﻿ERUPTION 
  OF 
  MAUN 
  A 
  LOA 
  — 
  MACDONALD 
  201 
  

  

  observations 
  used, 
  other 
  than 
  those 
  of 
  the 
  writer, 
  were 
  made 
  by 
  the 
  

   personnel 
  of 
  the 
  Hawaiian 
  Volcano 
  Observatory 
  and 
  Hawaii 
  National 
  

   Park, 
  and 
  the 
  writer 
  wishes 
  to 
  thank 
  all 
  those 
  who 
  contributed 
  in- 
  

   formation 
  for 
  their 
  generous 
  cooperation. 
  Special 
  thanks 
  are 
  due 
  

   Lt. 
  P. 
  E. 
  Schulz 
  for 
  his 
  description 
  of 
  the 
  front 
  of 
  the 
  flow. 
  R. 
  H. 
  

   Finch, 
  Director 
  of 
  the 
  Hawaiian 
  Volcano 
  Observatory, 
  H. 
  T. 
  Stearns 
  

   of 
  the 
  U. 
  S. 
  Geological 
  Survey, 
  and 
  C. 
  K. 
  Wentworth 
  of 
  the 
  

   Honolulu 
  Board 
  of 
  Water 
  Supply, 
  have 
  kindly 
  read 
  and 
  criticized 
  

   the 
  manuscript. 
  James 
  Y. 
  Nitta 
  prepared 
  the 
  illustrations. 
  

  

  PREDICTION 
  OF 
  THE 
  ERUPTION 
  

  

  The 
  1942 
  eruption 
  of 
  Mauna 
  Loa 
  was 
  predicted 
  by 
  R. 
  H. 
  Finch 
  

   several 
  months 
  in 
  advance, 
  on 
  the 
  basis 
  of 
  seismic 
  activity, 
  coupled 
  

   with 
  the 
  known 
  periodicity 
  of 
  the 
  volcano. 
  On 
  February 
  8, 
  1942, 
  

   a 
  strong 
  earthquake 
  occurred 
  on 
  the 
  line 
  of 
  the 
  northeast 
  rift 
  zone 
  

   near 
  Hilo, 
  at 
  a 
  depth 
  of 
  27 
  miles. 
  2 
  This 
  was 
  followed 
  by 
  a 
  series 
  of 
  

   quakes 
  which 
  migrated 
  up 
  the 
  northeast 
  rift, 
  across 
  the 
  summit, 
  and 
  

   a 
  short 
  way 
  down 
  the 
  southwest 
  rift, 
  then 
  returned 
  across 
  the 
  summit 
  

   and 
  settled 
  in 
  the 
  northeast 
  rift. 
  The 
  seismic 
  activity 
  will 
  be 
  de- 
  

   scribed 
  in 
  detail 
  by 
  Finch 
  in 
  another 
  paper. 
  

  

  In 
  memoranda 
  for 
  the 
  Superintendent 
  of 
  Hawaii 
  National 
  Park, 
  

   dated 
  March 
  1 
  and 
  5, 
  1942, 
  later 
  published 
  in 
  the 
  local 
  newspapers, 
  

   Finch 
  called 
  attention 
  to 
  the 
  growing 
  uneasiness 
  of 
  Mauna 
  Loa, 
  

   indicated 
  both 
  by 
  earthquakes 
  and 
  the 
  accumulation 
  of 
  easterly 
  tilt 
  

   at 
  the 
  Volcano 
  Observatory. 
  Easterly 
  tilt 
  has 
  long 
  been 
  known 
  to 
  

   indicate 
  tumescence 
  of 
  Mauna 
  Loa 
  accompanying 
  the 
  rise 
  of 
  magma 
  

   pressure 
  preceding 
  eruption. 
  In 
  a 
  memorandum 
  dated 
  April 
  10 
  he 
  

   wrote, 
  "The 
  progressive 
  splitting 
  of 
  the 
  northeast-southwest 
  rift 
  of 
  

   Mauna 
  Loa 
  that 
  was 
  pronounced 
  in 
  February 
  continued 
  in 
  March 
  

   * 
  * 
  * 
  If 
  Mauna 
  Loa 
  erupts 
  within 
  the 
  next 
  several 
  months, 
  as 
  

   seems 
  probable, 
  the 
  indications 
  point 
  to 
  a 
  flank 
  eruption 
  from 
  the 
  

   northeast 
  rift." 
  3 
  Although 
  military 
  considerations 
  forbade 
  release 
  

   of 
  the 
  prediction, 
  its 
  value 
  as 
  a 
  contribution 
  to 
  practical 
  volcanology 
  

   remains 
  unimpaired. 
  

  

  DESCRIPTION 
  OF 
  THE 
  ERUPTION 
  

   EARLY 
  SUMMIT 
  ACTIVITY 
  

  

  The 
  eruption 
  commenced 
  on 
  the 
  evening 
  of 
  April 
  26, 
  1942, 
  with 
  

   activity 
  along 
  a 
  fissure 
  that 
  opened 
  part 
  way 
  up 
  the 
  cliffs 
  on 
  the 
  west- 
  

   ern 
  side 
  of 
  Mokuaweoweo 
  caldera 
  and 
  across 
  the 
  smaller 
  pit 
  crater, 
  

  

  2 
  Pinch, 
  R. 
  H., 
  personal 
  communication. 
  

  

  'Finch, 
  R. 
  H., 
  Memorandum 
  to 
  the 
  Superintendent 
  of 
  Hawaii 
  National 
  Park, 
  April 
  10, 
  

   1942. 
  

  

  