Unit 6: Earth Shaped from the Outside in

Unit 6: Earth Shaped from the

Outside inCycle 18: Volcanism & earthquakes

Cycle 19: Plate TectonicsCycle 20: Weathering & Erosion

Connection to last unit…

To deeply understand the processes that create rocks and minerals such as volcanism, weathering, pressue, etc. need more information about where in the world these things happen

Connections beyond…

Why learn it? So inherently cool! So dangerous, need to be prepared So relevent, in the news eery day

impacting people around the world

Class Opener Do mapping activity Are all the earthquakes

and volcanoes evenly spaced randomly across earth’s surface?

Why do earthquakes and volcanoes occur where they do?

Volcanoes &Volcanism

Volcanoes=the cone structure volcanism=movement of magma out of the earth

Volcanism is caused by solid rock melting. Liquid rock is less dense and therefor rises Review: kinetic molecular theory of matter

What 3 things cause rock to melt and

rise? Increasing temperature Adding water Decreasing pressure

Along plate boundaries & intra-plate areas Ring of Fire Mid-Ocean Ridge Hot Spots Volcanic Arcs

Divergent Plate Boundary Volcanism

Convergent Subduction Plate Boundary Volcanism

Intra-Plate Volcanism (hotspots)

•Convergent Subduction Volcanism– Plates are colliding with each other

and subducting. lithosphere is being melted

– Volcanism due to increased temps, water

•Divergent Volcanism– Plates are ripping apart– Volcanism due to

melting of asthenosphere due to less pressure from above

•Intraplate Hotspot Volcanism

– In middle of plates– Hot spot in mantle– plume rises towards the

surface due to density difference

Volcanic Structures As eruptive materials pile up at an opening a

“volcano” formsShieldCompositeCinder

Shield Volcano Shield Volcanco

-Low angle slopes of 1-10Largest volcano-Hawaii, Iceland-Generally on ocean floor-”quiet” eruption-made of basalt lava flows, no ash or pyroclastics

-basaltic magma, low gas trapping

Steeper slopes 10-25, taller than cinder cones. Smaller in height and width than shield volcanoes

Cascades (Mt. St. Helens), Andes

Volcanoes on continents over ocean-land subduction zones

Alternating Explosive/quiet eruptions

Built up by alternating layers of lava and pyroclastics

Built over tens to hundreds of thousands of years

Andesitic (or Granitic) composition magma, gas rich

Composite Cone/Stratovolcano

Smallest volcanic features have large craters with steep slopes of 30-40

Paricutin, MexicoGenerally forms on continentsExplosive eruptionsBuilt of pyroclastics (tephra/cinders) not lava

flows.Generally short lived eruptions - weeks to a

few years until the magma is degassed, then it solidifies in the pipe and flows form from the base

Cinder Cones

Paricutin, Mexico, cinder cone soon after its birth in 1943 in a Mexican cornfield.

What determines the shape, eruption

type… What determines what kind of volcano forms?

The eruptive materials (lava vs. pyroclastics) What determines what kind of eruptive materials occur?

Type of eruption (explosive vs. quiet) What determines what kind of eruption occurs?

The amount of pressure build up from trapped gas especially

What determines the gas content and composition of the magma? What type of rocks are being melted, ocean floor,

continental, both, asthenosphere, LOCATION

Warning signs of impending eruption

Earthquakes increase in frequency and strength

Ash and gas increases Bulging of volcano side

Dangers Pyroclastics: breathing, hit by it Lahars/mudflows: concrete flood Poisenous hot gases: can’t breath Pyroclastic flows: instant incineration

700km/hr

(450mph)

Deaths 1600-1982

Earth’s Layers Formed during early precambrian when earth was liquid rock

all over 3 layers based on differences in composition

Crust, mantle, core 5 layers based on differences in “stiffness/fluidity” of material

Lithosphere, asthenosphere, lower mantle, outer core, inner core

How do we know? Earthquakes! Seismic waves travel faster in denser materials. S-waves only travel through solids (both rigid and plastic) Inferences based on overall density calculations for earth,

observations of surface materials, lava, and meteorites

What is an Earthquake? Definition: sudden, strong shaking of the

earth’s crust caused by release of energy Usually happens along faults

Movement of rigid solid crust causes stress in rocks

Rocks bend/stretch/compress/distort their shape

Breaking point reached and rocks release energy and move along fault

Go back to original “unbent” shape

Can only occur in rigid solids of crust

What are seismic waves?

Body wavesP waves Primary wave Focus Faster Arrive first Push-pull waves (compress/stretch rock, no

shape change) Move through solids, liquids and gases

S waves Secondary Focus Slower Arrive Second Up and down waves (change shape of rock) Only move through solids

How do we measure earthquakes?

Locating the epicenter of an earthquake

The farther the station is from the epicenter, the greater the time is between the arrival of primary and secondary waves

Need 3 stations

Travel Time Graph1. How long does it take the S & P

wave each to travel 1000 mi? 2000 mi?

2. How much sooner will the P wave arrive at a seisograph station 1000 mi away from the earthquake location? 2000mi?

3. What is the general relationship between difference in arrival time between P & S wave and distance?

4. This graph can help geologists identify distance to earthquake epicenter but not… Direction!

Earthquake dangers Falling objects Collapsing buildings Collapsing bridges, tunnels, etc. Fires (caused by broken gas lines etc.) Tsunamis near coast Interuption in medical and other

emergency services due to debris and road closures

Safety Precautions Inside:

Drop, cover, hold on! Protect your head from falling objects, windows etc.

Don’t try to get outside during shaking Be prepared for aftershocks

Preparing your home for EQ safety Bolt bookcases etc. to wall No heavy objects above bed Know how to turn off gas & water

Caught at the coast: Did the tide go out quickly? If you are seeing more of the

bottom of the ocean than you should… Get to higher ground!

Earthquake frequency and cause Earthquakes in New England? What causes earthquakes Most frequently at plate boundaries but

can happen anywhere in plate, especially if there are faults already in rock