Unit 6: Earth Shaped from the Outside in Cycle 18: Volcanism & earthquakes Cycle 19: Plate Tectonics Cycle 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

Convergent Subduction Plate Boundary Volcanism Divergent Plate Boundary Volcanism Along plate boundaries & intra-plate areas Ring of Fire Mid-Ocean Ridge Hot Spots Volcanic Arcs 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 Shield Composite Cinder As eruptive materials pile up at an opening a “volcano” forms Shield Composite Cinder

Shield Volcano Shield Volcanco -Low angle slopes of 1-10 Largest volcano -Hawaii, Iceland -Generally on ocean floor -”quiet” eruption -made of basalt lava flows, no ash or pyroclastics -basaltic magma, low gas trapping 14

Composite Cone/Stratovolcano 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 15

Cinder Cones Smallest volcanic features have large craters with steep slopes of 30-40 Paricutin, Mexico Generally forms on continents Explosive eruptions Built 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 Paricutin, Mexico, cinder cone soon after its birth in 1943 in a Mexican cornfield. 16

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