![Page 1: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/1.jpg)
Volcanic eruptions Factors that determine the violence of
an eruption • Composition of the magma • Temperature of the magma• Dissolved gases in the magma
Viscosity of magma • Viscosity is a measure of a material's
resistance to flow
![Page 2: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/2.jpg)
Volcanic eruptions Viscosity of magma
• Factors affecting viscosity • Temperature (hotter magmas are less viscous) • Composition (silica content)
• High silica – high viscosity • Low silica – more fluid
• Dissolved gases (volatiles) • mostly H2O and CO2
• Gases expand near the surface
![Page 3: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/3.jpg)
Volcanic eruptions Viscosity of magma
• Factors affecting viscosity• Dissolved gases (volatiles)
• Provide the force to extrude lava• Violence of an eruption is related to how
easily gases escape from magma • Easy escape from fluid magma • Viscous magma produces a more violent
eruption
![Page 4: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/4.jpg)
A low silica lava flow
![Page 5: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/5.jpg)
A high silica flow
![Page 6: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/6.jpg)
Pyroclastics
• Pyroclastic material: fragments of rock formed during eruptions– Ash and dust: fine, glassy fragments– Lapilli: walnut sized rocks– Bombs: magma ejected into the air cools and
forms rounded rocks– Blocks: ejected as large rocks
![Page 7: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/7.jpg)
Volcanoes General features
• Conduit, or pipe carries gas-rich magma to the surface
• Vent, the surface opening (connected to the magma chamber via a conduit)
• Crater• Steep-walled depression at the summit • Caldera (a summit depression greater than 1
km diameter)
![Page 8: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/8.jpg)
Volcanoes Types of volcanoes
• Shield volcano• Broad, slightly domed (like a shield)• Primarily made of fluid lava • Generally large size
![Page 9: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/9.jpg)
A shield volcano
![Page 10: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/10.jpg)
Volcanoes Types of volcanoes
• Cinder cone • Built from ejected lava fragments • Steep slope angle • Relatively small size
![Page 11: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/11.jpg)
Sunset Crater – a cinder cone near Flagstaff, Arizona
![Page 12: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/12.jpg)
Volcanoes
Types of volcanoes • Composite cone (or stratovolcano)
• Most are adjacent to the Pacific Ocean (e.g., Mt. Rainier)
• Large size • Interbedded lavas and pyroclastics • Most violent type of activity
![Page 13: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/13.jpg)
A composite volcano (stratovolcano)
![Page 14: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/14.jpg)
Mt. St. Helens – a typical composite volcano
![Page 15: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/15.jpg)
Mt. St. Helens after eruption
![Page 16: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/16.jpg)
A size comparison volcanoes
![Page 17: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/17.jpg)
Other volcanic landforms
Calderas • Steep walled depression at the summit • Formed by collapse • Nearly circular • Size exceeds one kilometer in diameter
![Page 18: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/18.jpg)
Crater Lake in Oregon
![Page 19: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/19.jpg)
Hot Spots
![Page 20: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/20.jpg)
Locations of some of Earth’s major volcanoes
r
![Page 21: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/21.jpg)
Continental and island volcanic arcs
![Page 22: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/22.jpg)
Super volcanoes
• “super eruptions:” – eject magma with a mass greater than 1015
kg, equivalent to a volume greater than 450 km3
• explosive eruptions of this magnitude have a volcanic explosive index (VEI) of 8 or above and produce > 1000 km3 of fragmental deposits
• A “super volcano” can be defined as a volcano that has produced at least one explosive super eruption.
![Page 23: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/23.jpg)
![Page 24: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/24.jpg)
![Page 25: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/25.jpg)
Super eruptions require:
- ENORMOUS volume of highly viscous magma (silica content >60%) accumulating in shallow magma chambers, which are part of even bigger magma reservoirs
- High volatile content (mostly water vapor)
* Thick, relatively low-density crust, common in continents or old island arcs help to create such HUGE magma reservoirs.
![Page 26: Volcanic eruptions Factors that determine the violence of an eruption Composition of the magma Temperature of the magma Dissolved gases in the magma](https://reader036.vdocuments.us/reader036/viewer/2022070401/56649f165503460f94c2cfa0/html5/thumbnails/26.jpg)
Explosive eruptions can happen if (when?):
• The magma body becomes partially solid and the volatiles are forced into the remaining liquid, making the liquid saturated in gas
• Fresh batch of hot magma intrudes in the magma chamber
• The gas-rich liquid magma escapes from the semi-solid crystal mush and is stored beneath the roof of the magma chamber, and,
• Earthquakes and faulting fracture a magma chamber and/or “shakes up” the magma chamber