Exam 2 Geol 101

Chapter Five - Volcanoes

  • How magma types (felsic, intermediate, mafic) relate to silica content, viscosity, gas content,
    explosiveness, and types of volcanoes

    • felsic: 70%> silica content, high viscosity, high gas content bc it gets stuck in the viscous lava, less eruptions, though gas build up creates extremely dangerous eruptions

    • intermediate: middle ground between mafic and felsic lavas

    • mafic: 40%> silica content, low viscosity and gas content, erupts more due to lack of viscosity and gas build up

  • Sizes of pyroclastic material (tephra)

    • ash: <2mm in size

    • lapilli: 2-64mm in size, marble to golf balll

    • blocks/bombs: 64mm in size, golf ball size, close to vent bc they don’t fly far

    • spindle bombs: flys through air, creating a football with a tail

  • Types of volcanoes: their shapes, sizes, eruptive styles, and what rock types they produce. Be able to identify
    based on pictures, diagrams or descriptions.

    • calderas: naughty, 1 mile depressions. explosive eruptions of thick rhyolitic lava, continental hot spots

    • stratovolcanoes: naughty, movie volcano, cone-shaped mountains, composed of alternating ash and lava layers, andesite = andes mountains

    • cinder cones: made of cinders, monogenetic, explosive/basaltic cinder, lava spills out, no structural integrity

    • lava domes: naughty, unstable mound of viscous rhyolitic lava, 100’s feet tall, independent mounds

    • shield volcanoes: gentle slopes, Idaho volcanos, lava flows, non-explosive

    • fissure: large volume eruptions, basaltic lava, oozes out of cracks

  • Know an example of each volcano type (for example, Mt St Helens is a stratovolcano)

    • calderas: Crater Lake

    • stratovolcanoes: andes mountains

    • cinder cones: cinder cone butte

    • lava domes: mount pelee

    • shield volcanoes: rocky butte

    • fissure: Kings Bowl

  • Volcanic hazards and how they are associated with each volcano type

    • calderas: pyroclastic flows, tephra, lava flows, high viscosity

    • stratovolcanoes: lava flows, pyroclastic flows, lahars, gases, ashfall

    • cinder cones: tephra, ashfall, lava flows

    • lava domes: gases, highly viscous, pyroclastic flows if they collapse

    • shield volcanoes: lava flows, non explosive

    • fissure: Lava flows, gases,

  • Types of basaltic lava flows; a’a and pahoehoe

    • a’a: rough jagged surface

    • pahoehoe: smooth, ropy surface

Chapter Six - Weathering

  • Physical (mechanical) weathering processes:

    • frost wedging: water works its way into cracks, freezing, causing it to expand. freezing numerous times can cause rock to break apart

      • climate-dependent process

      • Stanley Idaho: alternates between freezing and thawing enough to make a difference.

    • unloading (pressure release): overlying rock is scraped away, allowing pressure to decrease and the rock beneath expands.

    • root wedging: root systems work their way through the rocks fractures

  • Chemical weathering processes:

    • oxidation: reaction btw iron-rich minerals and oxygen: like rust

      • sandstone is quartz glued together using oxidized hematite

    • dissolution: where minerals are dissolved by carbonic acid; forms caves in limestone and marble

  • Factors that affect weathering rates

    • surface area of rock, rock characteristics, and climate

Chapter Seven – Sedimentary Rocks

  • How sediment turns to rock

    • lithification: deposition (dropped), compaction (accumulation, forcing clasts to form together), cementation (groundwater moves btw the grains and leaves behind mineral deposits, bonding grains to each other

      • drop, compact, glue together

  • Deposition

    • where clasts are dropped or settled out

  • Depositional environment examples

    • alluvial fans, rivers, lakes, glaciers, beaches, marine,

  • Clastic sedimentary rocks:

    • conglomerate: large rounded clasts, poor sorting

    • breccia: angular clasts, similar to congolmerate

    • sandstone: sand sized particles, typically feldspar, quartz, or rock fragments, well sorted

    • shale: mostly clay and fine silt, fine grain, splits into layers, clay minerals

    • mudstone: very fine, clay and silt sized particles, like shale but does not split into layers

  • Biochemical sedimentary rocks:

    • limestone (micrite, chalk, coquina)

      • micrite: fine grained, smooth, lacks visible fossils, clay or organic matter

      • chalk: microscopic marine organisms, soft, white limestone

      • coquina: entirely made of shell fragments cemented together

    • coal (peat, bituminous coal)

      • peat: initial stage of coal; loosely compacted organic material

      • bituminous: high carbon content, highly compacted peat

    • chert: composed of silica, skeletons marine organisms,

  • Sediment sizes and how they relate to energy of depositional environment

    • gravel: bigger than bb size

    • sand: 1/16 to 2mm

    • mud: silt/clay, 1/256mm

  • Rounding and sorting and what they tell us about rock’s history

    • rounding are products of abrasion. Being tossed around in a river breaks off the angular edges

    • sediment sorting is a product of cementation. river beds will have poor sorting where as good sorting may come from sand dunes

  • Sedimentary rock names and likely depositional environments

    • conglomerate: high energy environment such as angular fan or river

    • breccia: landslides, fault zones

    • sandstone: deserts, beaches, shallow marine environments

    • shale: deep marine basins, floodplains, lagoons

    • mudstone: deep oceans, lakes

    • micrite: low-energy lagoons, tidal flats

    • chalk/coquina: coral reefs, shallow marine environemnts

    • coal: swamps, waterlogged environments

    • chert: deep ocean basins

Chapter Eight – Metamorphic Rocks

  • Metamorphism is a solid state change (no melting!)

    • can be slow or extreme solid state

    • meta = change

    • morph = form

  • Parent Rock

    • called protolith

    • the original rock before metamorphism

    • limestone to marble

  • Sources of heat for metamorphism

    • magma, deep burial, friction

  • Temperature range for metamorphism

    • 200 to 800 degrees Celsius

    • 400 -1500 F

  • Two types of pressure

    • confining pressure: pressure in all directions

      • could happen if buried

    • differential pressure: pressure in one direction

      • produces foliation: the arrangement of minerals

        • could happen at convergent plate boundaries

  • Foliated metamorphic rocks:

    • slate: breaks into planes, no visible micas, fine grain; protolith: shale

    • phyllite: breaks alone wrinkled surfaces, sheen, fine grained, protolith: mudstone

    • schist: visible micas, protolith: granite or shale

    • gneiss: dark/light colroed layers, few to no micas, coarse grained, protolith: shale/granite

  • Nonfoliated metamorphic rocks:

    • marble: tightly packed CaCO3 crystals

    • quartzite: contains quartz, well cemented, protolith: sandstone

    • anthracite coal: black, shiny. Resembles obsidian, though is brittle, conchoidal fractures

  • Types of metamorphism:

    • contact: High T, low, P, rocks are heated by the intrusion of magma into cooler surrounding rocks, creates aureole (zone of alternation)

    • regional: Low. to med T, high P, associated with mountain building and convergent boundaries

    • burial: Low T and P, when rocks are deeply buried under thick layers of sed, leads to slate and phyllite from shale

    • impact: High T and P, due to impact of a meteorite or asteroid.