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UID:3508
LOCATION:Seattle Town Hall
DTSTAMP:20151027T183000
DTSTART:20151027T183000
DTEND:20150529T200000
SUMMARY:Public Lecture: Fire and Ice: Volcanoes\, Earth Structure\, & 
 the Evolution of the Antarctic Ice Sheet
DESCRIPTION:Dr. Doug Wiens\n\nThe continent of Antarctica supports the lar
 gest ice sheets in the world. The history of the ice sheets 
 is intertwined with the geological history of continent\, inv
 olving processes such as mountain building\, the response of 
 the land to the weight of glaciers\, and heat flow melting an
 d lubricating the bottom of the ice sheet. Very little is kn
 own about the history of Antarctica because the ice sheets p
 reclude the usual geological sampling and mapping\, so seismo
 logy offers a method to “see through the ice” and unders
 tand the continent beneath. Recent advances in technology no
 w allow autonomous seismographs to be deployed across the co
 ntinent for the first time.\n\nIn this presentation I will dis
 cuss projects that are installing seismographs across Antarc
 tica and summarize recent discoveries. New results reveal th
 at East Antarctica represents an ancient continent\, with an 
 average geological age of greater than one billion years and
  with highlands supported by thick continental crust.  In c
 ontrast\, West Antarctica shows evidence of recent tectonic a
 ctivity\, and high heat flow that may lubricate the base of t
 he ice sheet. The seismographs record earthquakes from magma
  movement associated with volcanoes beneath the ice. The hig
 h mantle temperatures suggest low mantle viscosity\, such tha
 t the response of the land to ice mass changes will occur wi
 thin a few hundred years. These insights are changing the wa
 y we model the recent history of the ice sheet.\n\nSeismograms
  also provide important constraints on the movement and forc
 es acting on the ice sheets. “Icequakes” ranging from ve
 ry small cracking events near the surface of the ice sheet t
 o massive crevassing and calving episodes produce unique sei
 smic signals that help reveal the physics of ice movement. T
 he largest signals come from a unique region on the Whillans
  Ice Stream\, where a 100 mile-long section of the ice stream
  lurches forward twice a day\, triggered by ocean tides\, and 
 sending seismic waves traveling across the entire continent.
  This unusual behavior may signal the slowing down of this i
 ce stream in response to changes in the amount of water alon
 g the ice stream bed.
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