Transcript Volcanoes, Hotspots, and Earthquakes

Earthquakes, Volcanoes, and
Hotspots oh my
Objective:
Describe how earthquakes waves are
generated and how earthquakes waves
move throughout the earth.
Epicenter & Focus of Earthquakes
Epicenter—Location directly above EQ on Earth’s surface.
•Focus
Focus: or hypocenter; point within Earth where
the EQ occurred.
Body Waves and Surface Waves
Surface waves
travel along
Earth’s surface.
Body waves
(P and S)
travel inside
Earth.
While P- and S- waves radiate outward in all directions, surface waves travel
along the surface of the earth and decrease in amplitude with depth.
Earthquake prediction eludes us.
EQ forecasting
is more realistic
and perhaps
more useful.
(Probability of an
earthquake)
What is the difference?
Possibility of a 6.7 EQ along the San Andreas fault based off
Historical earthquakes in specific locations.
• Tension- force that pulls on the crust
resulting in the center becoming thinner
• Gum being pulled apart
• Compression- force that squeezes a rock until
it folds or breaks
• Trash compactor
• Shearing-force that pushes a mass of rock in
two opposite directions
• Deformation = any change in volume or shape
of Earth’s crust
Sketch TYPES OF STRESS in notes!
TOO Much Stress!!!!
• Fault (Plate Boundaries + many more)
obreak in the crust
oslabs of crust slip past each other
oThink of breaking a candy bar in two… first it
will bend and stretch, but with enough stress
it will snap
Strike-Slip Fault
• Caused by shearing
motion
• Associated with
transform plate
boundary
• Example
oSan Andreas Fault
The average rate of
motion across the San
Andreas Fault Zone
during the past 3 million
years is 56 mm/yr (2
in/yr). This is about the
same rate at which your
fingernails grow.
Assuming this rate
continues, scientists
project that Los Angeles
and San Francisco will be
adjacent to one another
in approximately 15
million years.
Strike-slip
Volcanoes
Volcan Masaya,
Nicaragua
What is a volcano?
vent
cone
conduit
• Volcano is a vent or
'chimney' that
connects molten
rock (magma) from
within the Earth’s
crust to the Earth's
surface.
• Includes the
surrounding cone of
erupted material.
magma
chamber
Volcanoes are formed by:
- Subduction
- Rifting
- Hotspots
How and why do volcanoes erupt?
• Hot, molten rock (magma) has a lower density
than surrounding rock and rises due to
convection. Magma works its way through
cracks in the crust to the surface.
• Large amounts of gas and a high viscosity
(sticky) create explosive eruption!
• Small amounts of gas and (or) low viscosity
(runny) magma will form an effusive eruption
What is Volcanic Activity?
• An opening in Earth’s
crust through which
molten rock, ash &
pumice (pyroclastics)
and gases erupt.
• The landform that
develops around the
opening.
• A way for Earth to
release heat energy
from the interior due
to radioactive decay.
-TWO KINDS
-Explosive:
where
rapidly escaping gas
bubbles (= vesicles) rip
apart
the
magma,
fragmenting it.
-Effusive: where the
D. Peebles
magma
leaks out onto
the surface passively as
lava flows.
Volcanic Hazards
•
•
•
•
•
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Courtesy of www.swisseduc.ch
Pyroclastic flow
Lahars/Mud flows
Pyroclastic fall
Lava flow
Noxious Gas
Earthquakes
What are the Types of Volcanoes?
Composite (Stratovolcano)
Shield
G. Vaughn
USGS
Mt. St. Helens, WA
Mauna Loa, HW
Cinder
A. Heisey
Sunset Crater, AZ
How Do Volcanoes Differ?
• Size
• Shape
• Composition
• Location
Tarbuck & Lutgens
Shield Volcanoes
• Small amt. pyroclastics
(cinders, ash)
• nonexplosive
eruptions
• Hot spots and ridges
(mantle material)
• Structure
• Slope 1-5o
• Most form Islands
• ocean to ocean
convergence.
Tarbuck & Lutgens
Cinder Cones
• Large amt.
pyroclastics
• Structure
• Slope - 30o to 40o
• 100-1000 ft height
• Deep crater
A. Heisey
Tarbuck & Lutgens
Cinder Cones
Pelee’s Cinder Cone, HW
Fire Fountain=Pyroclastics
USGS G. Lewis
USGS G. Lewis
USGS G. Lewis
Parasitic Cone
Composite(Stratovolcano) Volcanoes
• Large amt. pyroclastics
• Viscous lavas
• Explosive / catastrophic
eruptions
• Subduction boundaries
• Structure
• Symmetrical cone
• Steep summit, gentle
flanks, Slope 10-40o+
• Ring of Fire
• Massive earthquakes
M. Giannechini
Pomerape & Parinacota, Chile
Pacific Ring of Fire
Hotspot
volcanoes
Volcano Monitoring
Volcano Observatories
are set up on all active
volcanoes that
threaten the human
population. These are
designed to monitor
and potentially to
predict the eruptive
behaviour of the
volcano in question.
What are Hotspot Volcanoes?
• Hot mantle plumes breaching the surface in the
middle of a tectonic plate
The Hawaiian island chain are examples
of hotspot volcanoes.
Photo: Tom Pfeiffer / www.volcanodiscovery.com
The tectonic plate moves over a fixed
hotspot forming a chain of volcanoes.
The volcanoes get younger from one end to the other.
Yellowstone
National Park
North American
Plate slowly
moving
southwest over
existing
hotspot
Seismic Activity
• Earthquake activity commonly precedes an eruption
• Result of magma pushing up towards the surface
• Increase volume of material in the volcano shatters the
rock
• This causes earthquakes
Quiz
8. ________ is made of the crust and upper mantle.
9. What are the 3 types of plate boundaries?
10. What are the 3 types of faults?
11. What causes a fault?
12.What is the location directly above
an earthquake on Earth’s surface?