Effects of Plate Tectonics Volcanoes and Earthquakes

Types of Eruptions Violent and explosive Quiet and flowing The type of eruption depends on trapped gases and magma composition!

Volcanoes A point on the earth’s surface where magma (molten rock) reaches the surface Vent—opening through which lava erupts Crater—large depression surrounding vent

Magma Composition Two types: –Basaltic – less silica and very fluid; produces quiet eruptions –Granitic – lots of silica, high water vapor content, and very thick; produces very violent eruptions

Trapped Gases Water vapor and carbon dioxide are trapped in magma At low pressure, they escape quietly when they reach the surface At high pressure, they escape violently when they reach the surface

So… The magma composition AND the trapped gases will determine what type of volcano you will get! Violent eruptions produce lots of ash, while quiet eruptions produce lots of lava.

Shield Volcano Formed by quiet eruptions Basaltic lava builds up in flat layers (many lava layers) Broad, gently sloping sides Ex: Hawaiian Islands

Cinder Cone Volcano Caused by explosive eruptions Granitic lava thrown high into the air falls back and piles up around the vent. Made up of volcanic fragments such as glass, ash, rock Lava cools into different sizes of volcanic material called tephra. Steep-sided, loose slopes, usually small

Composite Volcano Layers of volcanic fragments alternate with lava (A mix of the other two types) Quiet or violent Basaltic or granitic Steep or gentle slopes. Very large Layered or tephra

: The rise of Pu`u `O`o episodic lava fountains build massive cone

disasters/earthquakes/earthquake-montage.html quake-video.php

Earthquakes! An earthquake is the result of a sudden release of stored energy in the Earth's crust that creates seismic waves. When two plates slip past one another or collide, different kinds of stress result.

Stress—3 types Compression— stress that decreases volume of rock and results in a reverse fault Tension—stress that pulls rock apart Shearing—stress that causes rock to twist

Reverse fault: hanging wall moves up

Normal fault: hanging wall moves down

Strike slip fault: hanging wall slides past

Earthquakes Focus—point below Earth’s surface where earthquake originates Epicenter—point on Earth’s surface directly above focus Fault—break or fracture of rock at Earth’s surface where movement can occur Stress—force put upon rock

Seismograph

Seismic Waves There are 3 different types –P waves –S waves –L waves They have helped scientists learn more about the interior of the Earth!

Seismic waves P-waves— compression waves P-waves— compression waves –Move through liquid –Fastest waves

S-waves S-waves –Move perpendicular to wave direction –Do not move through liquid –Slower than P- waves

L-Waves (Surface Waves) L-Waves (Surface Waves) –Are the slowest moving waves –Cause the surface to rise and fall like ocean waves –Also cause the most damage!

Review Quiz! 1) Name the 3 types of volcanoes! 2) The large depression surrounding the vent is called the ________. 3) What is molten rock called that reaches the Earth’s surface? 4) What type of lava contains less silica, is very fluid, and produces quiet eruptions?

5) Gases trapped at ______ pressure cause violent eruptions. 6) What type of eruption releases a lot of ash? 7) This type of volcano is formed from quiet eruptions from layers of basaltic magma. 8) This type of volcano is formed from violent eruptions and lots of volcanic fragments.

9) This type of volcano can cause either violent or quiet eruptions. 10) What is the scale that measures earthquake intensity? 11) Name the 3 types of seismic waves! 12) Which is the slowest seismic wave? 13) Of the 3 seismic waves, which one can move through liquids?

14) Which seismic wave causes the most damage? 15) The ________ is the point below Earth’s surface where the earthquake originates. 16) The point on Earth’s surface directly above the focus is called the ________. 17) A ________ is a break or fracture of rock at Earth’s surface where movement can occur.

Answers! 1) Shield; Composite; Cinder Cone 2) Crater 3) Lava 4) Basaltic 5) High 6) Cinder Cone 7) Shield 8) Cinder

9) Composite 10) Richter Scale 11) P waves; S waves; L waves 12) L waves 13) P waves 14) L waves 15) Focus 16) Epicenter 17) Fault