Download Volcano Notes _filled in_

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Updated 3-22-13
This material can be found in the Catastrophic Events book (pages 198-273) and in your
ScienceSaurus (topics 179-197).
Good BrainPOPs to watch on this topic include: Volcanoes, Rock Cycle, Types of Rock,
Weathering, Erosion and Mountains.
There are also some PowerPoint presentations that we have been looking at in class on Mr.
Abe’s website.
Types of Volcanoes (Lesson 20):
Focus Question: What are the 3 main types of volcanoes and what are their properties and
examples?
-Stratovolcanoes are large layered volcanoes with sticky gassy (high viscosity) magma that
results in short explosive eruptions that result in major devastation to the landscape.
Stratovolcanoes are located at subduction zones (convergent plate boundaries) and form
the “Ring of Fire”. Examples include Mt. St. Helens, Mt. Rainier, Mt. Fuji, etc.
-Shield volcanoes are wider than they are tall (flat) volcanoes with very hot runny (low
viscosity) magma that result in slow oozing eruptions that can last a long time. Shield
Volcanoes form at hotspots that can be located at a plate boundary (like Iceland) or way
out in the middle of a plate (like Hawaii).
-Cinder Cone Volcanoes are smaller volcanoes that have hot gassy magma that result in
small explosive eruptions that can last for a fair amount of time. Cinder Cone Volcanoes
can be found near other volcanoes (like Wizard Island, Crater Lake) or in areas where no
volcanic activity had previously occurred (like Paricutin, Mexico).
Magma and Lava Lab (Lesson 19):
Focus Question: How do magma and lava change the surface of the Earth?
-Magma can have different viscosities based on many factors including its temperature.
-The hotter the magma the lower the viscosity. This would be like the runny magma of a
shield volcano.
-The cooler the magma the higher the viscosity. This would be like the more sticky magma
of a stratovolcano.
-Magma with higher viscosity creates earthquakes as it pushes its way up through the
crust. Often times the magma won’t reach the surface and create a lava dome (a bump
with cracks) as a result.
-Hotter magma with lower viscosity burns through the crust and runs on the surface until
it pools and cools or comes in contact with water and cools. This would create the layers
of volcanic rock or pillow lava (like Hawaii).
-Sometimes the magma leaves the magma chamber and the top of the volcano collapses
making a special landform called a caldera (Crater Lake).
-As magma and lava make their way to the surface and cool they form new landforms and
new rock to build up the Earth’s crust.
Lahar Lab:
Focus Question: What story can layers of rocks tell us about the landscape?
-The Principle of Superposition tells us that the older rock layers are on the bottom and
the newer rock layers are on the top. This can help us find the relative ages (newer than,
older than) of the rocks.
-A lahar layer tells us there was a landslide caused by a volcanic eruption, earthquake,
flooding or some other major event.
-A tephra (ash) layer tells us there was a major volcanic eruption and the type of ash can
tell us which volcano it came from.
-The layers of an area can tell us about the geologic history of that region. The rocks tell
us the story of the landscape.
Newest Rock
Oldest Rock
Igneous Rock Lab (Lessons 21 and 22):
Focus Question: What story can individual rocks tell us about the landscape?
-Minerals are the ingredients that make up rocks. We can learn where a rock could
possibly be from based on the types of minerals in the rock.
-A clump of minerals is called a crystal. Sometimes crystals have very specific patterns and
those patterns help us identify the crystals.
-Rocks that cool quickly have small crystals. Rocks that cool slowly have larger crystals.
-If a rock has small crystals we can infer that the rock was probably lava that cooled
quickly on the surface. We call these rocks extrusive rocks (extra=beyond/outside).
-If a rock has large crystals we can infer that the rock was probably magma that cooled
slowly inside the earth. We call these rocks intrusive rocks (in=inside)
Rock Cycle Online Activity:
Focus Question: What are the types and properties of the three main types of rocks and how can
they change from one type to another?
-Sedimentary rocks are rocks that are made from layers of sediment (sand, pebbles, shells,
etc) that build up and then undergo compaction and cementation to form rock with layers.
-Igneous (fire) rock is formed when magma or lava cools to form a rock.
-Metamorphic rock is rock that is formed when igneous or sedimentary rock are
introduced to intense heat or pressure and changed. Metamorphic might have layers and
crystals that are warped.
-Weathering and erosion can break all 3 types of rocks down into sediment.
-Plate tectonics can push all 3 types of rock into the mantle to melt back into magma.
-Take a look at the rock cycle diagram on page 250 in your Cat. Events book or page 180 in
your ScienceSaurus or head back to the interactive activity at
http://www.learner.org/interactives/rockcycle/index.html
The Principle of Super Position and Unconformities:
Focus Question: What things can happen to change the stories of the rocks?
-The Principle of Superposition tells us that the older rock layers are on the bottom and
the newer rock layers are on the top. This can help us find the relative ages (newer than,
older than) of the rocks.
-Unconformities are changes that occur in the rock layers (strata).
-Unconformities can be caused by plate tectonics (earthquakes), volcanic activity (magma
pushing and lava flows), erosion (water and glaciers), lack of deposition (no new sediment is
deposited over a long period), etc.
-Unconformities can add rock layers (add chapters), shift rock layers around (rearrange
chapters), erase or delete rock layers (delete chapters) or maybe there is just a long period
of time where there were no layers deposited (no middle chapters written).
Weathering and Erosion:
Focus Question: What processes break down the earth’s crust?
-Weathering and erosion can be mechanical or chemical.
-Mechanical erosion is when the rock is broken down by water, wind, sand, freezing and
cooling, glaciers, living things like tree roots, etc.
-Chemical erosion occurs when the rocks react with chemicals and are broken down.
Some examples are acid rain and oxidation (like rusting).
-In either case rocks are broken down smaller and smaller until they form sediment and
then can be changed back into sedimentary rock by compaction and cementation.
Hint, Hint, Wink, Wink Question:
Explain the processes that can change the three main types of rock into another type of rock. Be
sure to include the names of the three types of rock.
http://www.learner.org/interactives/rockcycle/index.html
Other Stuff: (Information learned from BrainPOPs and other activities.)
-Living things also play a role in the story of rocks and rock formation.
-Fossils are traces of organisms that are preserved as rocks. They can not only tell us what
living things were living in the area, but also provide us clues about the climate and other
conditions of the past. Fossils can also help us find the age of rock layers if we know the
relative age of when the organisms were on earth we can infer that the rocks are about
the same age.
-Coal is formed from swamp plants that decay into peat. Peat can then be compressed and
turned into rock (coal). A coal deposit in the landscape would suggest that at one point
there was a swamp-like habitat.
-Coral is the “skeleton” that the actually little animal corals build to attach themselves to.
Minerals from the water are used for the coral. Finding coral suggests that there was a
warmer body of salt water at one point. (Usually coral grows in present day tropical
oceans.)
-Limestone is formed by the shells of marine invertebrates piling up layer after layer and
compressing into rock. There is a great deal of Calcium and Carbon that make up the
shells of these marine invertebrates. Limestone deposits suggest that there was a large
body of salt water at one point.
-The K-T Boundary is a rock layer that was deposited about 65 million years ago. There are
higher levels of a radioactive element called iridium in the rock. It is thought that the
rock that makes up the K-T boundary was deposited when a giant asteroid hit the earth
kicking up a dust cloud so big that it settled over the entire Earth. A huge crater that is
also dated to about 65 million years ago was discovered off of the Yucatan Peninsula of
Mexico. It is widely accepted that this asteroid impact is what killed off about 90% of all
species on Earth including dinosaurs. Dinosaur fossils are found below the K-T Boundary
but no dinosaur fossils are found above the K-T Boundary.
-Volcanologists (scientists that study volcanoes) can make short term predictions of
volcanic eruptions by looking at the number of earthquakes near the volcano. As magma
pushes its way up to the surface there is pressure that builds and then eventually the
rocks break. This leads to a much higher frequency of earthquakes under the volcano.
Before the eruption of Mt. St. Helen’s there was also a large bulge (lava dome) that was
growing on the North side of the mountain as the magma rose. This gave anyone that
wanted to time to evacuate to safety and no one was surprised by the eruption.