o The layers record a history of ancient environments o The layers occur only

O the layers record a history of ancient environments

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oThe layers record a history of ancient environments.oThe layers occur only in the upper part of the crust.Sedimentary rocks cover underlying basement rock.LaharsA lahar is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water
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Flows down from a volcano typically along a river valley (water rich, can move up to 100km/h)Mount St. Helens (May 18th, 1980)oThe blast ranged 600km2and killed 61 peopleoLahars plugged the Toutle river, closed the ColumbiaoAsh fell in North Dakota, highway and rail lines stoppedNevado del Ruiz in Columbia (November 13th, 1985)oA small eruption produced enormous lahar that killed 25’000 peopleoBuried town of Armero in 5 meters of ash and mudThe major explosive super volcanoes of the past million years?Mount Vesuvius (79 C.E.)oPyroclastic debris destroyed Pompeii killing 20’000Krakatau (August 27th, 1883)oIsland was obliteratedoMagma chamber was breached by the oceanoTsunami waves killed 36’000 peopleTambora (April 10th, 1815)o71’000 direct fatalitiesoThe year long climate depression caused global crop failures resulting in famineGneiss and other major metamorphic rock types: evolution and protolithsMetamorphic rock: solid-state change of a protolithProtolith: pre-existing rocks, can undergo change in texture and mineralogyFoliated: parallel surfaces or layers in metamorphic rocks (pressure)oSlate: fine-grained, low grade metamorphic shaleoPhyllite: fine-grained mica-rich rock, between slate and schistoMetaconglomerate: metamorphosed conglomerateoSchist: fine to coarse rock with larger micasoGneiss: gneissic banding develops in several ways, original layering in the protolith, extensive high-T shearing, minerals segregate into different layers
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Non-foliated: no planar fabric evident, minerals recrystallized without compression or shear (rock not subjected to stress)oHornfels: fine-grained, variety of metamorphic materialoQuartzite: almost pure quartz in compositionoMarble: coarsely crystalline calcite or dolomiteCarbonate rocks: limestones, dolomites, marble: how?, why?Minerals are classified by their dominant anionLimestone (CaCO3)oSedimentary rocks made of calcium carbonateoSediments derived from the shells of living organismsoHard mineral skeletons accumulate after deathDolostoneoLimestone altered by Mg-rich fluidsoDiagenesis, dolomizationMarbleoLimestone is subjected to heat and pressures of metamorphismoMarble is a metamorphic rock
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