What comes out of a volcano?
- Lava Flows - Molten rock that has flowed out onto the Earth’s surface. Cools on surface = extrusive igneous rock.
- Basaltic Lava Flows - Very hot, low silica, and low viscosity. They can flow rapidly (up to 100 km/hr) & for long distances (up to several 100 km).
- Pahoehoe - thin, 'ropey' texture.
- Aa - rough, jagged, 'clinkery'
- Lava tubes - forms when the surface cools and solidifies and the lava beneath still flows, forming a tube.
- Columnar Jointing - Solidified flows may contract with vertical fractures that are hexagonal in cross-section. Clochán an Aifir or Giant’s Causway in County Antrim, Ireland (http://en.wikipedia.org/wiki/Giant's_Causeway)
- Pillow basalts - forms when basalt erupts underwater, forming a pillow-like structure.
- Intermediate Lava Flows - Higher SiO2 content = more viscous lava. Flow slowly, staying near the vent
- Felsic Lava Flows - High SiO2 content = most viscous. Rarely flows, plugs the vent as a lava dome.
- Basaltic Lava Flows - Very hot, low silica, and low viscosity. They can flow rapidly (up to 100 km/hr) & for long distances (up to several 100 km).
- Pyroclastic Material - fragments that get ejected from the vent during an eruption. Classified by size:
- Ash and dust – fine, glassy. Amount of ash is dependent upon:
- Distance from vent
- Type of eruption
- Size of eruption
- Pumice – from "frothy" lava
- Cinders – "pea-sized"
- Lapilli – "walnut" size
- Particles larger than lapilli – Blocks & Bombs
- Ash and dust – fine, glassy. Amount of ash is dependent upon:
- Pyroclastic flows - Hot gases infused with ash flow at speeds of 200 km per hour & 800º C down the flanks of a volcano. Examples: Mt. Vesuvius Mt. Shasta Mt. St. Helens
- Lahars - How to make a lahar: Add water + volcanic material = lahar. Water sources include melted glaciers, displaced lakes, and rain
- Gases - 1 to 5% of magma by weight Mainly water vapor and CO2
Active vs. Extinct
- Active - Erupting, recently erupted or likely to erupt.
- Dormant - Volcano that has not erupted in 100s to 1000s of years (but could still do so).
- Extinct - No longer capable of erupting. Tectonic changes can shut off the magma “fuel.” After extinction, erosion.
Predicting Eruptions - These signs indicate that an eruption is imminent. Cannot predict the exact timing or the style.
- Earthquake activity: Magma flow increases seismicity.
- Heat flow: Magma causes volcanoes to heat-up.
- Changes in shape: Magma causes expansion.
- Emission increases: Changes in gas mix and volume