have smaller crystals due to the rapid cooling
• examples include: andesite, basalt, obsidian, pumice, rhyolite and scoria
• Pictures and information from both types of igneous rock can be found here.

Granite

Metamorphic

• Formed when igneous or sedimentary rock is under extreme heat and pressure
• Can happen at plate boundaries (pressure) or when in contact with magma (heat)
• Some metamorphic rock forms in layers...this is known as foliated metamorphic rock.
• An example is gneiss...which is formed from igneous granite.  It sure is gneiss!
• Other metamorphic rock has no apparent ordered structure...this is known an non-foliated metamorphic rock
• An example is marble...which is formed from sedimentary limestone.  Wow, this stuff rocks!
• See examples of metamorphic rocks here.

Gneiss

Now that you know the different types of rock, you may be able to put together this whole concept of a "rock cycle."  Before we look at the "big picture," there are three primary processes that happen within it need to be familiar with:

• Denudation - This is the process by which rocks are weathered and eroded.
• Weathering - the breakdown of rocks in situ (they stay in place during the breakdown)
• Chemical Weathering - chemical change of rocks reacting with air or water
• Mechanical Weathering - breaking up of rocks...not altering chemistry
• Biological Weathering - result of plant or animal activity (ex. roots shattering rock)
• Erosion - the breakdown of rocks involving movement of the pieces following
• Movement due to wind, waves, streams, rivers, or glaciers.
• Transportation -  The processes that carry sediment or other materials away from their point of origin. Transporting media include wind, water and mantle convection currents.  Does not break down the rock itself (erosion)
• Deposition - When materials/rocks settle out from whatever is transporting them

FINALLY...let's take a look at the rock cycle...to do this you are going to click the link below to go to a Prezi presentation.  Prezis are really cool...all you have to do is click the arrows and follow along...it will guide you through the cycle!

Rock Cycle Prezi

That was a pretty good, basic understanding of how it works...but it's not limited to just those directions alone...almost all of it can change to the other forms directly as shown by this graphic.

2.1.5 The Lithosphere (KQ1): Evidence of Plate Tectonics

How do we know that the plates have moved...where's the evidence?  We know that earthquakes and volcanoes happen, we know that there are mountain ranges and deep and shallow parts of the ocean...but how do we know it's caused by plate tectonic movement?

This teacher does a really great job of explaining it in terms of paelo-magnetism (see below)...so instead of reinventing the wheel, let's watch him and learn.

KEY POINTS TO TAKE HOME: 

• The continents seem to "fit" together...this is known as geologic fit
• We know from looking at layers of rock that the magnetic poles on Earth switch every so often (by every so often, I mean hundreds of millions of years)
• The magnetic rocks on the crust change poles as you move away from known ridges
• On both sides of the ridge, the distance is the same to change the pole, showing that the rock equidistant from the ridge on both sides was formed at the same time
• The is evidence that the plates are moving away from each other
• This theory and the evidence is known as paleo-magnetism

One more piece of evidence (my favorite) is from what a lot of kids want to be when they grow up when they're in elementary school...dinosaur bone diggers (paleontologists)!  There have been bones of pre-historic creatures (namely the mesosaurus) and plants found on and near South America and South Africa, suggesting strongly that at one point they were connected...there is no other reasonable explanation for finding two of the exact same species that far apart.  This evidence is basically known as paleontology...or fossil evidence.

2.1.4 The Lithosphere (KQ1): Types of Plate Boundaries

When the tectonic plates move, they generally move one of three ways: 

• Away from each other (divergent/constructive)
• Towards each other, with one going under the other (convergent/destructive)
• Sliding alongside each other (conservative/transform)

These three actions have different results on Earth and have shaped what Earth has become today.  BTW...you will see some rock terms, which you can click on to find a definition; however, we will study these more in detail soon when we discuss the rock cycle.

Divergent/Constructive Boundaries

• What happens at these boundaries:
• To "diverge" literally means to go away from one another, so "divergent" plates do exactly that
• They are also considered constructive, because this type of boundary brings mantle to the surface, "constructing" more crust...when in the ocean, this is known as seafloor spreading
• New magma from the mantle rises to the surface to fill the gap between the moving plates
• It is runny lava, which pours out almost continuously in a non-violent way, and cools to form basalt
• This lava forms volcanoes with wide bases and gentle sides

• What happens as a result of this action:
• Rift valleys are formed along faults caused by the crust splitting as the two plates move apart.  (Ex. East African Rift)
• In the ocean, rift valleys result in oceanic ridges. (Ex. Mid-Atlantic Ridge)...really cool...underwater mountains!!!
• Volcanoes and earthquakes can result from divergent plate boundaries

• The following graphic shows the formation of a continental rift valley, a continental rift valley turning into a new body of water, and an oceanic rift valley (ridge)

Click here for an animation of a divergent plate boundary

Convergent/Destructive Boundaries

• What happens at these boundaries:
• To "converge" literally means to go come together, so "convergent" plates do exactly that
• They are also considered destructive, because this type of boundary brings crust back to the mantle, thus "destructing" it
• Usually occurs at oceanic/continental plate boundaries
• One plate, usually the oceanic plate (because it is more dense), sinks below the other
• It is destroyed in the subduction zone
• The subduction zone is the area where the oceanic plate slips under the continental plate
• Sediments on the sea bed between the two plates are compressed and folded up to form the world's high mountain ranges (ex. Himalayas, Rockies)
• The friction from plate movement in the subduction zone makes the rocks melt
• This produces magma from which volcanoes are formed

• What happens as a result of this action:

• These volcanic eruptions can be violent as the lava is shattered into many pieces by explosions, and thrown out as rocks, ash, and other debris
• Tall, steep-sided cones are built up (see picture of Osorno Volcano in Chile to the right)
• Earthquakes are frequent; the ground shakes from the forced movement of rock against rock

• The following graphic shows a typical convergent boundary forming volcanoes on the continent

Click here for an animation of a convergent plate boundary

• A rather unique occurrence of a convergent boundary forms the Rocky Mountains, including the Grand Teton range and unique geothermal features at Yellowstone.  These features are very far inland...not what you'd expect.  The reason being that the subducting lithosphere plate ends up going more horizontal, creating heat changes, and thus mountains and volcanic activity well inland.  A fault (crack in the Earth) combine with this movement gives rise to the majestic Grand Teton mountains.  The following video animation shows this process.  Yellowstone also is over a 'Hot Spot,' which you can see more about in that section below.

Conservative/Transform Boundaries

• What happens at these boundaries:
• The plates slide against each other, neither creating new crust nor destroying it....movement that "conserves" the crust that is in place
• They may be moving in the same direction, at different speeds, or in opposite directions
• Stresses build up, which are then released by occasional, sudden plate movements 
• Friction caused by rock rubbing against rock forms earthquakes

• What happens as a result of this action:
• Earthquakes...fault likes (Ex. San Andreas Fault)
• Landslides, fires, and other destructive forces can be the result of earthquakes caused by conservative boundary shift

• The following graphic shows an example of a conservative boundary

Hot Spots

The last phenomena you need to know about in this part are called hot spots.  Hot spots aren't really the result of plate movement...they can be at a plate boundary, near one, or far from one.  They are theorized to be the result of extra-hot mantle pockets that push their way to the surface.  They can result in things such as volcanic islands and geysers.  Two great examples of these are the Hawaiian Islands and the Yellowstone Caldera and resulting Geysers, both in the middle of plates.  The spread of the land masses will happen as the plate the hot spot is under moves, but the hot spot remains stationary, like in the Hawaiian example shown here: