Geology 101 - Lecture 8
Volcanic Rocks
Review of last time:
Materials erupted: lava, pyroclastic material, gas
Basaltic magmas usually erupt as lavas; and andesite and rhyolite magmas
tend to form more explosive eruptions (pyroclastic material)
1. Lava (see notes from last time)
2. Pyroclastic material:
Andesite and rhyolite: typically form the truly explosive eruptions
- Ash - lava particle with diameter less than 2mm
- Pumice - lava that is larger size, lots of gas bubbles
- Bombs/blocks - particles have an average diameter greater than 64 mm
Plinian eruptions - vertical eruption column
Click here to
see someone's active research on these columns
Pyroclastic flows (click here for an
example)
3. Gases erupted - 70% water vapor, 15% carbon dioxide, 5%
nitrogen, 5% sulfur dioxide
OTHER HAZARDS:
Lahars (volcanic mudflows). A significant danger associated with
explosive eruptions on volcanoes with lots of snow and glaciers
Potential Volcanic Hazards from Future
Activity of Mount Baker, Washington
FILM: PERILOUS BEAUTY - THE HIDDEN DANGERS OF MT. RAINIER
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