Tectonic Forces and Natural Disasters I

3rd lecture (9/9)

Plate Tectonics

Movement of lithospheric plates driven by heat from Earth’s core

• Earthquake activity reveals plate boundary locations

Ridge Push

The force of hot magma rising to the surface beneath the ridge

Slab Pull

The slab portion of a plate accelerates plate movement by pulling the plate deeper into the mantle

Mantle Drag

Movement of a plate caused by friction between moving asthenosphere and the lithosphere

Moving Plates Cons (2)

• Cause earthquakes which cause tsunamis 

• Creates volcanoes

Moving Plates Pros (3)

• Resulting volcanic ash creates fertile soil 

• Builds land 

• Cycles carbon from the asthenosphere and the lithosphere 

Faults

A break in the earth’s crust

Normal Faults

The block above the fault has moved downward relative to the block below

Strike-strip Faults

When tectonic plates move past each other horizontally.

Reverse Faults

The upper block, above the fault plane, moves up and over the lower block

Overthrust Faults

A thrust fault with a low dip and large slip

• a thrust fault in which the hanging wall was the one that moved (underthrust)

Grabens

A crustal block dropped down between two normal faults

Horst

A crustal block pushed up between two normal faults

Fault Scarps

small step or offset on the ground surface where one side of a fault has moved up

How can earthquakes be helpful?

Earthquake activity reveals plate boundary locations

Magnitude

The amount of energy released by an earthquake

Focus

Location where a fault slipped

Epicenter

Directly above where a fault slipped to produce an earthquake

How are epicenters calculated?

Triangulating readings from three different reading centers across the country (A, B, and C) & using the difference in travel times for P and S heat waves

Human Induced Earthquakes occurr by…(2)

• Petroleum (oil) is found w/ sedimentary rocks 

• Drilling & fracking at shale (rock) oil fields create earthquakes 

“Tsunami” translates to...

Harbor Wave

How do tsunamis form?

• Underwater earthquakes. 

• Volcanic eruptions. 

• Landslides. 

• Asteroids

How are volcanoes formed?

Lava-Magma that spills onto the surface of Earth’s crust

Volcanic gasses include…

Water vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), & hydrogen sulfide (H2S)

Shield Volcanoes

Broad & domed; LARGEST VOLCANOES

• Built as magma travels up from the magma chamber and through the volcanic vent

Stratovolcanoes

AKA composite volcanoes; Cone shaped; Steep; Made of lava & pyroclasts

Pyroclasts

Any fragmented solid material that is ejected from a volcano

Ash

Pulvarized rock + solidifed lava

Cinder Cone

Small, cone shaped w/ pyroclasts; Symmetrical, small

Lava Dome

Dome shaped; thick lava that piles around a volcanic vent & solidifies

• REALLY small; Can form on or cap shield and stratovolcanoes

Mafic Lava (temp, vicosity, forms…)

1800-2200 degrees; low viscosity and gas content; forms basalt

Intermediate Lava (temp, vicosity, forms…)

1500-1800 degrees; intermediate viscosity & gas content; forms andesite

Felsic Lava

1200-1500 degrees; high viscosity & gas content; forms rhyolite

Mt. Vesuvius (AD 79) 

• Stratovolcano; rich volcanic soil good for growing grapes

• Named for Herules aka Ves

What caused Mt. Vesuvius & the 3,000+ deaths thereafter

• Caused by the collision of the African & European plates

• Poisonous gases carbon dioxide (CO2) and hydrogen chloride (HCl) escaped from the volcanic vent