GEOL 108Lg 1st Edition Lecture 8Outline of Last LectureI. Physics and Geology of VolcanoesII. Effusive vs. Explosive VolcanoesOutline of Current LectureI. Volcanic Hazardsa. Pyroclastic Flows, Ash Clouds, EtcCurrent LectureVolcanoes IIEarthquake that occured in the Indian Ocean triggered number of earthquakes that were above magnitude 5.5.. These earthquakes were triggered in regions where the surface waves do most of the shaking. Mag. 8.6, Mainshock right lateral - large earthquakes happened within 6 days of that main shock. This is important because it gives scientists some indication of global earthquake triggering. This partcular earthquake, a large strike slip earthquake, triggered the most earthquakes ever recorded - before quake, relatively few 6-7 so a lot of the areas had built up tension and were ready to go - earthquake came at the right time to trigger significant earthquakes worldwide. The strange thing here is that it was REALLY big. Distributed deformation (earthquakes all over the place). The surface waves cause large damage - direct ground shaking effect.Hazards associated with VolcanoesTephra is the term for the rock particles that are mixed in the eruption cloudEruption column comes down side of volcano, it flows pyroclastic flow (hot gases, rockmaterial).One of the more prominent and spectacular volcanic hazards is the pyroclastic flow.Pyroclastic Flow: what the volcano “spits out” - a fluidized mixture of solid and semi-solid fragments + hot, expanding gases that flow down the flank of a volcano. It movesmuch like an avalanche would, but rather its contents are extremely hot and contain toxic gases. They are more deadly if they are a lateral blast.The eruption of a volcano can drastically alter the environment surrounding the volcano, even for extended periods of time post-eruption. They can alter land and water around theimmediate volcanic area, but also the sulfuric acid emmited into the stratosphere has thecapability to temporarily alter the area’s climate. The eruption of a volcano forces many peoplein its immediate surrounding area to abandon their homes – even those who live far away, while their homes may not be destroyed, will feel the effects of a volcanic eruption with damages caused by flooding, ash, tephra, and lahars. Volcanoes are quite predictable, and if they are analyzed in enough time, citizens in their surrounding areas can be forewarned.T h e d e a t h t oll of Vol c a n o es-500 million people living near volcanoes-Almost 100,000 deaths during the last 125 years-23,000 lives lost in the last 20 years-Densely populated countries in the volcanic zones-Some major cities (<350,000 people located near volcanoes) the northwest, indonesiaAsh clouds affect the state of global climate . Volcanoes in Hawaii of course has been erupting continuously. Many speculated for quite some time about the source of the hot springs in Yellowstone, and finally it was concluded that the entire area was a collapsed volcano.H o t s p o t V o l c a n oA hotspot volcano (pictured) erupts from fissures. Gentle lava flows in large quantities after the initial release of gas, as pictured below.Subduction zone magmas are richer in silica; thicker and pastier; plugs up volcano; also rich in water content – as it rises, water vapor comes out.Ex p losive V ol c a n oes: E R UP T I O N T Y P E SVULCANIAN is a brief Explosion - as opposed to a PLINIAN which is sustained. CALDERA is the collapse the occurs at times after PLINIAN.Mt St HelensWe have a fairly well documented history of how the details of the explosion transpired - initially, there were geodatically dectected ground deformations underneath the volcano. Mt. St. Helens - seismigraph from Mt. St. Helens (tremors ) - dynamics of the volcanic vent, you have a bunch of them regularly (days leadingup to eruption) increased activityBulging and volcanic tremors - indicators for eruptionsMt St Helens, its stages:F o re c as t i n g Vol c a n ic Act i vity-Seismic activities – earthquakes as indicators of Volcanic Activity-Thermal magnetic and hydrologic conditions-amount of volcanic gas emission, both the rate and composition.-topography, tilting and bulging-Gps receivers record deformation: monitor the volcanoVolcanoes in Iceland that go along mid oceanic ridge sectionKatla: 50/100+ bigger than Eyjafjallajökull,, typically it goes next afer Eyjafjallajökull, which exploded in 2010. Many fear an ash cloud going up into atmosphere – caused problems with flights.Ash clouds are hazardous for air traffic, move at speeds of up to 100 km/h, block away solar radiation and are harmful to human healthMt Unzen 1991 (one of 19 active volcanoes in japan)Several ash flows by the end of 1993 - geting the dubious honor of the “king of ash flow” centers. 44 people killed including Harry Glicken a volcanologist and escaped death of Mt St Helens, died in the Unzen eruption.A review:Lava flow: From the vent of a crater or along a line of fissureMost common and abundant type: Basaltic lava lowPahoehoe lava: Less viscous, higher temp, with a smooth ropy surface textureA’a lava: More viscous and slow moving, lower temp, with a blocky surface