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The Structure of Earth
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
4. CRUSTOutermost 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)
Crust/Mantle Boundary discovered 1909 = MOHO
HOW DO WE KNOW??
Seismic (Earthquake) wave data
Rock Core samples - GLOMAR CHALLENGER
Drilling Vessel GLOMAR CHALLENGER, Deep Sea Drilling Project, SIO, 1968DSDP 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
Fig. 14-3, p. 346
Spreading center
Ocean trench
Plate movement
Subduction zone Oceanic crust Oceanic crust
Continental crust
Continental crust
Material cools as it reaches
the outer mantle
Cold dense material falls back through
mantle
Hot material rising
through the mantle
Mantle convection
cell
Two plates move towards each other. One is subducted back into the mantle on a falling convection current.
Mantle
Hot outer core Inner
core
Plate movement
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
RIFT VALLEY
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 - How do Earth’s tectonic plates interact?IRIS - Interactive Animations
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.exploratorium.edu/.../ images/faultaerial_sm.jpg
www.stanford.edu/.../news/gifsarch2/ san_andreas_text.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/ lava1. 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.
LAVAAA – rough and jaggedPAHOEHOE – 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
www.educeth.ch/stromboli/perm/ montserrat/icons/b09.jpg astravel.rosnet.ru/adventure/ photo_kamch/Images/bomb.jpg
www.geology.sdsu.edu/.../ lahars/laharmsh_s.jpg
www.uccs.edu/.../screen_ poster_lahar_haz1.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
TYPES OF ERUPTIONS1.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 timeEx – 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 againEx. Vesuvius, Ranier, Shasta Many Extinct/ Inactive volcanoes – haven’t erupted in
recorded history and show no signs of doing so again
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 NewhallLast 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
through2 TYPES OF SEISMIC WAVES1. 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
cse.ssl.berkeley.edu/img/earthquakes/ Epicenter.gif
Fault Motion Animations : IRIS
MEASURING AN EARTHQUAKE1. 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
Tsunami Visualizations
YouTube - Tsunami - Incredible Video Footages
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 14-1B).
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!
