Unformatted text preview:

Volcanoes- Volcano Typeso Stratovolcanoes Large, cone-shaped volcano Composed of alternating layers of lava and tephrao Shield Volcanoes Broad, slightly domed-shaped (like an inverted shield) Made by lateral flow of low-viscosity basaltic lava Have a low slope and cover large geographic areas Mauna Loa on Hawaiio Cinder Cone – conical piles of tephra- Eruptions to Remembero Mt. St. Helens – May 18, 1980 – 8:32 p.m. The blast devastated 600 km squared and killed 61 people Lahars plugged the Toutle River – closed the Columbia Ash fell in North Dakota – highways and rail lines stopped Destroyed timber valued at several 100 million dollars One side erupted, rather than erupting straight up- Volcanic Hazardso Earthquakeso Tsunamis – water explosions create giant waves- Mitigating Hazardso Danger assessment maps Delineate danger areas- Pyroclastic flows, lahars- Eruptive Styleo Effusive eruptions – produce lava flows Can produce huge lava fountains Commonly basaltic, lead to formation of shield volcanoes Pele’s hair and tears, bombso Basaltic Lava Flows Pahoehoe vs A’a- Pahoehoe – a Hawaiian word describing basalt with a glassy, ropy textureo Forms when extremely hot basalt forms a skin- A’a – is a Hawaiian word describing basalt that solidifies with a jagged, sharp,angular textureo Forms when hot flowing basalt cools and thickens Underwater, basalt cools instantly; it cannot flow It cools to form a rounded blob called a pillow Common on the mid-ocean ridge- Continental Hot-Spot Volcanoeso Continental hot-spot – cutes a continental plate Yellowstone – erupted and created a caldera- Flood Basalt Eruptionso Voluminous lava eruptions above a plumeSedimentary Rocks- Sedimentary Rockso Sediments are the building blocks of sedimentary rockso Sediments are diverse, as are the rocks made from themo 4 classes: Clastic – made from weathered rock fragments (clasts) Biochemical – cemented shells of organisms Organic – the carbon-rich remains of plants Chemical – minerals that crystallize directly from watero Clastic Sedimentary Rocks Clastic sedimentary rocks reflect several processes- Weather – generation of detritus via rock disintegration- Erosion – removal of sediment grains from rock- Transportation – dispersal by wind, water, and ice- Deposition – settling out of the transporting fluid- Lithification – transformation of loose sediment into solid rocko Burial, compaction, cementation Classified on the basis of texture and composition- Clast (grain) size – the average diameter of clastso Range from very coarse to very fineo Boulder, cobble, pebble, sand, silt, clayo With increasing transport, average grain size decreases- Clast composition – the mineral makeup of sedimentso May be individual minerals or rock fragmentso Mineral identities provide clues about… The source of the sediment The environment of deposition- Angularity and sphericity – indicate degree of transporto Grain roundness and sphericity increases with transport Well-rounded – long transport distances Angular – negligible transport- Sorting – the uniformity of grain sizeo Well-sorted – uniform grain sizeso Poorly sorted – wide variety of grain sizeso Sorting becomes better with distance from the source- Character of cemento Cement – minerals that fill sediment poreso Common cements; Silica Calcite Hematite Clay minerals- Coarse clastics – composed of gravel-sized clastso Breccia – composed of angular fragments Angularity indicates a lack of transport processing Deposited relatively close to sourceo Conglomerate – comprised of rounded gravel Indicates water transport- Clasts bang together forcefully in flowing water- Collisions round angular corners and edges of clasts Conglomerates are deposited at a distance from the sourceo Sandstone – clastic rock made of sand-sized particles Forms in many depositional settings Quartz is, by far, the dominant mineral in sandstones Sandstone varieties- Arkose – contains abundant feldspar- Quartz sandstone – almost pure quartz- Fine clastics – composed of silt and clayo Silt-sized sediments are lithified to form siltstoneo Clay-sized particles form shaleo Chemical Sedimentary Rocks Comprised of minerals precipitated from water solution Evaporates – created from evaporated seawater- Evaporation triggers deposition of chemical precipitates- Examples include halite (rock salt) and gypsum (dry wall) Travertine – calcium carbonate (CaCO3) precipitated from groundwater where it reaches the surface- Dissolved calcium reacts with bicarbonate- CO2 expelled into the air causes CaCO3 to precipitate Dolostone – limestone altered by Mg-rich fluids- Looks like limestone, except…o It has a sugary texture and a pervasive porosityo It weathers to a buff, tan color Replacement chert – nonbiogenic in origin- Many varietieso Flint – black or gray from organic mattero Jasper – red or yellow from Fe-oxideso Petrified wood – wood grain preserved by silicao Agate – concentrically layered ringso Biochemical and Organic Rocks These are sediments derived from living organisms- Biochemical – hard mineral skeletonso Biochemical limestone – CaCO3 skeletal (shell) remains Warm, tropical, shallow, clear, O2-rich, marine water Diverse organisms (plankton, corals, clams, snails, etc.) Many textural varietieso Chert – rock made of cryptocrystalline quartz Formed from opalline silica (SiO2) skeletons- Diatoms- Radiolarians Opalline silica added to bottom sediments dissolves Silica pore fluids solidify to form chert nodules or beds- Organic – cells of plants, algae, bacteria, and planktono Made from organic carbon Coal – altered remains of fossil vegetation Oil shale – shale with heat altered organic mattero Flint continued… Crytocrystalline: hardly classifies as a crystal structure Composition similar to the mineral quartzo Sedimentary Structures Features imparted to sediments at or near deposition- Layering- Surface features on layers- Arrangement of grains Help decipher conditions at or near time of deposition Sedimentary rocks are usually layered – “stratified”- Arranged in planar, close-to-horizontal beds- Bedding is often laterally continuous for long distances- Beds are often similar in composition, color, and texture- Bedding


View Full Document

OSU EARTHSC 1100 - Volcanoes

Download Volcanoes
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Volcanoes and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Volcanoes 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?