Rock Structures Mt. St. Helens, October 2004

Igneous Structures:Plutons, Volcanoes, & Lava Flows (Oh, My!)

Plutons

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

Volcanic Structures

Maficvs.

Intermediate/Felsic

Mafic Eruptions:Passive

Lava Flows

Lava Flows

Aa Lava Flows

Pahoehoe Lava Flows

“Window” into Lava Tube

Lava Tubes

Pillow Structure

Pillow Structures

Columnar Structures

Shield Volcano

Summit Caldera

Cinder Cones

Flood Basalt Flows

Felsic Eruptions:

Explosive Ash and Thick Lava Flows

Stratovolcano

Lava Dome

Ash Flow Caldera

Ash-Flow Caldera:Crater Lake, Oregon

Pyroclastic Flow

Pyroclastic Flow

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Sedimentary Structures

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

Cross BedsZion National

Park, UT

Dropstones

Norway

Intra-Bed Structures(on the

surface of strata)

•Ripple Marks•Mudcracks•Raindrop Impressions

Ripple

Marks

Mudcracks

Glacier National Park, MT

Raindrop Impressi

ons

Fossils

Trace Fossils

Worm Burrows: Middle Silurian, Grimsby Formation, Hamilton, Ontario

CoprolitesMiocene Mammal (WA)