Igneous Structures: Intrusive
Viscosity
• Units: pascal-seconds (kg/m-sec)
• How many pascals pressure x how many
seconds to squash fluid flat?
• Viscous: Material flows as long as pressure is
applied, however small
• Pseudoviscous: Material flows after some
threshold stress
Viscosity of Common Materials
Material
Viscosity Pa-Sec
Hydrogen gas, 15 degrees K
0.0000006 (6 x 10-7)
Air, 0 degrees C
0.000017 (1.7 x 10-5)
Liquid Hydrogen
0.00001 (10-5)
Water 0 degrees C
0.0018 (1.8 x 10-3)
Water 100 degrees C
0.0003 (3 x 10-4)
Heavy Machine Oil 15 C
0.66
Glycerin, 20 degrees C
1.5
Honey 20 degrees C
1.6
Geologic Viscosities
Material
Viscosity Pa-Sec
Basalt Lava
1000
Rhyolite Lava
1,000,000
Rock Salt
1014 (Pseudoviscous)
Marble
1016
Granite, Quartzite
1018 - 1020
Asthenosphere
1019 - 1020
Deep Mantle
1021 - 1022
Shallow Mantle
1023 - 1024
What Drives Magma?
• Magma is typically 10% lighter than equivalent
solid rock
– Why pressure inhibits melting
• Buoyancy drives magma upward
– Weight of rock around volcanic conduit > weight
of magma
• Gas pressure powers volcanic eruptions
• Mafic (dense) rocks can sink in crust by
viscous flow
Plate Tectonics and Volcanoes
Cullain Layered Complex, Scotland
Cullain Layered Complex, Scotland
Cullain Layered Complex, Scotland
Cullain Layered Complex, Scotland
Cullain Layered Complex, Scotland
Filter Pressing, Scotland
Filter Pressing? Scotland
Lava Flows and Dike, Scotland
Magma Mixing, Scotland
Pseudotachylite, Scotland
Sill, Scotland
Extrusion Striae, Scotland
Keeweenawan Sills, Ontario
Keeweenawan Sills, Ontario
Columnar Jointing, Ontario
Batholith, California
Sierra Nevada Batholith
Roof Pendants, Sierra Nevada
Columnar Jointing, Devil’s Postpile, California
Columnar Jointing, Devil’s Postpile, California
Columnar Jointing, Idaho
Columnar Jointing, Scotland
Devil’s Tower, Wyoming
Phonolite, Devils Tower, Wyoming
Jointing, Devils Tower, Wyoming
Laccolith, Bear Mountain SD
Laccolith, Wyoming
How Laccoliths Form
How Devil’s Tower Formed
Intrusions, Mount Rushmore
A Rarely Seen Perspective
Granite Intrusion, Black Hills
Dike and Shear Zone, Washington
Dikes, Lead, South Dakota
Dike, Redgranite, Wisconsin
Dike, Redgranite, Wisconsin
Dike, Black Hills, SD
Palisades, New Jersey
The Palisades
Base of Palisades Sill, NJ
Intrusion Breccia