Rock Structures Mt. St. Helens, October 2004
Igneous Structures:Plutons, Volcanoes, & Lava Flows (Oh, My!)
Name this Igneous Feature…
Igneous Dike
Plutonic StructuresXenoliths
Source: William E. Ferguson
Why do we find Plutons at the Surface?
Sierra Nevada Mountains Batholith, California
Uplift & Erosion
Felsic Eruptions:
Explosive Ash and Thick Lava Flows
Ash-Flow Caldera:Crater Lake, Oregon
Pyroclastic Flow
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Stratafication
Bedding (1-300 cm)
Laminations (<1 cm)Massive Strata (>300 cm)
Inter-Bed Structures(within strata)
•Graded Beds•Cross Beds•Dropstones
Outcrop of turbidites, Carboniferous,
northwestern China.
Graded BedsDeath Valley, CA
Intra-Bed Structures(on the
surface of strata)
•Ripple Marks•Mudcracks•Raindrop Impressions
Mudcracks
Glacier National Park, MT
Trace Fossils
Worm Burrows: Middle Silurian, Grimsby Formation, Hamilton, Ontario
CoprolitesMiocene Mammal (WA)