Geosciences 470R/570R
Volcanology: Physical Processes and Petrologic Applications
Study Sheet for Final Examination on 13 May 2015
Emphasis on lectures, on major concepts; supported by required reading (papers); textbook
provides context. Final will emphasize material since midterm. You should know the following:
Types of volcanic landforms, e.g.
Lava dome, Stratocone/stratovolcano/composite volcano, Caldera, Crater, Cinder cone,
Shield volcano, Maar, Diatreme, Tuff ring, Tuff cone, Pillow lava, Littoral cone
Time, length, volume scales
Key terms necessary to understand magmas and to map volcanic rocks
Phenocryst abundance, identity of and relative proportions of various phenocrysts and
microphenocrysts, nature of groundmass (glassy, microcrystalline, vesicularity)
Magma, melt; phyric, aphyric; obsidian, vitrophyre
Flow foliation; basal, carapace, and foreset breccias
Unwelded, partially welded, and welded; fiamme, compaction foliation, cooling unit
Welded ignimbrites versus welded fall deposits; rheomorphism
Lahar, mudflow, giant pumice horizon, jöhkulhlaup, hyaloclastite, pillow
Lava dome versus resurgent dome
Central vent eruption vs. ring-fracture eruption
Maar, diatreme, tuff ring, tuff cone
Basic physical properties of magmas
Relative temperature ranges of terrestrial and extraterrestrial volcanic eruptions, e.g.,
komatiite > basalt > andesite > dacite > rhyolite > carbonatites > sulfur >
cryovolcanic
Principal controls on viscosity
Differences in composition: Metaluminous, peraluminous, peralkaline
Volatiles
Geologic fluids present in or an essential ingredient necessary to form various types of
volcanic products (e.g., surface water in lahars; glacial ice in jöhkulhlaups; silicate
liquids in pahoehoe)
Relative abundances in various compositions of rocks, especially water and sulfur
Controls on solubility for major volatiles
Plinian eruptive plumes and underlying vent (be able to sketch)
Components (regions/phases); controls
Primary versus secondary plumes
Pyroclastic eruptive products, characteristics, transport mechanisms, and depositional controls
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Fall deposits (both unwelded and, uncommonly, welded)
Flow deposits (both block-and-ash flow and ignimbite/ash-flow tuff)
Surge deposits
Transport processes: Which are transported by: Mass-flow and resulting from
gravitational collapse or explosive collapse of a lava dome? Suspension and favored
by low particle concentration and subvertical particle trajectory? Mass-flow and
resulting from eruptive column collapse or eruptive fountaining of pumice? Traction
and favored by low particle concentration and subhorizontal particle trajectory?
Suspension and favored by low magma viscosities and proximity to eruptive vent?
Silicic lavas (be able to sketch the zoning diagrams)
Eruptive sequence and processes; flow-dome complex; lava domes versus lava flows
Primary features—zoning and controls
Features developed during cooling—zoning and controls
Zoning in ash-flow tuffs/ignimbrites (be able to sketch the zoning diagrams)
Features developed during emplacement (standard ignimbrite flow unit)—layers, controls
Features developed during post-emplacement welding and compaction—zoning, controls
Features developed during cooling—zoning, controls
Zoning in pyroclastic surge deposits (be able to sketch)
Depositional facies (sandwave, massive, planar)
Caldera cycle
Three-fold stages [A. Precollapse volcanism; B. Ash-flow eruption and concurrent
collapse; C. Resurgence and post-caldera deposition] and components of each
Concept of repose times
Ties to key examples (e.g., Long Valley, Valles; Creede; Yellowstone, Pantelleria) will
help your understanding
Eruptive styles: Eruptive behavior/characteristics and typical volcanic products
Plinian
Vulcanian
Peléan
Strombolian
Hawaiian
Surtseyan
Intermediate, mafic, and ultramafic (including carbonatitic) lava flows
Characteristics, including relative viscosities
Controls
Tube versus channel delivery of lava to the lava flow front
Stratovolcanoes
Characteristic behaviors (e.g. Hildreth and Lanphere, 1994)
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Debris-avalanche deposits
Hummocky topography
Amphitheater/sector collapse
Hydromagmatism
Impact of water/mass ratio
Controls by depth of aquifer, depth of water
Volcanic hazards
Lessons from Mount St. Helens, USA
Lessons from Pinatubo, Philippines
Lessons from Unzen, Japan
Lessons from Nevado del Ruiz/Armero, Colombia (e.g., Voight, 1990)
Threats at other sites
Mineral deposits
Major types of deposits relevant to volcanology
Surficial landforms of porphyry deposits
Extraterrestrial volcanism
Key characteristics distinguishing Moon, Mercury, Venus, Mars, Jupiter, Io, Neptune
Processes: Hot spots, plate tectonics, gravitational deformation, bombardment, surface
heating
Implications for presence or absence of plate tectonics; dead vs. dynamic planet
Controls on sizes and types of volcanoes, including surface temperature, atmospheric
pressure
Cryovolcanism
Volcanism and climate
Weather vs. climate
Layering of atmosphere: Troposphere, stratosphere, mesosphere
Importance of injection of material into stratosphere
Importance of magmatic composition (S content and explosivity) and hydromagmatism
Importance of tropical vs. temperate vs. polar latitudes
Spatial and time scales of climatic influences of volcanic eruptions
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