Reading #1
Katie Brandeberry
What we mean by plate tectonics
Think of earth as an egg. A cracked egg which has been hard boiled and the shell moves over the eggs
surface. Visualize the pieces of the shell as the earth’s plates.
Each actual plate is approximately 100km thick and the surface area is thousands of kilometers.
Development of a unifying theory
Francis Bacon and Antonio Snyder had noted similarities on fossils around areas of the world which were
widely apart.
Later Seuss suggests that the continents were once one large land mass. Based off these findings in the
early 1900s Alfred Wagener and F.B. Taylor proposed the continental drift theory.
Fossil Record
Due to size in seed and fossil distribution in different continents, biologist, believe that there was once
only one large continent.
Distribution of organisms around the continents could be explained by this theory of Pangaea. Ages of
rocks on the continents and geologic structures like mountain ranges, and distribution of glacial deposits
would match up if the continents were joined together.
Paleomagnetism
Some rocks are weakly magnetized. There are a few different continents which each point to a different
magnetic north suggesting two things. Either that there were at some point three different locations of
the magnetic north at the same time; or, that there were three completely different locations of the
magnetic north.
Those two situations are impossible. After research, geologist, have decided that the continents have
moved over time. And through research and GPS data they know that they are continuing to move.
Ages of Seafloor Rocks
Through exploration geologist have found that on the sea floor there are ridges, mountains and rift
valleys. The Sea Mountains are formed out of igneous rock and basalt; while, the rift valleys are found at
the crests of these undersea mountains.
Rift valleys are a series of cracks which are located in the earth’s crust and where the plates are being
pulled away from each other. Lots of these valleys are called mid ocean ridges. The mid Atlantic ridge is
Seafloor Spreading
Where there are weaknesses in the earth’s plates magma can rise. This occurs at rift valleys.
There is a phenomenon called sea floor spreading; this occurs when igneous rock is formed and is
pushed away from the crest. When this occurs new crust is formed.
Convection cells- Cause of Plate Motion?
Some investigators believe there are two layers of convections sells which can be found inside of the
mantel. There is an idea which suggests plate motion brings hot rock to the centers of convection cells
where it then becomes magma. After this it turns solid. The plates are then carried horizontally and heat
loss occurs as it shifts downward; then it occurs again in a cycle.
In the past few years there has been uncertainty that convection cells could result in observed
distribution and movement of plates in the lithosphere. Due to this, scientist, have proposed other
mechanisms to explain the plate movement.
Ridge Push and Slab Pull
There are two forces which are related to gravitational and thermal effects used to explain plate
movement. These two forces are called ridge push and slab pull.
Ridge push gets its name from its movement. The youngest part of the Lithospheric plate is at the top.
The lithospheric plate is pushed by gravity towards the plastic Asthenopshere where it pushes on the
rest of the plate. The slab pull is considered by most geologist to be the reason for the driving for of
plate tectonics.
Plate Boundary Types
There are three types of plate boundaries found in the Lithosphere. Convergent, Divergent and
Transform plates are the three kinds.
A divergent plate boundary occurs in areas like mid ocean ridges and on continental crust. This is where
two plates move away from each other. The seconds is a Convergent boundary; which is, where plates
move towards each other. This type of boundary occurs at mountain ranges, and earth quakes
commonly occur. The last plate boundary is called the Transform fault boundary. This type of plate
movement occurs where the two plates rub against each other in a lateral movement. These
movements cause major earthquakes.
Conclusion
Lithospheric plate interactions result in mountain ranges, metamorphic rock and volcanic eruptions, etc.
However plate exact movement is still uncertain.
The heat released from the earth’s interior is what makes all plate tectonics possible. The plate tectonics
theory provides an explanation for these geological phenomena. Continuing research will help result in
better understandings of how our earth and these plates change over time.
Reading #2 Volcanoes
Volcanic eruptions and volcanoes
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Most volcanic activity is associated with plate boundaries. Not all is but the most frequent and
sometimes destructive.
Gases: volcanic gases are mostly made of water vapor and carbon dioxide. There are a few others
Liquids: the product which is liquid is lava. Some lavas are fso fluid that they spead out before
solidifying and cover significant areas.
Solids: called pyroclastics which represent solidified fragments of magma.
Volcano features
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Volcanoes are formed when the molten rock comes up through crack and vents in the earth’s
surfaces from the earth’s interior.
When the molten rock emerges it creates a dome shaped structure.
A crater is a steep funnel shaped depression at the top of volcanoes.
Zones of volcanic activity
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There is a volcanic zone called the ring of fire; where the volcanic activity zone is a circular shape.
The third main zone is in Iceland through the middle of the Atlantic Ocean.
Hot spots and volcano formation
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The Hawaiian islands are still being formed today above a hot spot
Hot spots are essentially stationary and the above plates move.
Active Volcanoes eventually move away from the hot spots.
Impact on humans
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Volcanoes often have a negative impact on humans.
One of the most devastating volcanic eruptions happened in Martinique in 1902.
However, lava flow is slow and to slow to pose a threat. The five most explosive volcanic eruptions
in the past 200 years
Significant eruptions
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7000 large animals and thousands of small animals perished due to Mount St.Helens
Eyjafjallajokull volcano erupted again in 2010, filling areas with lava melting snow and destroying
roads and farms.
Volcanic eruptions a long term perspective
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The volcanic explosivity Index is used to describe size and explosivity of volcanic eruption
Here are the 5 most explosive eruptions from the past 200 years: Tambora, Krakatobe, Novarupta,
Pinatubo and Santa Maria.
Volcanic eruptions a long term perspective
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It’s difficult to determine eruptions when they will occur and how devastating they will be.
Positive contributions of volcanoes: create terrestrial landscapes, volcanic emitions are important
sources for materials such as pumice ammonia and boric acid etc.
Conclusions
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Volcanic activity is very important to building the earth’s crust and lithospheric plates.
Some eruptions do not form volcanoes but spread very far. Some eruptions are explosive and
create volcanoes with steep slopes.
Reading #3 Earthquakes
Katie Brandeberry
Earthquakes: what are they?
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Sudden release of energy which results from the breaking or slipping of deformed rock within the
earth’s crust, causing an earthquake.
Seismic waves are transmitted by earthquakes
Earthquakes how and where they happen
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Most major earthquakes occur at plate boundaries which converge or diverge.
Some of the biggest earthquakes at affect the U.S. occurred in the east.
Earthquakes, rock movement and faults
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Displaced rocks which occur during earthquakes are called faults.
If there is a rock below the fault it is called a footwall block.
Earthquakes focus and epicenter
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The epicenter is generally where most seismic waves will be felt the strongest.
The point on earth’s surface directly above the focus is the epicenter.
Detecting earthquakes
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Around 1 million earthquakes are estimated to take place each year
When an earthquake occurs, because of the suspended weight, it and the pen (seismograph) stay
stationary.
P S and L seismic or Earthquake waves
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P waves are primary which move at 7/8 km per second.
L waves are long was which move the slowest out of all 3 waves.
All 3 are generated simultaneously
Measuring earthquakes
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Until around 1980 they were measured with the Richter Magnitude Scale.
The Mercalli scale recognizes different levels of destruction, ground motion and impact on humans,
which assigns a roman numeral.
Tsunami
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This Japanese word means wave; which are triggered by earthquakes in the seafloor.
Tsunamis are confused often with tidal waves and they travel rapidly across the ocean.
Earthquake damage
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No construction design is absolutely earthquake proof.
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Areas of soft sediments like landfills have a greater damage than buildings in areas with solid rock.
Earthquake predictions
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Successful prediction must give an accurate location, time and magnitude. We cannot do this yet.
The best geologist and seismologist predict this will occur within decades to years.
Conclusion
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Earthquakes occur almost everywhere mostly near plate boundaries.
It is possible thus far to make structures more resistant to damage by earthquakes, but still
impossible to create completely resistant structures.
Reading #4 Rocks and minerals
Plate tectonics
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Earths plate consists of rocks composed of many minerals, plus thin covering of soils
We often think of continental movement, mountains and volcanoes as those aspects of gology
explained through plate tectonics.
Minerals
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A mineral is naturally occurring an inorganic crystalline material with a unique chemical
composition.
Minerals in the earth: Feldspar, Quartz, Mica, clay and calcite. Those are a few common known
minerals.
Rocks
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Normally rocks are mineral aggregates. However some are fossil remnants.
Igneous, sedimentary, metamorphic are just a few types of rocks.
Identity of a rock or mineral provides clues as to the type of environment where it formed.
Conclusion
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Specific rocks and minerals form in response to environmental conditions.
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Locating and identifying these helps to determine past environmental conditions too.