| (ch. 5, cont.) Volcanic Landforms 1. Calderas -large collapse depression where the volcano vent was a. Crater Lake type (Oregon) (fig 5.22 p 159) -after the eruption, the mountain fractures and caves in -a little greater than 1 km b. Hawaiian type -mafic -hot spot forms massive volcano (shield volcano) and it sinks b/c its so heavy -and as magma chamber empties, it caves in c. Yellowstone type (fig 5.24 p 160) -area is highly felsic, silicic; felsic & intermediate -collapse of a volcano, followed by an eruption 2. Fissure -fracture in Earth's crust through which magma migrates -mafic (basaltic) magmas 3. Lava Dome (fig 5.26 p 162) (Mt. St. Helen's) -pressure makes magma eject, then after pressure is released, the remaining magma sits in it like a bowl; the top crystallizes and forms a lava dome -eventually, it can plug up a volcano; but if more magma is pushed up or gas is introduced, it can explode again 4. Volcanic Pipes/Necks (fig 5.27 p 163) -conduit that magma flows through to get to the surface -when it crystallizes in there completely and the volcano erodes, the neck may still be there b/c it's tougher Intrusive Igneous Activity Plutons -subterranean (underground) igneous structures (Pluto = god of the underworld) Classification of Plutons Shape: 1) tabular; 2) massive Orientation 1) Discordant (cuts across rock layers) 2) Concordant (parallel to rock layers) Types of Plutons (fig 5.28) 1. Dikes- tabular discordant plutons 2. Sills- tabular concordant plutons 3. Laccoliths- like sills, but the magma is more viscous -intermediate; won't move as easily -forms more of a bubble (blob) than a tabular shape 4. Batholiths- massive pluton -surface exposed is greater than 40 square miles 5. Stock- small batholith -surface exposed is less than 40 square miles Xenolith -fragments of host/country rock; found in igneous masses that are unmelted Columnar Jointing -5-7 sided column; due to slow crystallization of the magma. (fig 5.31) Plate Tectonics & Igneous Activity Convergent Plate Boundaries * Volcanic Island Arc ocean --> <-- ocean * Continental Volcanic Arc ocean --> <-- continent Divergent -not nearly as violent <-- --> Hot Spot -mantle rock is upwelling; forms magma in lithosphere that comes up -plates move; hot spots don't /!\ ! Lab Box 1: Igneous Rocks (Study Chart on p 120) 1. Diorite "white granite" 2. Pink Granite 3. Gabbro 4. Periodite 5. Rhyolite 6. Basalt 7. Porphyritic Basalt 8. Obsidian 9. Pumice 10. Scoria 11. Syenite (white granite w/out quartz) 12. Llanite (porphyritic rhyolite) |