CEE 1030 1nd Edition Lecture 4 Volcanoes and Other Igneous Activity Outline of Last Lecture I Igneous rocks magma and lava a Nature of magma lava II Classifying igneous rocks III Igneous textures IV Minerals in igneous rocks a Examples V Viscosity and the origins of magma VI Review rocks in Iowa and ore Outline of Current Lecture I Volcano resources II Nature of volcanic eruptions III Types of volcanic deposits a Basaltic lava flow types IV Basaltic volcanoes V Intermediate rhyolitic volcanoes VI Pyroclastic falls and flows VII Lahars VIII Volcanoes and climate IX Intrusive igneous activity X Hydrothermal systems XI Massive intrusions batholiths Current Lecture I II Volcano resources a How volcanoes work geology sdsu edu how volcanoes work b Volcanic hazards volcanoes usgs gov c Volcanoes of the world volcano si edu world d Review effusive lava flow vs explosive eruption i Magma composition temperature gas content are all factors Nature of volcanic eruptions a Factors above control viscosity of magma b Measures material s resistance to flow c Temperature i Hotter magmas less viscous These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute III IV V d Composition i High SiO2 content high viscosity e Dissolved gases i Violence of eruption is related to how easily the gases escape from magma depends on viscosity ii With sticky magma bubbles get trapped when magma gets closer to the surface the bubbles explode Types of volcanic deposits a Non explosive eruptions lava flows b Explosive eruptions pyroclastic deposits c Basaltic lava flow types i Pahoehoe ropy texture plasticky ii Aa rough blocky jagged texture iii Pahoehoe changes to aa with a loss of gas and temperature increasing the viscosity d 70 of lava s volume erupted at Earth s surface every year occurs underwater at mid oceanic ridges this is called submarine eruptions Basaltic volcanoes a Shield volcano large broad circular shape with gentle dipping slopes i Built by successive fluid lava flows from a central vent ii Flows travel long distances b Cinder cones aka scoria cones built from ejected gas rich lava fragments i Steep slope angle of loose cinders c Fissure eruptions alignment of cinder cones fissures under the earth d Flood basalt plateaus huge stacks of thick fissure fed basalt lavas e Pyroclastic material frothy gas rich vesicular texture i Basaltic scoria or cinders ii Intermediate rhyolitic pumice Intermediate rhyolitic volcanoes a Composite cones or stratovol canoes i Classic volcano profile ii Interbedded lava flows and pyroclastic debris iii Potentially the most dangerous volcano type 1 Doesn t have much structural integrity 2 Water inside the volcano has the potential to trigger a massive destruction of the volcano b Caldera ex Crater Lake OR something triggers an eruption in buried magma the earth below the volcano collapses downward c Lava dome SiO2 rich lava is very viscous can hardly flow thick lava is squeezed out of the vent like toothpaste d Mt St Helens 1980 i Largest eruption in historic times in the U S ii Summit was lowered by more than 400 m VI VII VIII IX X XI iii Over 1 km cubed of ash and rock debris was emptied iv Pressure of the magma created a bulge in the side of the volcano causing the side to burst and explode Pyroclastic falls and flows a Pyroclastic material falls from eruption and a cloud of material is explosively ejected from the vent b Pyroclastic flows are gravity controlled surface flows from collapse of eruption column or lava dome i Flows are the most deadly of all volcanic phenomena ii Fluidized mix of semi solid rock fragments and hot expanding gases that flow quickly down the volcano flank c Pyroclastic material i Rapid expansion of gas bubbles results in obliteration and fragmentation of magma and rock ii Pyroclastic fire fragments Lahars a Volcanic mud flows b Mixture of volcanic debris and water i Eruption triggered melting of snow and glaciers ii Heavy rainfall also can saturate loose ash deposits iii Deadly and fast Volcanoes and climate a April 1815 eruption of Mt Tambora Indonesia i Largest eruption in historic times ii Volcanic ash injected into stratosphere gave way to fantastic sunsets iii The gas reflects sunsets and reduces heat from the sun iv This explains the historic 1816 the year without sunlight Intrusive igneous activity a Over 80 of magma produced never reaches Earth s surface cool and solidify to intrusions b Intrusion types i Shape tabular sheetlike vs massive ii Orientation with respect to the host surrounding rock c Tabular intrustions dikes and sills i Dike discordant cuts across layers in country rock ii Sill concordant parallel to layers in country rock Hydrothermal systems a Circulation of water around a magma chamber b Leaches elements from surrounding rocks c Can form economically important metal ores Massive intrusions batholiths a Batholith largest intrusions cover areas of more than 100 km squared b Made of smaller intrusions called stocks or plutons c Coarse grained granites