GEOL 108Lg 1st Edition Lecture 7Outline of Last LectureI. Earthquake HazardsII. Ground Shaking EstimatesIII. Omori’s Law OverviewIV. Gutenberg Richter RelationshipV. Review of Magnitude, moment, intensity, shear modulusOutline of Current LectureI. Physics and Geology of VolcanoesII. Effusive vs. Explosive VolcanoesCurrent LectureVolcanoes I*This and the following lecture go over mainly the physics and chemistry of how volcanoes work – generally, either they are explosive or they’re not.The distribution of Volcanoes is given by the plate boundaries the‐ largest amount of volcanism happens at the spreading centers (most of them are underwater, so we don’t really feel the impacts of these volcanoes).‘Ring of Fire’ around the pacific that’s associated with plate subduction ‐ this is where most of the explosive volcanoes are found. We already discussed that hot spot volcanism is due to hot mantle plumes rising beneath the earth.Volcanism is associated with plate tectonics – distribution of active volcanoes can be seen below, as indicated by the red dots in the map.Volcanism is associated with plate tectonics – distribution of active volcanoes can be seen below,as indicated by the red dots in the map.Melting of mantle material is caused by:o a decrease in pressureo an increase in the temperature (hot spot)Subduction, water released from sediments going down to the mantle water‐ induced melting(asthenosphere).The eruption of a volcano emits mainly Hydrogen, Nitrogen, C02 and Water – a main theory about our earth’s beginnings is that volcanic eruptions formed the oceans.Volcanoes pose a great hazard, but are also absolutely crucial to earth evolution. Andean, Silicic or Subduction Zone Volcanoes are all type of explosivevolcanoes.Principal types of volcanoes are: Stratovolcanoes (also known as Composite Volcanoes), Shield, Fissure, and Cinder cone. Images of each can be seen below. Refer to lab exercise from this week to investigate further information regarding these types of volcanoes.Volcanic HazardsPyroclastic flows: hot ash cloud big‐ hazardA pyroclastic flow is a current of volcanic ash, gas and rock (collectively known astephra)Magma chamber: effects impurities in the water depends ‐ on the amount of water content higher the‐ water content, lower the water temperature will melt‐ more easily, weakensbonds between atoms.Basaltic Volcanic Eruptionsthe lava flow, in some cases like riversPa Hoe Hoe, A’a (different types of lava; their Hawaiian names)Pa Hoe Hoe: Lava with a smooth and glassy surfaceA’a: Surfaces are fragmented and rough, “rocky” in appearanceShield Volcano: Mauna Loa Smoo‐ th Flow – almost flat appearance at its surfaceCentral vent that leads to lava flow; site flank eruption where lava flows out and layer on layer of lava solidifies and forms “gentle” shape.V Shape Stratovolcan‐ o: Mount Fuji Pyroclastic‐ layered eruptionDykes (crack like features of eruption); central vent is plugged, pyroclastic layers (mixture of rock and erupted gas). *Review of how volcanoes erupt, as mentioned earlier in the lecture*Igneous RocksSubduction ZoneWater rises from sediments melt‐ ing mantle wedge intermingling in different setngs‐(ocean/ocean setng) – intermediate.Continental crust has more silicate ‐ melt the mantle wedge and some parts of continental lithosphere, maybe even the crust (Continental plate