﻿THE 
  1942 
  ERUPTION 
  OF 
  MAUNA 
  LOA, 
  HAWAII 
  1 
  

  

  By 
  Gordon 
  A. 
  Macdonald 
  

  

  Geological 
  Survey, 
  U. 
  8. 
  Department 
  of 
  the 
  Interior 
  

  

  Honolulu, 
  T. 
  H. 
  

  

  [With 
  2 
  plates] 
  

   INTRODUCTION 
  

  

  Mauna 
  Loa 
  volcano, 
  on 
  the 
  island 
  of 
  Hawaii, 
  is 
  probably 
  the 
  

   largest 
  and 
  most 
  active 
  volcano 
  in 
  the 
  world. 
  It 
  rises 
  to 
  a 
  height 
  of 
  

   13,680 
  feet 
  above 
  sea 
  level, 
  and 
  some 
  30,000 
  feet 
  above 
  the 
  surrounding 
  

   ocean 
  floor. 
  On 
  the 
  north 
  and 
  northwest 
  its 
  great 
  lava 
  shield 
  abuts 
  

   against 
  the 
  dormant 
  or 
  extinct 
  volcanoes 
  of 
  Mauna 
  Kea 
  and 
  Hualalai, 
  

   and 
  on 
  its 
  southeastern 
  slope 
  rests 
  the 
  smaller, 
  younger 
  shield 
  of 
  

   Kilauea 
  volcano 
  (fig. 
  1). 
  

  

  Mauna 
  Loa 
  is 
  a 
  broad, 
  basaltic 
  shield 
  volcano 
  transected 
  by 
  three 
  

   great 
  series 
  of 
  fractures, 
  known 
  as 
  rift 
  zones, 
  which 
  intersect 
  at 
  the 
  

   summit 
  in 
  the 
  caldera 
  of 
  Mokuaweoweo. 
  Along 
  them 
  have 
  taken 
  place 
  

   most 
  of 
  the 
  innumerable 
  eruptions 
  which 
  built 
  up 
  the 
  mountain. 
  One 
  

   rift 
  zone 
  extends 
  from 
  the 
  summit 
  southwestward 
  to 
  the 
  southern 
  

   point 
  of 
  the 
  island. 
  Another 
  extends 
  northeastward 
  toward 
  the 
  city 
  

   of 
  Hilo, 
  and 
  a 
  third, 
  less 
  prominent 
  one 
  trends 
  northwestward 
  toward 
  

   Hualalai 
  volcano. 
  The 
  rift 
  zones 
  are 
  marked 
  on 
  the 
  surface 
  by 
  many 
  

   cinder 
  cones, 
  spatter 
  cones, 
  pit 
  craters, 
  and 
  open 
  fissures. 
  

  

  Throughout 
  recorded 
  history, 
  Mauna 
  Loa 
  has 
  erupted 
  on 
  an 
  average 
  

   of 
  once 
  every 
  3.6 
  years, 
  but 
  the 
  frequency 
  of 
  eruption 
  may 
  actually 
  

   be 
  somewhat 
  greater 
  owing 
  to 
  the 
  possibility 
  of 
  small 
  summit 
  erup- 
  

   tions 
  having 
  escaped 
  notice 
  during 
  the 
  earlier 
  part 
  of 
  the 
  period 
  of 
  

   occupation 
  of 
  the 
  island 
  by 
  white 
  men. 
  During 
  the 
  110 
  years 
  since 
  

   the 
  first 
  recorded 
  eruption, 
  in 
  June 
  1832, 
  Mauna 
  Loa 
  has 
  been 
  in 
  ac- 
  

   tivity 
  approximately 
  2,527 
  days, 
  or 
  6.3 
  percent 
  of 
  the 
  time. 
  Flank 
  

   eruptions 
  occupied 
  about 
  3.3 
  percent 
  of 
  the 
  total 
  elapsed 
  time, 
  and 
  

   eruptions 
  in 
  and 
  near 
  the 
  summit 
  caldera 
  occupied 
  3 
  percent 
  of 
  the 
  

   time. 
  

  

  1 
  Published 
  by 
  permission 
  of 
  the 
  Director, 
  Geological 
  Survey, 
  U. 
  S. 
  Department 
  of 
  the 
  

   Interior. 
  Reprinted 
  by 
  permission 
  from 
  the 
  American 
  Journal 
  of 
  Science, 
  vol. 
  241, 
  No. 
  4, 
  

   April 
  1943. 
  

  

  199 
  

  

  