Transcript File - Hoblitzell`s Science Spot

The Structure of Earth
1. INNER CORE
•The very center of Earth (like the seed
inside a peach pit)
•SOLID
•composed of Fe and Ni
2. OUTER CORE
•(the pit of the peach that surrounds the seed)
•LIQUID
•composed of Fe and Ni
•Slowly flows at several km/yr
3. MANTLE
THICKEST LAYER (~3000 km)
(the thick juicy part of the peach)
•composed of Si, O, Mg, Fe, and others
LOWER MANTLE – from outer core to
~350 km below surface
MANTLE
UPPER MANTLE - described as plastic-like;
characteristics of a solid but will flow like a liquid
when under pressure like SILLY PUTTY!!
•Extends from bottom of crust to ~350 km deep
•ASTHENOSPHERE – lower part of upper mantle;
flows more easily than rest of mantle
•LITHOSPHERE - ~100 km thick and includes upper
most part of mantle and ENTIRE CRUST
•Rigid, brittle, and doesn’t flow
www.geog.ouc.bc.ca/physgeog/contents/ images/lithosphere.gif
Crust/Mantle Boundary discovered 1909 = MOHO
4. CRUST
Outermost layer (the skin of the peach)
TWO TYPES OF CRUST
A. CONTINENTAL CRUST
similar composition to granite
thick (~20-60 km) and light (density ~2.7)
B. OCEANIC CRUST
similar composition to basalt
thin (~5-10 km) and dense (density ~3.5)
HOW DO WE KNOW??
Seismic (Earthquake) wave data
Rock Core samples - GLOMAR
CHALLENGER
Drilling Vessel
GLOMAR
CHALLENGER, Deep
Sea Drilling Project,
SIO, 1968
DSDP image
www.www.gly.fly.edu
www.gly.fsu.edu/.../ GLY1000/Chapter3/Slide7.jpg
Combines theories of Continental Drift and Seafloor
Spreading
Earth’s crust and upper mantle (lithosphere) are broken into
thin sections called PLATES.
These plates move around on the mantle (asthenosphere)
Plates are made up
of the Lithosphere rigid layer ~100km
thick
ASTHENOSPHERE plastic-like layer below
lithosphere
The lithospheric plates float on the denser asthenosphere
The plates move along plate boundaries in one of three ways:
1. PULL APART
2. COME TOGETHER
3. SLIDE PAST
Mountain building, Earthquakes, and Volcanoes are the result of
plate movement = TECTONIC ACTIVITIES
earthguide.ucsd.edu/.../ tectonicplatessio.gif
WHY DO PLATES MOVE???
• Lithosphere rests upon plastic Asthenosphere
• Flow in astheno due to large slow moving
CONVECTION CURRENTS
•
Hot material expands & rises
•
Cool material contracts & sinks
• New material rising at Earth’s surface & pushes old
material aside DRIVING PLATES APART
• Where cooler material sinking, PLATES PULLED
TOGETHER
www.geog.ouc.bc.ca/.../contents/ images/tectconvection.gif
Spreading center
Ocean
trench
Subduction
Oceanic crust Oceanic crust
zone
Continental
crust
Continental crust
Material cools Cold dense
as it reaches material falls
the outer back through
mantle
mantle
Mantle Hot material
rising
convection
through the
cell
mantle
Two plates move
towards each other.
One is subducted back
into the mantle on a
falling convection
current.
Mantle
Hot outer
core
Inner
core
Fig. 14-3, p. 346
RIFT VALLEY
Plates move away from each other: volcanic activity and
earthquakes
EX: MORs - Mid-Atlantic Ridge - North America & Europe
slowly moving away from each other
EX: On Land - East African Rift Valley - valley formed where
plates are separating
maritime.haifa.ac.il/departm/ lessons/ocean/wwr80.gif
Earth: Animation List
Plates collide with each other & one plate may be destroyed!
Three Types of Convergent Boundaries
1. CONTINENTAL PLATE COLLIDES W/ OCEANIC
PLATE
•Oceanic plate is denser and sinks under continental plate
•Area where ocean plate descends into mantle called
SUBDUCTION ZONE
•creates deep OCEAN TRENCH
•High temp & pressure cause subducting plate to melt
•Magma is less dense & rises which creates volcanoes along
plate boundary
EX: Andes Mtns - Nazca Plate subducts beneath
So.American Plate
EX: Cascade Mtns - Juan de Fuca Plate subducts beneath
No. Amer. Plate (Mt. St. Helens Volcano)
IRIS - Interactive Animations
IRIS - How do Earth’s tectonic
plates interact?
2. OCEANIC PLATE COLLIDES W/ ANOTHER
OCEANIC PLATE
One oceanic plate will bend & slide beneath the other
forming SUBDUCTION ZONE & OCEAN TRENCH
New magma produced rises to form a volcanic island arc
EX: Japan, Indonesia,
Philippines
3. CONTINENTAL PLATE COLLIDES W/
ANOTHER CONTINENTAL PLATE
•plates collide & crumple forming mountain ranges COLLISIONAL BOUNDARY
•No volcanic activity but earthquakes are common
EX: Himalayan Mtns Indian Plate colliding w/
Eurasian Plate
earthsci.org/teacher/basicgeol/ intro/contdontcoll.gif
Plates SLIDE past each other along faults
FAULT – break in Earth’s crust where movement has
occurred
EX: San Andreas Fault marks boundary btwn Pacific Plate
& North American Plate
Average rate of movement = ~5cm/yr
www.stanford.edu/.../news/gifsarch2/ san_andreas_text.jpg
www.exploratorium.edu/.../ images/faultaerial_sm.jpg
volcanoes.usgs.gov/Imgs/Jpg/Photoglossary/ fissure4_med.JPG
MAGMA AND LAVA
• Molten rock is slightly less dense than solid rock around it so it
RISES through fractures or makes its own path as it rises.
Rate of magma movement determined by SILICA CONTENT.
2 TYPES of magma/ lava
1. FELSIC/ GRANITIC – high silica content (>65%), thick, slow
moving (viscous)
2. MAFIC/ BASALTIC – low silica content (45-52%), thin, flow
easily; less viscous
GASES IN MAGMA
• Magma contains dissolved gases that are released as
magma erupts.
• Most important are WATER VAPOR, CO2, SO2.
• Amount of gas is BIG factor in kind of eruption.

As magma reaches surface, pressure is reduced allowing gases
dissolved in magma to come out of solution as bubbles.
 Bubbles can expand rapidly and even explode (soda bottle)
 Magma w/ lots of dissolved gases tends to produce more
explosive eruptions than magma with small amounts.
LAVA
AA – rough and jagged
PAHOEHOE – ropy, thin, has wrinkled appearance
volcano.und.nodak.edu/.../vwlessons/ lava_pics/pahoehoe.jpg
www.uhh.hawaii.edu/~csav/ images/aa.jpg
LAVA FRAGMENTS
• TEPHRA/PYROCLASTS – solid fragments of lava
produced in explosive eruptions.
• ASH – smallest, Lapilli, BOMBS and BLOCKS largest
• PYROCLASTIC FLOW – tephra combined w/ gases in an
explosive eruption forming a dense superheated cloud that
quickly travels downhill
• LAHAR – landslide or mudflow of pyroclastic material on
flank of volcano set off by eruption – Mt. St. Helens
astravel.rosnet.ru/adventure/ photo_kamch/Images/bomb.jpg
www.educeth.ch/stromboli/perm/ montserrat/icons/b09.jpg
www.geology.sdsu.edu/.../ lahars/laharmsh_s.jpg
Lahars at Mount Rainier?
During the past 10,000 years, there have been at least 60 different lahars
of various sizes originating from Mount Rainier (Hoblitt and others,
1995:5). There are now over 100,000 homes and over 200,000 Puget
Sound residents that work in buildings located on these deposits
(Krakauer, 1996:34). The largest of these lahars is the Osceola Mudflow
that occurred approximately 5,600 years ago and extends to the Port of
Tacoma including the areas now inhabited by the towns of Orting,
Buckley, Sumner, Puyallup, Enumclaw and Auburn (Hoblitt and others,
1995:5). A more recent lahar, the Electron Mudflow, originated as a
sector collapse from what is now known as the Sunset Amphitheater
around 600 years ago. The deposits left from the Electron Mudflow are
30 yards deep at the beginning of the Puget Sound lowland area and at
least 6 yards deep at the town of Orting (Hoblitt and others, 1995:5).
The following hazard map illustrates the areas at risk from future lahar
activity
www.uccs.edu/.../screen_ poster_lahar_haz1.jpg
TYPES OF ERUPTIONS
1.FISSURE ERUPTIONS
 Occur at long, narrow fractures in crust.
 Most occur on ocean floor
EX: along MORs – lava cools away from the fissure forming
pillow basalts

Typically flow out smoothly and fluidly b/c lava is
basaltic & gases escape easily
 On Land –lava may spread evenly over thousands of
sq. km. Known as flood basalts and can form large
basalt plateaus
EX: Columbia Plateau in Washington
• Deccan Plateau in India
volcanoes.usgs.gov/Imgs/Jpg/Photoglossary/ fissure4_med.JPG
2. VOLCANIC ERUPTIONS
VOLCANO – conical mountains formed around a vent
where lava, gases, and pyroclastic material are erupted.
Named after Vulcan – Roman God of Fire
 There are ~ 550 active volcanoes on earth – 60%
located in Pac. Ring of Fire
• Active = erupted in historic time
Ex – Kilauea, Mt. Etna, Mt. Pinatubo, Fujiyama, St.
Helens
 Numerous Dormant volcanoes – haven’t erupted
recently w/I last 100-200 years but may do so again
Ex. Vesuvius, Ranier, Shasta
 Many Extinct/ Inactive volcanoes – haven’t erupted in
recorded history and show no signs of doing so again
georoc.mpch-mainz.gwdg.de/ volcano.gif
mac.usgs.gov/.../volcanoes/ poster/posterfig4.jpg
upload.wikimedia.org/.../e/eb/Mt_St_Helens.JPG
2007
This page is <http://pubs.usgs.gov/pinatubo/>
Contact: Chris Newhall
Last updated 02.11.04
HOT SPOTS

Areas of volcanic activity in the middle of
lithospheric/ tectonic plates
 Basaltic Lava
• Form SHIELD CONES
Cause is unclear
 Believe it’s some kind of concentration of heat from
radioactive sources in asthenosphere
 Hot spot stays in same location and plate moves over
it
• chain of extinct volcanoes marking former position of
plate over hot spot
www.odp.usyd.edu.au/odp_CD/ volcis/images/hawaii.gif
www.astro.virginia.edu/.../ images/earth_hot_spot2.gif
EARTHQUAKES
www.geography.learnontheinternet.co.uk/ .../sanfran.jpg
EARTHQUAKE = shaking effect of Earth’s
crust caused by a release of energy
AFTERSHOCK – follow eqks as adjustments along
fault
SOME CAUSES:
• Erupting volcano, or magma moving in volcano
• Collapse of caverns or other very large structures
• Impact of meteorites
• **RELEASE OF STRESS built up btwn 2
lithospheric plates
SEISMIC WAVES
•
EQK generated waves that travel through Earth’s
interior in all directions
• Speed of wave depends on material it travels
through
2 TYPES OF SEISMIC WAVES
1. BODY WAVES – travel through interior
a. Primary (P-waves) – compressional/
longitudinal (squeeze & stretch)
b. Secondary (S-waves) – shear/ transverse (up &
down)
*slower than P waves
* DO NOT travel through fluid
Earth: Animation List
www.exploratorium.edu/.../ images/pswaves_sm.gif
FOCUS – point along fault where FIRST mvmnt
occurs (underground)
• Shallow focus eqks – focal depth <~70km – spreading
centers and transform boundaries
• Intermediate focus eqks – focal depth ~70-300 km
• Deep focus eqks – focal depth >~300 km – subduction
zones
EPICENTER – point ON EARTH’S SURFACE
directly above focus
Fault Motion Animations : IRIS
cse.ssl.berkeley.edu/img/earthquakes/ Epicenter.gif
MEASURING AN EARTHQUAKE
1. MAGNITUDE – strength of eqk measured
using the amplitude of largest eqk wave
*quantitative assessment determined by seismogram
RICHTER SCALE –developed by Charles Richter
in the 1940’s
•
Designed to measure amount of energy released by
eqk
2. INTENSITY - qualitative assessment of
damage done by eqk
MERCALLI INTENSITY SCALE
www.seismo.unr.edu/ftp/pub/louie/ class/100/richter-scale.GI
EARTHQUAKE RISK & PREDICTION
• ANY AREA that has experienced a damaging
eqk in the past is considered at risk of another
eqk in the future
• ~95% of eqks occur at or near plate boundaries
• ~5% occur at plate interiors
EARTHQUAKE DAMAGE
Building collapse – major causes are ground shaking and
foundation failure
GROUND SHAKING – result of the waves set in motion by eqk.
FOUNDATION FAILURE – result of ground shaking but different
 Soils may settle or become liquefied due to shaking eroding
building support and causing collapse
 First noticed w/ SF eqk. Bldgs w/ foundation on solid rk had
little damage while those on soft fill didn’t survive
 Liquifaction – water saturated sed loose cohesion and behave
as liquid (flow) caused bldgs in Nigata Japan to sink into
ground and collapse
college.hmco.com/.../resources/ geologylink/images/quake.gif
Tsunamis
– seismic sea waves are formed by earthquakes or
landslides
• tsunamis have long wavelengths, long periods and low
height
• compression of the wave’s energy into a smaller volume
upon approaching a coast causes a dramatic increase in
height
YouTube - Tsunami Incredible Video
Footages
Tsunami Visualizations
July 1993 Tsunami damage on Okushiri Island, Japan
In December 2004, a
great earthquake with a
magnitude of 9.15 on the
seafloor of the Pacific
Ocean created a large
tsunami that killed
168,000 people in
Indonesia. These photos
show the Banda Aceh
Shore near Gleebruk in
Indonesia on June 23,
2004 before the tsunami
(top) and on December
28, 2004 after it was
stuck by the tsunami
(bottom) (Concept 141B).
the rock cycle is the slowest of the earth’s cyclic processes. Rocks are recycled over millions
of years by three processes: erosion, melting, and metamorphism, which produce
sedimentary, igneous, and metamorphic rocks. Rock from any of these classes can be
converted to rock of either of the other two classes, or can be recycled within its own class.
Question: What are three ways in which the rock cycle benefits your lifestyle?
MINERAL – A solid, naturally occurring element or inorganic
compound with a regular internal crystalline structure
ROCK – solid combination of one or more minerals
Rocks are classified as one of three types based on how it formed.
1. Igneous – the majority of earth’s crust
2. Sedimentary – the majority of rocks at or near earth’s surface
3. Metamorphic
Rocks are constantly recycled through Earth’s rock cycle
ROCK ON!