GEOL 1425 1ST Edition Lecture 15 Outline of Last Lecture I. Principles in stratigraphyII. Reconstructing geologic historyIII. Geologic timeIV. Measuring absolute timeOutline of Current Lecture I. Volcanoes as geosystemsII. Lava and other volcanic depositsCurrent Lecture—Volcanoes 1I. Volcanoes as geosystemsA. Deep temperatures within asthenosphere reach 1300 degrees C, which causes the rocks to begin to melt. Magma eventually travels up to the earth’s surface as it accumulates. Molten rock tends to want to find ways to float to the surface (they’re less dense than the rocks that make them). B. Parts of this geosystem: rocks, magmas and lavas, landforms associated with processes of melting and eruptionC. Magma originates in the asthenosphere and rises through the lithosphere to form a crust, eventually reaching the surface. II. Lavas and other volcanic depositsA. Differences depend on chemical composition of lava, its gas content (the more gas in the lava, the more violent its eruptions are), and its temperatures (lower silica content and lower temperature= more viscous).B. Types of lava:These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.a. Basaltic lava—extrusive mafic composition, most common type of melt. Mantle plume that rises through the crust—volcanic hot spot (where lava comes out) stays the same, but the plates move around. Often in reds in yellows; can move downhill pretty quickly (100km/hr) b. Pillow lava—cools underwater. Pillow-like structures in fine grained basaltic lavac. Andesitic lavas—extrusive rock, mainly above subduction zones along active continental or oceanic margins, temperatures lower then basaltsd. Rhyolitic lavas—extrusic rock with felsic composition (high in sodium and potassium). Flows very slow and tends to pile up in thick bulbous deposits, rich in silica so stickiest and least fluidC. Pyroclastic deposits—volcanic ejecta, things thrown out of volcano often from explosive eventsa. Shattering lava causes it to be erupted out of the cone, and different sizes of particles are generated. Classified by sizeb. Pyroclastic flow—one of the deadliest to life. Flows downwards due to flow of gravity and very deadly. Rolls downhill and can move very quickly.D. Eruptive styles and landformsa. Central eruptions: shield volcanoes and volcanic domes, cinder-cone volcanoes, stratovolcanoes (mix of thick and thin matter), volcanic craters (where lava hasn’t quite reached surface), calderas (all that’s left at top ofvolcano is a damn big hole), diatremes (volcanic neck/pipe that remains when the surrounding cone has been eliminated)b. Eruptions from linear cracks: fissure eruptions (large vertical cracks largesteruptions and mostly in min-oceanic ridges), basalt, ash flow