Convergent Plate Boundary Geologic Features Ocean Trench Mtn / Volcano New Ocean Crust Old Continenta l Crust Beadle, 2009 Convection cells provide the force to move the continents. The crust is carried on its back. The trench is a result of the denser crust subducting below the less dense crust. The melted rock from the old crust going back into the mantle may be released in a volcano. Zone of Earthquakes ~8-9.0 M
Most of Earth s Mountains & Volcanoes are along convergent plate boundaries
A volcano is any place where magma reaches the surface. This also occurs at divergent plate boundaries. Magma comes up as the plates are pulled apart.
Volcanoes also happen at Hot Spots Briefly explain how volcanoes form at hot spots.
https://www.iris.edu/hq/inclass/animation/hotspot_volcanis m_thermal_plume
How does it work? Ash, Gasses, etc. Overlying Rock Pressure Overlying Rock Pressure is Overcome by internal Pressure Gas Pressure The explosion of a volcano is similar to the soda water bubbling out of a warm bottle of soda pop. Dissolved gases are trapped in magma under pressure. As magma rises, the gasses have less pressure and expand and form bubbles puts pressure on crust eruption. When a volcano erupts, it unleashes a ton of energy.
2 Kinds of Eruptions Quiet Explosive - Dependent upon Silica (SiO 2 ) content in the magma - More silica makes the magma more viscous (thicker and doesn t flow as well) -Viscous magma will cause a bigger explosion.
Quiet Eruptions Low silica makes it flow easier as gasses bubble out gently. It oozes quietly from the vent and can flow for many kilometers. Aa Pahoehoe
Aa High Viscosity lava flow
https://www.youtube.com/watch?v=ypwp5i Ru68I
Low viscosity lava flow Pahoehoe
Explosive Eruptions A volcano erupts explosively if its magma is high in silica. High silica content has more viscosity from chemical bonds breaking and reforming, making it thick and sticky.
Explosive Eruptions High viscosity magma does not always flow out of the crater. Instead, it builds up in the volcanoes pipe, plugging it like a cork in a bottle. Dissolved gases, including water vapor, cannot escape from the thick magma. The trapped gases build up pressure until they explode. The erupting gases and steam push the magma out of the volcano with incredible force.
Rock, minerals and volcanic glass. Can travel thousands of kilometers away from the volcano Ash
Lahar Flow of mud and water. Often caused by volcanic eruptions that melt snow and glaciers. Can travel over 50 m/s, 140 meters thick and be hot or cold https://www.youtube.c om/watch?v=kznwnp NTB6k
Pyroclastic Flow Gases and rock traveling down from the volcano due to gravity. Temperatures can reach 1000 C and travel up to 700 km/hr https://www.youtube.com/watch?v=fllzc1 zkut4
What Types of Energy Do Volcanoes Have? Thermal (Heat) Energy Mechanical Energy Light Energy (Glow & least effective for change) These energies combined change the earth s surface
Are volcanoes predictable?
Top Signs it s Gonna Blow Things we look for when we Monitor Bulging Tilting Increase in Earthquakes Increase in Temperature from underground water
Lava Based Volcanic Landforms Shield Volcanoes Largest volcano Low Silica: Low Viscosity Lava flows gradually builds a wide, gently sloping mountain. Thin layers of lava pour out of a vent and harden on top of previous layers. i.e. Hawaii
Lava Based Volcanic Landforms Cinder Cones Smallest type of Volcano High Silica: High Viscosity Produces ash, cinders and bombs. Materials build up around the vent in a steep, cone shaped hill or small mountain. i.e. Paricutin, Mexico
Lava Based Volcanic Landforms Composite Volcano 2 nd Largest Mix of other two (Medium Silica) Sometimes lava flows alternate with explosive eruptions of ash and cinder. Magma is a mix of Shield & Cinder Tall, cone shaped w/ alternate layers of ash and lava. Mt. St Helens is an example