WELCOME TO CLASS, EVERYONE!!
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•
This session will be recorded for educational purposes.
ANNOUNCEMENTS
• Start recording, Mrs. Owens!
• End of quarter is: NOVEMBER 6th!!
• Please check your grade – if you are behind REACH OUT TO
ME! I can help you get caught back up.
• We have begin entering grades for attendance – make sure
you fill out your form!
•
How it will work…
• Submit your jokes!
ITEMS DUE THROUGH TODAY:
• Benchmark
• Quiz 1.05
• 1.11 Unit Test
• Quiz 2.03
• Pangea Gizmo
• 2.12 Mid-Unit Test
• USA TestPrep Earthquakes Quiz
• Quiz 2.18
ITEMS DUE THIS WEEK
• 2.20 Unit Test
• Study guide up tomorrow – review available during office
hours!
VOLCANOES
THEY’RE SO LAVABLE!
VOLCANIC ZONES WHERE DO VOLCANOES
HAPPEN?
• Divergent boundaries – plates moving apart
• Convergent boundaries – subduction zones
• Hot spots – caused by plates moving over
mantle plumes
• The type of boundary and where it occurs
will determine the type of volcano!!
HOW DO VOLCANOES
FORM?
• Increased heat, decreased pressure, and
water interact to melt some mantle rock.
• These rise and pool just beneath the crust in
magma chambers.
• The magma melts rock in the crust above
the chambers and erupts to the surface
through a vent.
MAGMA TYPE DETERMINES THE
TYPE OF VOLCANO
• When magma pools below the crust, it partially melts
and mixes with the rock in the crust. This changes its
makeup!
• Three things affect what kind of magma will erupt:
• Silica content –
• High silica, more explosive
• Low silica – less explosive
• Viscosity – resistance to flow
• how thick the magma is and how it flows
• high viscosity resists flow (honey), low
viscosity does not resist flow (water)
• Gas content
MAGMA TYPES
• BASALTIC - RUNNY (LOW VISCOSITY), LOW SILICA CONTENT, LOW
GAS CONTENT
• FORMS SHIELD VOLCANOES OR FISSURE ERUPTIONS
• BASALTIC - LOW SILICA WITH HIGH GAS CONTENT
• FORMS CINDER CONE VOLCANOES
• ANDESITIC/RHYOLITIC – THICK (HIGH VISCOSITY), HIGH SILICA AND
GAS CONTENT
• FORMS COMPOSITE VOLCANOES (STRATOVOLCANOES)
• VISCOSITY VIDEO!
VOLCANOES THROW OUT
LOTS OF THINGS!
• Gas – water vapor, carbon dioxide, sulfur dioxide
(causes acid rain), and hydrogen sulfide
• Lava
• Pyroclastic materials – fragments of rock, volcanic
glass, and lava!
• Tephra – the name for pyroclastic debris
• Ash – fine particles of rock
• Dust- even finer particles than ash
• Can cause lahars – landslides and mudflows, volcanic
debris, and water can cause a great deal of damage
SHIELD VOLCANOES!
• Basaltic magma with LOW VISCOSITY and LOW GAS
CONTENT form shield volcanoes!
• Non-explosive eruptions
• Runny lava seeps out of fissures and cools – forms
layers
• Eruptions continue over long periods
• Forms a broad-based, gently sloping volcano
• Shallow magma chambers and broad, collapsed opening at
the top called a CALDERA.
• Magma can seep out of cracks and fissures along the sides
of the volcano.
• Shield volcanoes erupt continuously
• Eruptions can last a hundred years or more!
FISSURE ERUPTIONS
•
Fissure eruption - low-viscosity magma can
seep through a fissure in the crust and flow
out onto the surrounding land. Because the
lava is runny and has little or no gas, the lava
runs a long distance before cooling and there
is no explosive eruption.
•
Instead of forming a volcano, this type of
eruption forms horizontally layered plains of
basalt called flood basalts or plateau basalts.
CINDER-CONE VOLCANOES
• Cinder-cone volcanoes are formed when basaltic lava
(low silica magma) with a HIGH GAS CONTENT erupts.
• The explosive eruption expels gas, ash, dust, and
pyroclastic material. The pyroclastic material goes high
into the atmosphere and falls down around the vent
where it builds up, loosely packed, to form a steep
cone.
• The top of the cone has a steep crater that leads into
the central vent, which is filled with rock fragments.
• Some cinder cones also have lava flows from their
base.
• Cinder cones generally erupt only once and for a short
time—a few weeks to a few years.
COMPOSITE-CONE VOLCANOES
• Andesitic and/or rhyolitic magma with high-viscosity and high-gas content
forms composite-cone volcanoes.
• The eruptions are explosive and the thick lava pours out only a short
distance, where it cools.
• Multiple eruptions provide layer upon layer of lava to form a steeply
sloped cone called a composite-cone volcano. Material that falls back to
earth around the volcano adds a broad, gently sloping base to the
volcano.
• Composite-cone volcanoes are long lived. They typically have long periods
of dormancy interrupted by shorter periods of explosive eruptions.
• The volcanic mountain is composed of numerous layers of cooled lava
and the base of accumulated pyroclastic material. There may be
secondary vents and fissures on the sides called fumaroles that extrude
lava and gas from the main conduit.
TO DO FOR THIS WEEK:
• Prepare for Unit Test
• Continue work in OMHS
• Make sure you are up to date with your assignments
• Fill out attendance form:
•
https://docs.google.com/forms/d/1Z1WbS0EJaJO3oFP78zOQG0
5wn_M3roHSH-sVpnmmyQM/edit
VOLCANOES AT DIVERGENT
BOUNDARIES
• Molten rocks from the mantle rise, break through the crust, and
push plates apart at divergent boundaries.
• Undersea—Molten rock passes through the mantle and oceanic
crust and erupts through a fissure in a quiet, nonexplosive
manner.
• The rising mantle rocks and the oceanic crust are basalt, so
the lava is basaltic. It comes out as pillow lava (much like
toothpaste from a tube) and flood basalt.
• Continent—Magma comes from partially melted mantle (basalt)
and continental crust (granites) and erupts non-explosively
through a rift. The lava consists of basalt and rhyolite.
VOLCANOES AT CONVERGENT
BOUNDARIES
• At convergent boundaries, one plate sinks under another, the sinking plate
partially melts, and the molten rocks rise through the overlying plate.
• Oceanic-oceanic convergence
• Magmas consist of mantle and the ocean plates themselves
• Erupt explosively (trapped steam – high gas content)
• Form volcanic island arcs
• The lava tends to be mostly basalt and some andesite
• Oceanic-continental convergence
• Magmas consist of mantle, oceanic crust, and continental crust
• Erupt explosively
• Form composite and cinder cones along the continental margins.
• The lava tends to be andesite, and rhyolite.
VOLCANOES AT HOT SPOTS
• Where a plate moves across a rising mantle plume, you have
a hot spots. Hot spots can occur on land or in the sea.
• In the ocean, rising molten rocks from the deep mantle melt
through the ocean crust (basalt)
• Erupt non-explosively on the ocean floor, and
• Build up shield volcanoes, which become chains of volcanic
islands.
• The lava consists of basalt.
• The Hawaiian Islands are an example of this type of hotspot volcano.
• On the continent, the rising molten mantle rocks must pass
through continental crust (granite)
• Erupt non-explosively through fissures.
• The lava tends to be flood basalt and rhyolite.
BRAIN BREAK!!
• Samantha’s sweet hamster, Cookie, will make us all feel happier!
I just lava her!
• Take a moment to enjoy her TINY HANDS and stretch/dance/relax
for a bit!
MOUNTAINS AND FAULTS!
FAULTS
• A fault is a fracture or zone of fractures between two blocks of rock.
This fracture or break can be caused by tectonic movement.
• Pressure and movement between two rocks can cause displacement
at the fault line.
• There are several different kinds of faults.
•
Reverse faults
•
Normal fault
•
Strike-slip fault
FOLD MOUNTAINS AND EROSION
• Fold mountains occur when tectonic forces cause rocks in the crust
to fold.
• When two continental crust collide, or converge, they fold upward
or uplift to form mountains.
• Rocks fold during mountain building, but the ridges and valleys we
recognize as mountains are not necessarily the high and low parts of
the fold.
• Different rates of erosion create ridges and valleys.
• Weathering erodes the rock, but because different layers have
different resistances, the rocks erode at different rates.
• Weak rocks erode rapidly to become valleys, while more-resistant
rocks erode slowly and become ridges.
OCEANIC/CONTINENTAL VOLCANIC
MOUNTAINS
• When plates collide, some type of mountain is formed. The mountain
type depends on the type of plate boundary.
• When two oceanic crusts collide, one usually sinks beneath the
other. The subducted plate takes seawater with it and partially melts
So, oceanic-oceanic convergence gives rise to volcanic mountains that
rise above the sea as volcanic island arcs.
• Oceanic-continental convergence gives rise to continental volcanic
mountains. When dense oceanic crust converges with continental crust,
it sinks beneath the continental crust at deep ocean trenches.
Volcanoes break through the crust, forming a range of coastal
volcanoes.