Earthquakes and

Volcanoes

EarthquakesEarthquake – is the shaking and trembling that results from the sudden movement of part of the Earth’s crust.

Tsunamis – A giant sea wave produced by an earthquake.

Seismic WavesFocus – The point beneath the Earth’s surface where the rocks break and move, the underground origin of the earthquake.

Epicenter – The point directly above the focus, on the earth’s surface where the origin of an earthquake is above ground.

Faults- Once the elastic limit of rocks is passed, they break and move along

surfaces.• 3 types of faults are:

• Normal Fault- These form at divergent boundaries.

• Reverse Fault- These form at convergent boundaries.

• Strike-Slip Fault- These form at transform boundaries.

Seismic waves – earthquake waves. *Three types.

1. Primary waves (P-waves) – arrive at a given point before any other type of seismic wave. Will pass through solid, liquid and gas.(fastest of the three)

2. Secondary Waves (S-waves) – arrive at a given point after the P wave. (second fastest) Will only travel thru solids. Will NOT pass through liquids and gases thus creating a shadow zone.

3. Surface waves (L-waves) – slowest moving seismic

waves. Arrives last.

VolcanoesVolcano – the place in the Earth’s surface through which magma and other materials reach the surface.

Magma – rock that exists as a hot liquid deep within the earth.

Lava – is magma that reaches the Earth’s surface.

Vent – an opening from which lava erupts.

Crater – Steep walled depression around a volcano’s vent.

Hot Spot – Hot rock that is a result of unusually hot areas in the mantle and core where volcanoes form on the Earth’s surface. Hawaii is the result of a hot spot.

Lava flows• Basaltic – Is lava that contains a lot

of water and rich in iron and magnesium. Thin and quiet eruptions.

• Granitic - this lava contains very little water and is rich in silicon and aluminum. Thick heavy lava causing gases to trap underneath producing large violent eruptions. 

Composite Volcanoes – are made of alternating layers of rock particles and lava. Violent eruptions followed by quiet lava flows are the reasoning for the alternating layers.

Caldera – A roughly circular, steep-sided pit at the top of a volcanic cone whose diameter is at least three times its depth.

Andesitic - is a combination of both granitic and basaltic lava flows (quieter than granitic but more violent than basaltic).

Gas filled lava – This lava cools to form hole filled rock that has the appearance of a

sponge or loaf of bread. This rock type is typically light in weight. Pumice and scoria are examples of this type of igneous rock.

  

 

Liquefaction – Shaking up of wet soil making it unstable. This causes surface object to sink.

Earthquake preparedness – Tie down heavy objects, take objects off of high shelves. Build on an earthquake proof foundation. Have a plan and emergency items.

Seismograph – is an instrument that detects and measures seismic waves.Seismogram – is the record of waves.

(paper record)Seismologists – scientists who study

earthquakes.Richter scale – calculation of the strength

or magnitude of an earthquake.

For every 1 point rise 30 times the energy is released.

Magnitude - Height of a line traced on a seismogram.

Tephra – bits of rock or solidified lava dropped from the air.

Volcanic Dust – Is fragments of rock that are blown into the air during a volcanic eruption. (very

small particles)

Volcanic Ash – Is particles blown into the air from a volcano that are bigger than volcanic dust yet smaller than anything else.

• Volcanic Bombs – Are large rock particles that are blown out during a volcanic eruption.

• Volcanic cinders – are smaller volcanic bombs.

• Cinder cone volcano – Volcanoes made mostly of cinders and other rock particles that have been blown into the air. Narrow bases with steep sides due to loosely arranged cinder type eruptions.

Shield volcano – Volcanoes composed of quiet lava flows. Gently sloping sides with very wide base.

Dike –

Batholith –

Sill -

Dormant – (sleeping) has erupted but not in modern time.

Extinct – Not known to have erupted in recorded time. Usually weathered down to base.

Active – well, it is active in modern time.

ZONES

Ring of fire – is the zone of active earthquakes and volcanoes due to very active tectonic plate movement.

Mid-Atlantic ridge – chain of ridges caused by sea floor spreading.