Ees 1030 1st Edition Lecture 4Current LectureVolcanoes and other Igneous Activity:What controls how explosive a volcanic eruption is?- Magma silica, water vapor, and gas content.- These 3 factors determine whether a volcano will have an effusive lava flow or anexplosive eruption.All these factors control the viscosity of magma. Viscosity: this is a measure of a materials resistance to flow.- Temperature plays an important role in this because the hotter the magma the more viscous it is. - Silica content is also a determining factor for how explosive an eruption will be. - Volcanos that are high in silica have a high viscosity. This means they will produceexplosive eruptions because gas cannot be released as quickly and causes pressure to build. Felsic magmas are an example.- Magma that are low in silica have a low viscosity. This means that lava will flow more because gases are easily released. Basaltic and intermediate lava flows:- Non explosive eruptions. - Basaltic flows: Pahoehoe flow - smooth billowy and ropy flow. Behaves like a plastic. - Ropey pahoehoe: lava flows under a plastic like skin and bunches into wrinkles. - Aa: lava flow is fragmented and rough with a spiny appearance. - Basaltic flows travel very fast Basaltic volcanoes: - Shield volcano: large broad circular shape with gentle slopping sides. Made from fluid lava flows from a central vent. - Ash or Cinder-cone volcano: formed from pyroclastic rock or cinders erupting that build into a steep hill with a crater on the top.Pryoclastic material: frothy, gas rich material that is very porous. Greater than 60% vesicles or voids (bubbles). - Volcanic ash, Obsidian, pumice, volcanic tuff, etc are all pyroclastic material. Pyroclastic=fire fragments.- Ash <2 mm- Lapilli 2-64 mm- Bombs >64 mmLahars: volcanic mud flow.- When a volcano erupts ice and snow are melted by the heat and the water carries ash and other things down the volcano causes a mudflow. Also can be caused by heavy rainfall onto loose ash. Volcanoes and Climate:- Gases and other particles are put into the atmosphere during eruptions. This can warm or cool the earth surface because it interferes with sunlight reaching earth.Igneous activity:Dike: magma beneath the surface that goes through sedimentary layers. Sill: magma that goes between sedimentary layersBatholith: forms from deep down cooled magma in earth’s crust. Made of smaller intrusions called stocks or plutons. Discordant: dikes, they cut into country rockConcordant: sills, are parallel with the country