What is going to happen next?
What type of volcano is this?
Nature’s pyrotechnics Volcanic Eruptions Nature’s pyrotechnics
Types of eruptions Nonexplosive Explosive
What determines how a volcano erupts? The answer is viscosity! What is viscosity? A fluids ability to resist flow. What changes the viscosity of a fluid? Let’s take a look.
What is the connection with those three factors and explosive eruptions?
Why Explosive? Silica rich magma = high viscosity Highly viscous magma traps gasses. Trapped gas = high pressure in magma chamber. Eventually the pressure is too much and the vent is fractured and all of the rocks are ejected as pyroclastic material.
Rhyolitic magma Highly viscous Found at subduction zones because the magma comes from melted crust. Can lead to a caldera.
Andesitic Magma Medium Viscosity Volcanoes of andesite have both pyroclastic material and thick lava flows. Over time the pyroclastic flow and lava create layers = stratovolcano.
Basaltic Magma Low viscosity Move through the vents very easily. Gasses escape easily. Associated with divergent boundaries. Tend to form thin layers of lava.
Water and Magma Explosion Common on islands with volcanoes. Steam in magma expands rapidly Erupts with great force Krakatoa 1883.
Lava Types High Viscosity = slow flow Block lava formed
Lava Types Low Viscosity = fast flow, Pillow lava formed
Let’s examine our lab. Which lava had the greatest silica content? Rhyolite Which lava had the greatest viscosity? Which lava was most resistant to releasing gas?