Shield VolcanoesShield Volcanoes
• Low angle volcano constructed principally of basalt lavas
• Examples: Mauna Loa and Kilauea, Hawaii • Thin lava flows • Summit calderas • May have lateral rift zones • May have lava lakes in the crater
SkaldbreidurSkaldbreidur Mauna KeaMauna Kea
StratovolcanoesStratovolcanoes
• A volcano constructed of alternating layers of lava and pyroclastic materials
• Steep slope angles (~35°) • Examples: Fuji, Japan and Kliuchevskaya,
Kamchatka • May exhibit persistent activity (Etna, Sicily) • Volumes of erupted lava proportional to
repose time
• Tholeiitic or calc-alkaline compositions • Merge to andesites • Continuous feeding from depth into a
shallow chamber • May be associated with fissures and
monogenetic scoria cones • Cones may be truncated by edifice collapse
– Example: Augustine, Alaska
• Composed of volcanoes that erupt only once
• Common edifice is a scoria cone • Tuff rings and small shields are also
common • Example: Pinacate, Mexico • Vent systems are dikes or pipes (diatremes)
Scoria ConesScoria Cones
Tuff RingsTuff Rings
Pillow LavasPillow Lavas
• Characterized by three parameters
– Height, width, crater width
• Conical shape
DiatremesDiatremes
Tuff ConesTuff Cones
Tuff RingsTuff Rings
• Sandwave beds
• Dry surges
C e rro C o lor ad o, M e x ic oC e rro C o lor ad o, M e x ic o
Basaltic Scoria Cone FieldsBasaltic Scoria Cone Fields
• 10s to 1000s of cones • General elliptical shape • Aspect ratio of 2:1 to 5:1 • 10 to 70 km in length • Areas of extensional tectonics • Elongate perpendicular to σ3
• Widespread in western USA • Pinacate example
San Francisco Volcanic Field
San Francisco Volcanic Field
• Scoria cones aligned along fault planes
Flood Basalt FieldsFlood Basalt Fields
• Extensive sheets of lava flows • Flood the landscape • Associate with crustal dilation • May coincide with mass bioextinctions • Examples: Deccan, India and Columbia
River Plateau, USA
Flow UnitsFlow Units
• Compound lava flows • Overlapping pahoehoe flows • Interconnected lava shields • Lava ponds in depressions • Inward directed dips of large fields • Cut by numerous dike swarms+
Columnar JoinColumnar Join
Central VolcanoesCentral Volcanoes
• A volcano that erupts magmas of various compositions – Mafic to silicic
• Many have a central caldera composed of silicic rocks and rhyolite domes
• A shallow magma chamber is part of the eruptive system
ShastaShasta
Volcano InteriorVolcano Interior
• The eroded core of these volcanoes may expose a granite pluton
• Feeding system may be a ring complex • These may be a host for economic mineral
deposits