GEOLOGY

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Assessing  volcanic  hazards   Deciding  where  to  live  requires  careful  consideration.    An  overriding  factor  is  whether  a   place  is  safe.    In  this  exercise  you  will  investigate  a  volcanic  island  to  determine  what   types  of  eruptions  have  occurred  and  what  places  have  the  lowest  and  highest  risk.     Goals:    

• Observe  the  physical  characteristics  of  the  volcano  and  the  rock  types  around  it   • Use  your  observations  to  determine  what  type  of  volcano  is  present  and  how  it  

would  likely  erupt   • Assess  the  potential  for  volcanic  hazards  in  different  parts  of  the  island  and  

determine  the  least  dangerous  place  to  live     Grading:   Point  allotments  are  given  for  each  question.    There  will  be  no  partial  credit.    Your   statements  will  be  graded  on  quality  of  explanation.    Statements  must  be  supported  by   scientific  evidence  given.         Volcano  Erupts!    (a  newspaper  account  of  an  imaginary  volcano)    

The  Summit  volcano  began  erupting  in  early  September  of  1952,  and  dozens  of   small  eruptions  have  occurred  since  that  time.    For  10  years  before  the  1952  eruption,   residents  of  the  area  observed  plumes  of  white  steam  rising  from  the  summit  of  the   crater.    In  the  summer  of  1952,  local  inhabitants  reported  an  increase  in  the  output  of   steam,  an  increased  smell  of  sulfur,  and  a  series  of  small  earthquakes.         The  first  eruption  was  a  single  explosive  burst  that  lasted  about  three  hours   and  that  was  accompanied  by  clouds  of  ash  that  rose  kilometers  into  the  air.    Heavy   ash  fell  around  the  volcano,  and  a  light  dusting  of  ash  was  reported  on  adjacent   islands  up  to  20  kilometers  away.    The  eruption  melted  snow  and  ice  high  on  the   crater,  forming  a  mudflow  that  moved  along  stream  channels  and  inundated  many   areas  in  valleys  downstream  from  the  volcano.    After  the  main  eruption  a  lava  dome   started  growing  in  the  crater.       All  subsequent  eruptions  have  been  smaller  and  of  a  different  style.    They  have   been  similar  to  one  another.    In  each  eruption,  a  cloud  of  ash  and  rocks  moves  rapidly   downhill.    After  each  eruption,  geologists  noted  that  one  side  of  the  dome  in  the  crater   had  collapsed  into  a  pile  of  ash  and  rocks.              

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Instructions   Write  your  answers  on  the  map  where  appropriate.    Other  answers  should  be  recorded   on  the  back  of  the  map.    You  may  use  your  notes  and  the  textbook.    

  A. (5  pts)  Read  the  newspaper  account  of  this  volcano’s  eruption  history.    On  the  

diagram,  put  the  eruption  events  in  order  from  first  to  last:   • Lava  dome  growth   • Lava  dome  collapse  and  pyroclastic  flows   • Steam  eruptions   • Lahar   • Sub-­‐Plinian  eruption   • Small  earthquakes  accompanied  with  sulfuric  fumaroles  (gas  emissions)  

B. (1  pt)  What  type  of  volcano  is  this?  (write  on  the  map)     C. (3  pts)  Label  the  parts  of  the  volcano  on  the  diagram.  

• Crater   • Lava  dome   • Flank  (the  sides  of  the  volcano)  

D. (3  pts)  Label  the  rocks  1,  2,  &  3  with  the  proper  rock  types   • Dacite   • Old  pyroclastic  flow  deposits   • Young  pyroclastic  flow  deposits  

E. (3  pts)  Assess  how  each  volcanic  feature  contributes  to  the  hazard  potential  in   different  parts  of  the  island.    On  the  map,  draw  boundaries  around  and  label  those   areas  that  have  high,  medium,  or  low  hazard  potential  compared  to  the  rest  of  the   island.    The  differences  between  the  three  hazard  zones  will  be  fairly  subjective.    Use   your  best  judgment  and  be  consistent.  

a. To  draw  boundaries,  divide  the  island  into  three  parts  emanating  from  the   summit  of  the  volcano  (like  slicing  a  pie).  Label  each  part  with  its  hazard  risk   –  high,  medium,  or  low.      

F. (3  pts)  Write  a  statement  that  supports  your  choices  of  high,  medium,  and  low   hazards.    

G. (1  pt)  Identify  the  area  you  consider  to  be  the  safest  place  to  live  with  an  X  on  the   map.    When  choosing  between  two  sites  that  are  equally  safe,  you  may  consider   other  factors,  such  as  the  scenery,  whether  the  sites  are  level  enough  to  build  on   safely  or  easily  accessible,  and  whether  they  are  subject  to  storms,  landslides,   floods,  and  other  natural  hazards.  

H. (1  pt)  Write  a  statement  that  supports  your  choice  of  the  safest  place.    

Name: ______________________________ Sec: ________

Rock 2 is hard igneous rock that contains pumice and ash

Rock 3 is composed of loose pumice and as deposited in a low lying area

Rock 1 is composed of

F1. High hazard zone explanation:

F2. Medium hazard zone explanation:

F3. Low hazard zone explanation:

H. Safest Place (marked with an X on your map):