Geology 3

What comes out of a volcano

1. lava (molten rock) 2. Pyroclastic 3. Gas

3 types of lava

a. Basaltic Lava b. Rhyolitic Lava c. Andesitic Lava

1950-60 advances: Bathymetry

- Mapping of the seafloor by using Echo Sounder to get a detailed look of the sea floor - For Submarines

3 Steps to Figuring out if there was a quake

1. Determine how long the S-wave arrived after the P-wave -Recall that the P-wave travels faster than the S-wave. -Therefore, the P-wave arrives before the S-wave. -Therefore, the further you are from the epicenter, the more time between when the P-wave and S-wave arrive. 2. Convert the time between when the S-wave arrived and the P-wave arrived to a distance -This is done using a travel-time curve. 3. Find the exact location using triangulation

1950-60 advances: Paleomagnetism

- Understanding Earth's magnetic field, and its behavior in the past Magnetic Field is changing 1. True north (i.e., the north pole) and magnetic north do not match up. 2. Magnetic north moves around. 3. Earth's magnetic poles "flip" about every 500,000 years. Magnetite crystals are little magnets, and will orient themselves with Earth's magnetic field while the lava is fluid enough for the crystal to move which causes Magnetic Anomalies ~Positive magnetic anomaly: magnetic field is a little stronger than normal ~Negative magnetic anomaly: magnetic field is a little weaker than normal STudy

Liquefaction

-If loose material is saturated with water, shaking may cause liquefaction -Water in the soil is squeezed upwards, and it causes the soil to liquefy

Basaltic Lava

-Low in silica (about 50%) - low viscosity (very fluid) - fast flowing - can flow far (90 miles from the source) 2 types of Basaltic Lava 1. Pahoehoe Very fluid, forms a smooth surface that wrinkles as it flows, giving it a ropy appearance. Flows quickly, at rates of 10-300 ft/hour - Killed a lot of people in Congo because lava was flowing 20mph 2. Aa Has a rough, sharp surface made of blocks of lava Flow slower than pahoehoe, at rates of 15-150 feet/hour.

Aftershocks

-Small quakes that follow the main quake -Usually very common at first, but become less common with time Probably due to the fault setting back into place after it moved.

Pyroclastics

-Solid fragments erupted from the volcano -Range in size from a fine powder to pieces of rock the size of a bus. Created in 2 ways: 1. Lava is thrown into air and it solidifies 2. An explosive eruption pulverizes rock and throws it into the air

Earth's Internal Heat

-Temperature at the core-mantle boundary is about 3500-4500°C. -Estimated to be 6700°C at the center of Earth. Source of heat: comes from radioactive decay of isotopes of Uranium, Thorium, and Potassium

Evidence of Continental Drift

1. Continental Fit - The continents look as though they would fit together like pieces of a jigsaw puzzle if the continents were forced together 2. Past glaciations - When glaciers grow during ice ages they leave evidence behind that tells scientists they were there. - Striations: scratches in the rock which are worn into the rock as the glacier passes over it. - Glaciations that were found in old rocks were continuous to each other when the Continents were pushed together 3. Other Climatic Data - Climatic data from different parts of the world don't match well with where the continents are today. - Coal is Siberia but Coal is formed in warm tropical environments and Siberia is not tropical 4. Fossils -Different continents contain different species that are unique to that continent. But different continents contained the same fossils - When continents were joined together the organism would occur over a single range 5. Matching Geologic Units and Mountain Ranges - Found similar geologic units - Found that mountain ranges would connect from different parts of the world if they weren't ripped apart

Earth's interior consists of 3 main layers:

1. Core - about the side of the moon (3500km) - Iron and Nickle - 7000 C SUPERHOT - Made of TWO layers: ~inner core: solid ~ outer core: molten 2. Mantle - 2900 km thick - 82% of Earths Volume - upper and lower mantle - lithosphere / asthenoshphere 3. Crust - made up of TWO types of plates 1.Continental Plates ~ thick 35-70 km inches in thickness, low density (floats), made of granite, old ~ thick and float 2. Oceanic Plates ~ thin 2-15 km, high density, young, made of Basalt. ~thin and sink

3 Types of Plate Boundaries

1. Divergent plate boundaries - plates pull apart - crust is created here 2. Convergent Plate boundaries - plates push together - crust is destroyed 3. Transform fault boundaries -Plates slide past each other -Crust is neither created nor destroyed here

Predicting Volcanic Eruptions: Short term

1. Earthquakes Magma working its way up to the surface will crack apart rock as it rises, creating small earthquakes (M2-4). These usually occur as swarms, where dozens or hundreds will occur in a short time. Usually become more frequent when an eruption is close. 2. Changes in the shape of the Volcano Rising magma will usually create a bulge in the volcano. Satellite observations and laser surveys can detect small changes in the shape of the volcano. 3. Changes in Gas Emissions Changes in the amount of, and types of gases being given off by the volcano will commonly signal and eruption. Typically, the amount of gas being emitted by the volcano will increase prior to an eruption. 4. Changes in Hot Springs Hot springs may become hotter prior to an eruption. In addition, the chemistry of the water in the hot springs may change before an eruption.

4 Factors that do structural damage attributable to Earth Quake vibrations

1. Intensity of Shaking Stronger shaking = more damage Shaking is about the same everywhere within 12-30 miles of the epicenter, but then rapidly decreases further away. 2. Duration of Shaking Longer shaking = more damage 3. Design of the structure Wood-framed houses, and steel-frame buildings survive much better than those made of unreinforced brick. Stronger, inflexible buildings suffer more damage than those that can more with the quake. 4. Foundation Material Soft sediment tends to amplify shaking and make it worse. So houses built on loose soil will be subjected to much more shaking than those on solid rock. This can cause damage far from the epicenter.

2 Types of Divergent Boundaries

1. Ocean-Ocean: Two ocean plates pull apart. As the plates pull apart, they create a crack called a mid-ocean ridge. New crust is created as magma rises to fill the crack, and then cools. 2. Continent-continent: Two continental plates pull apart. Creates a large crack on land called a rift valley Sea water will fill into rift valley making a crack Eventually continent will be completely split

Types of Volcanoes

1. Shield Volcano - largest volcanoes - have gentle sloping sides - forms from basaltic lava - mellow eruptions (Largest volcano on Earth is Mauna Loa [6 miles high], Largest volcano in Solar system is Olympus Mons [15 miles high] found on mars) 2. Cinder Cone - Smallest volcanos - have steep sides - made of pyroclastic erupted form the volcano - forms from basaltic lava - mellow eruptions not as mellow as shield - may have lava flow towards the end of an eruption - Usually only erupt once 3. Composite Cone - Called a Stratovolcano - Medium Sized - Have sleep sides - Made of layers of lava and ash - Form from Andesitic lava - most violent volcanoes - Eruptions typically begin with ash eruptions, and are followed later by lava flows. - Two especially dangerous and deadly processes associated with cinder cone eruptions are pyroclastic flows and lahars. 4. Lava Dome Form from rhyolitic lava Lava is so viscous, it can barely flow, so it tends to build up as a blob of lava Small lava domes commonly form in the crater of a composite cone near the end of an eruption.

What affects viscosity

1. Temperature: hotter = more fluid 2. Composition of the magma The amount of silica in the magma is especially important. More silica = more thick and pasty magma

3 Types Convergent plate boundaries

1.Ocean-ocean When 2 ocean plates collide, one of the plates is forced down (subducted) into the mantle. Subduction creates a deep trough on the seafloor, called a trench. As the subducting plate gets pushed deeper into the mantle it gets heated and melts The magma rises to the surface and creates a volcanic island chain 2. Ocean- continent Ocean plates will sink under the continent when they collide because they are denser This makes a deep ocean trench which melts the ocean plates and produced magma which rises to form a volcanic mountain chain 3. Continent- continent Since continental plates have a low density, they crumble and form mountain ranges instead of sinking. no volcanos

Types of Seismic waves

2 Types 1. Body waves: Travel through Earth's interior 2. Surface waves: travel along Earth's surface.

Rift Valley

2 continental plates pull apart and create a large crack

Mantle

2900 thick and make up 82% of the Earth's volume Solid rocky layer Made up off green rock called Peridotite Made up off 3 parts

Earth Quake

An earthquake is the vibration of Earth produced by the rapid release of energy -Typically due to movement of rock along either side of a fault -Most occur along plate boundaries where plates are moving past each other -30,000 earth quake a year but only 75 are significant - longer the time between earthquakes the bigger they are because there's more time for stress to build up to higher levels

Sizes of Pyroclastics

Ash: fine powder Cinders: sand-sized Lapilli: bead to walnut-sized Bomb: Blob of lava erupted from the volcano that solidifies in midair - usually football shape Block: large piece of rock blown from an explosive eruption - can be size of a bus and can be thrown several miles

Crust

Broken into large pieces called plates 1. Continental Plates: Thick: 35-70 km in thickness Low Density: 2.7g/cm3 Old: average age = 3.5 billion years old Made of granite. 2. Oceanic Plates: Thin: 3-15 km in thickness High Density: 3.0g/cm3 Young: no older than 180 million years old Made of basalt.

Mid-ocean Ridge

Unknown at first but made know by Bathymetry - Long volcanic mountain chains that extend through all of the world's oceans.

Types of Surface waves

Caused by P-waves hitting Earth's surface from below 2 types of surface waves: 1. Love wave Side-to-side motion 2. Rayleigh wave Up and down motion more destructive (this causes the damage)

2 types of Crust

Continental crust made of mainly granite very old 3.5 billion thick 35-70 km Oceanic Crust made of basalt oldest ocean 180 mill thin 3-15km

Shallow focus occur mostly along the oceanic ridge system. Why?

Crust is thinner there as the plates pull apart.

1950-60 advances: Radiometric Dating

Dating of rocks using radioactivity Revealed 2 interesting things: 1. Average age of the continents is 3.5 billion years old. -Oldest ocean rock is 180 million years old. 2. Ocean floor rocks are new at mid-ocean ridges and get older the further you get from the ridge.

Kimberlite Pipe

Deep volcanoes that tap the upper mantle and bring pieces of it to the surface Part of mantle

What makes volcanic eruptions explosive?

Gas. If the lava is thick and pasty, it won't let gas escape, and it will build up to explosive levels.

Trench

Unknown at first but made know by Bathymetry - elongate troughs where the water depth reaches 8-12 km deep (versus about 3-4 km for the majority ocean)

Theory of Plate Tectonics

Earth's crust is divided up into several large pieces called plates. - moving around 1-5 cm a year -Where plates pull apart, crust is created (Hess' seafloor spreading idea) -Where plates push together, crust is destroyed. - the action happens along the edges of plates (plate boundaries can be seen when the global pattern of earthquakes (and volcanoes))

What causes the plates to move?

Earth's internal heat. As mentioned earlier, the Earth is very hot inside (nearly 7000°C). When mantle material is heated by the core, this material rises. The mantle material will rise until it reaches the bottom of the crust, where it will begin to cool. When it gets cold enough, it sinks back down towards the core. How fast does this material move? About 1-5 cm/year (about as fast as your fingernails grow) How do we know? We can use satellites to measure plate movement, and we believe the mantle flows at about the same rate.

geothermal gradient

Earth's temperature gradually increases with an increase in depth at a rate

What causes Earth's tectonics plates to move? Approximately how fast do the plates move?

Earths internal heat and 1-5 centimeter per year

Seismic waves

Energy released at the focus radiates out in all directions in the form of seismic waves.

Andesitic Lava

Medium in silica (about 60%) Middle Viscosity Lava flows Typically have a smooth blocky surface

Gas

Gases make up 1-6% of lavas. If these gases build up, they can create explosive eruptions. Gas dissolves in the lava like beer or soda If the gas is trapped, however, it will build up to explosive levels, and may completely blast out part of the volcano when it erupts. look at power point

Long-term earthquake prediction

Gives the probability of a certain magnitude earthquake Tries to determine how often quakes of a given size occur along a fault Does this using historical records -If a quake occurs every 20 years along a part of the San Andreas fault, and its been 30 years since the last one, then chances are good that a quake will happen soon.

1950-60 advances: Geopoetry

Harry Hess - Mid Ocean Ridges are giant cracks in Earths Crust are being pulled apart as the ocean spreads - Magma comes up from below and fills in the crack, making new seafloor when it solidifies. - Idea was rejected because it basically implied that the Earth can get larger which is false

Rhyolitic Lava

High in silica (about 70%) - High viscosity, very thick and pasty. - Flow so slowly you might not even see it move - Smooth, blocky surface - usually flow a mile or two from the crater - may not even flow out of the crater and forms a pile of lava called a lava dome - lava domes = hella dangerous

Hot Spot

Hot spots (sometimes called mantle plumes) are hot areas in the mantle that rise towards the surface and produce magma as they get close to the surface, and commonly produce large volcanoes. Hot spots begin deep within the Earth, perhaps as far down as the boundary between the core and the mantle. They last for millions to 10's of millions of years. The hot spot doesn't move, but the crust above the hot spot does. This results in a line of volcanoes being burned into the crust, with only the volcano directly over the hot spot being active. Because hot spots remain in place they can be used to tell the direction of plate motion in the past, as well as how fast the plates were moving.

Richter Magnitude

Introduced by Charles Richter in 1935 Based on the amplitude of the largest seismic wave recorded Is only really effective for nearby earthquakes (local earthquakes) Determines magnitude of an earthquake by measuring how much movement occurred along a fault. More movement = greater magnitude Is measured by using seismograms, as well as going out to the fault and measuring how much displacement occurred This provides the most accurate way of measuring size since seismogram calculations can be verified by field measurements This is also why magnitudes of big quakes change over time. This is the standard way of measuring quake size

What is the core made of? What are the 2 layers of the upper mantle, and how do they differ?

Iron and Nickle Lithosphere is solid upper athso below and taffy like

Core

Larger than the planet mar and about the size of the moon High pressure (million times atmospheric pressure) 6700 Degrees Celsius (Hotter than sun)

3 Parts of Mantle

Lithosphere or uppermost mantle and crust Asthenosphere or upper mantle Mesosphere or lower mantle

Magnitude

Measures the amount of energy released by the earthquake - Logarithmic scale (increase by 1 is actually 10)

seismographs

Measures the earth quakes

What did mapping of the seafloor reveal? What did radiometric dating reveal?

Mid ocean ridges trenches Continent is older than ocean

Lahars

Mudflow created by a volcano. Volcano eruption melts glaciers at the top of the glacier, and sends a wall of water down the side of the volcano Heavy rainfall mixes with ash, creating a mudflow

What are the 5 lines of evidence Alfred Wegener used to explain his theory of continental drift? Was his theory accepted when he originally presented it?

No it was not.

What are the 2 types of plates and how do they differ with respect to composition, density, and thickness?

Ocean is denier, basalt, thin. Continental granite, thick, less dense.

Fire

Often the most destructive part of an earthquake. Fires are fed by broken gas lines Water lines are also broken

Asthenosphere

One layer of the mantle Solid rock, but under high pressure Similar to taffy

Lithosphere

One layer of the mantle Solid, rigid rock Includes the crust

Earth Quake Depth

Originate at depths ranging from 5 to nearly 700 kilometers Earthquake depths are shallowest nearest trenches They get deeper away from the trench This is due to an ocean plate diving down under another plate.

Two parts of the core

Outer Core -liquid outer layer Inner Core - solid Inner sphere Both made of iron and 5-10% nickel They know this because Astronomers calculate the density around 11 and iron is 11 - Iron is common in the solar system (50% of all meteorites) The core likely formed early in Earth's history when the planet was still molten

Define plate tectonics. How do scientists determine the location of plate boundaries?

Plates are constantly moving

Continental Drift

Published in The Origin of the Continents and Oceans in 1915 by Alfred Wegener (German Meteorologist) - Idea that continents were once joined into a single landmass that Wegener named PANGAEA

Short-term earthquake prediction

Relies on the Elastic rebound theory As stress builds up along a fault, the rocks bend first, and they they break. If you can see evidence of bending, this might tell you that an earthquake is coming. Scientists have looked for evidence of bending of rock along the San Andreas fault using satellites and lasers to note tiny changes (as small as 1 mm) in elevation along the fault. This hasn't been real successful. -Some large earthquakes will also be preceded by smaller quakes called foreshocks, that have been suggested as a way to predict a quake Not all big quakes have foreshocks before them Sometimes small quakes are called foreshocks, but no big quake follows them.

Seiches

Shaking of the ground causes water to slosh back and forth as a wave called a seiche.

Pyroclastic Flows

Sometimes also called by their French name, nuée ardentes (which means "glowing cloud") Hot flow of ash and gas that moves quickly down the side of a volcano. Denser than air, so they hug the ground as they travel. Hot! (up to 1200°C) Fast: speeds up to 120 mph One famous pyroclastic flow occurred in 1902 from Mount Pelée, a volcano on the Caribbean island of Martinique. (1 survived out of 28,000 and flow only lasted 5 minutes)

What leads to the development of volcanoes at convergent plate boundaries? At divergent plate boundaries?

The less dense one will sink and melt making a volcano Divergent one moves apart and magma comes up

Earth's Magnetic Field

The origin is controversial - most think its due to friction between Earth's outer core and mantle -The core and mantle rotate at different speeds, causing friction, and creating static electricity. -This electricity then sets up a magnetic field.

Epicenter

The point on Earth's surface directly above the focus

Focus

The point where an earthquake begins

Why was continental drift rejected?

The reason was because Wegener could not : -Provide a mechanism to split apart continents -Explain how the continents plow through the solid rock of the ocean floor.

Lava Tubes

The top of the Pahoehoe flow will commonly solidify, but lava will continue to flow through a cave-like system of lava tubes beneath the hardened surface.

Viscosity

The viscosity of the lava make volcanos erupt differently each time. Viscosity means how thick a fluid is.

Describe and draw each of the plate boundaries discusses in class. What types of features form at each plate boundary? Give a specific geographic example of each type of plate boundary.

They use earth quakes and volcanos SPECIFIC EXAMPLES

Isostacy

This concept of "floating" plates - Ocean plates will sink lower into the asthenosphere - Continental plates will float a little high on the asthenosphere

Almost all deep-focus earthquakes occur in the Pacific region, particularly near deep-ocean trenches. Why?

This is due to the plates colliding along convergent plate boundaries and sinking into the mantle

Tsunami

Tsunamis, or seismic sea waves Result from the seafloor suddenly being dropped or lifted upwards during an earthquake. Difficult to detect Height is usually < 1 meter in the open ocean Once they enter shallow water they can grow to heights of 30 meters (100 feet) Travel at speeds of 400 mph. Detection is difficult, so usually a tsunami warning goes out after a major earthquake, and scientists look to see if areas closer to the quake have been hit by tsunami. If so, then they evacuate areas further away.

Predicting Volcanic Eruptions: Long term

We can get an idea of how often a volcano erupts by figuring out how often it has erupted in the past, and when it last erupted.

What is a hot spot? How do they form? What can hot spots tell us about past plate motion?

What direction it was moving and how fast it was moving

Fault Creep

a process Plates are always moving, and, as a result, slide past each other. In rare cases, motion is steady, and the plates move almost constantly on either side of the fault

Intensity

measures how the quake affected people and buildings.

Why were the 1950's and 1960's a time of great scientific achievement?

~ Wegener Died, but his idea came back to life because of Scientific advances in 1950-60 COLD WAR

Types of Body Waves

~p-waves (primary, fastest of all earthquake waves, compressional wave like a spring) ~s-waves (after the pwave secondary, a little slower, shearing wave like an ocean wave)