What is the Viscosity of a Volcano?
Viscosity is a fluid's resistance to flow, which is important in volcanic processes. Many factors affect a magma's viscosity:
- Temperature Ex) Examination of a rhyolitic melt, temperature decreases from 1300 degrees Celsius to 600 degrees Celsius the viscosity increases by more than eight orders of magnitude.
- Silica and water content Ex) More silica in the magma, the more viscous the magma will be due to the strong silica-oxygen bonds. When water is added, the viscosity decreases because of water breaking the silica-oxygen bonds.
Flow of Volcanoes.
Two types of flow:
Determining the type of flow requires the use of rheology. Rheology is the study of the flow of any matter. The Reynolds (Re) number can calculate the flow of a fluid to either be turbulent or laminar. If the Reynolds number is less than 10 Re, it is laminar. If it is over 100 Re, it is turbulent. The areas in between mean that the liquid flow can flow either way. Lava flow is dependent on the factors: viscosity, rheologic properties, composition and temperature.
- Turbulent-Happens when the flow patterns are all disorganized and there is an exchange of fluid between these areas.
- Laminar-Happens when the motion of the particles of fluid are in an organized fashion and are moving in straight lines, parallel to the walls.
Determining the type of flow requires the use of rheology. Rheology is the study of the flow of any matter. The Reynolds (Re) number can calculate the flow of a fluid to either be turbulent or laminar. If the Reynolds number is less than 10 Re, it is laminar. If it is over 100 Re, it is turbulent. The areas in between mean that the liquid flow can flow either way. Lava flow is dependent on the factors: viscosity, rheologic properties, composition and temperature.
Causes of Volcano Eruptions
An explosive eruption includes three different processes: fragmentation of the magma, fragmented mass blasting through the vent to the surface and the climb of the eruption column. When the pressure within the magma outweighs the strength of the rock, the explosive eruption occurs. Thermal energy within the magma causes these eruptions. Thermal energy is transferred into kinetic energy of the eruption column through gases expanding into air bubbles. The viscosity of magma, dissolved eruption volatiles and mass eruption rate are all variables that will affect the eruption.
3 Major Types of Volcanic Eruptions
Vulcanian
These eruptions are considered small to moderate eruptions. They can shoot material to heights up to 20km and are characterized as violent eruptions. These eruptions occur due to ballistic ejection of blocks and bombs, atmospheric shock waves and the emission of tephra and juvenile components. Pressure is greatly increased to be able to accelerate the ejection of material to a far distance. Calculated velocities are 200 m/s, but observations at volcanoes have been up to 400 m/s.