﻿ERUPTION 
  OF 
  MAUNA 
  LOA 
  — 
  MACDONALD 
  211 
  

  

  and 
  where 
  the 
  levee 
  was 
  unusually 
  narrow. 
  The 
  levee 
  was 
  broken, 
  

   and 
  a 
  small 
  lava 
  stream 
  escaped 
  to 
  one 
  side 
  of 
  the 
  main 
  flow, 
  but 
  the 
  

   topographic 
  depression 
  that 
  had 
  guided 
  the 
  original 
  flow 
  also 
  guided 
  

   the 
  new 
  branch. 
  It 
  flowed 
  parallel 
  to 
  the 
  main 
  river 
  for 
  a 
  short 
  

   distance, 
  and 
  then 
  rejoined 
  it. 
  

  

  Although 
  the 
  bombing 
  had 
  no 
  effect 
  in 
  stopping 
  the 
  flow, 
  it 
  did 
  

   demonstrate 
  that 
  under 
  favorable 
  circumstances 
  it 
  might, 
  by 
  breaking 
  

   down 
  the 
  levees, 
  be 
  possible 
  to 
  create 
  new 
  branches 
  of 
  a 
  flow 
  and 
  

   thus 
  retard 
  the 
  advance 
  of 
  the 
  main 
  front. 
  Total 
  diversion 
  of 
  the 
  

   flow 
  would, 
  however, 
  depend 
  on 
  a 
  combination 
  of 
  favorable 
  circum- 
  

   stances, 
  including 
  a 
  lava 
  river 
  flowing 
  in 
  a 
  channel 
  higher 
  than 
  the 
  

   surrounding 
  territory, 
  narrow 
  levees 
  that 
  could 
  be 
  broken 
  down 
  by 
  

   bombing, 
  and 
  topography 
  that 
  would 
  direct 
  the 
  new 
  flow 
  away 
  from 
  

   the 
  old 
  one 
  rather 
  than 
  back 
  into 
  it. 
  The 
  necessity 
  for 
  further 
  

   bombing 
  was 
  removed 
  by 
  the 
  stagnation 
  of 
  the 
  principal 
  flow 
  a 
  few 
  

   days 
  later. 
  

  

  There 
  appear 
  to 
  be 
  three 
  manners 
  in 
  which 
  bombing 
  may 
  cause 
  

   the 
  formation 
  of 
  new 
  branch 
  flows, 
  and 
  thus 
  lessen 
  or 
  terminate 
  the 
  

   advance 
  of 
  the 
  previous 
  lava 
  front. 
  One 
  of 
  these 
  involves 
  the 
  break- 
  

   ing 
  down 
  of 
  a 
  narrow 
  levee 
  along 
  an 
  open 
  lava 
  river, 
  as 
  was 
  done 
  

   in 
  the 
  1942 
  eruption. 
  Another 
  and 
  similar 
  method 
  is 
  the 
  breaking 
  

   down 
  of 
  part 
  of 
  the 
  cone 
  wall, 
  allowing 
  lava 
  to 
  escape 
  laterally 
  and 
  

   form 
  a 
  new 
  flow, 
  as 
  it 
  did 
  naturally 
  during 
  the 
  1942 
  eruption, 
  on 
  

   May 
  4. 
  The 
  third 
  method 
  involves 
  the 
  breaking 
  in 
  of 
  the 
  roof 
  of 
  

   a 
  lava 
  tube 
  through 
  which 
  the 
  lava 
  river 
  is 
  flowing. 
  This 
  may, 
  if 
  the 
  

   roof 
  of 
  the 
  tube 
  is 
  thick 
  enough, 
  block 
  the 
  tube 
  with 
  solid 
  fragments, 
  

   or 
  it 
  may 
  cause 
  local 
  congealment 
  of 
  the 
  lava, 
  perhaps 
  partly 
  or 
  en- 
  

   tirely 
  through 
  violent 
  stirring 
  by 
  the 
  explosions 
  resulting 
  in 
  local 
  

   change 
  of 
  the 
  flowing 
  lava 
  from 
  pahoehoe 
  to 
  aa. 
  The 
  local 
  congeal- 
  

   ment 
  may 
  plug 
  the 
  tube, 
  resulting 
  in 
  the 
  development 
  of 
  a 
  new 
  lava 
  

   river. 
  This 
  appears 
  to 
  have 
  happened 
  as 
  a 
  result 
  of 
  the 
  bombing 
  of 
  

   the 
  1935 
  lava 
  flow, 
  14 
  but 
  was 
  not 
  to 
  be 
  expected 
  in 
  the 
  1942 
  eruption, 
  

   where 
  the 
  lava 
  river 
  was 
  open, 
  not 
  enclosed 
  in 
  a 
  tube. 
  

  

  It 
  appears 
  to 
  the 
  writer 
  very 
  doubtful 
  if 
  bombing 
  would 
  ever 
  cause 
  

   the 
  termination 
  of 
  an 
  eruption. 
  Its 
  value 
  probably 
  lies 
  only 
  in 
  the 
  

   possibility 
  of 
  delaying 
  the 
  advance 
  of 
  the 
  main 
  flow 
  front, 
  by 
  causing 
  

   the 
  formation 
  of 
  new 
  lateral 
  flows, 
  or 
  with 
  very 
  favorable 
  topography 
  

   by 
  deflecting 
  the 
  flow 
  into 
  new 
  channels. 
  

  

  CONCLUSIONS 
  

  

  The 
  1942 
  eruption 
  of 
  Mauna 
  Loa 
  opened, 
  like 
  most 
  others, 
  with 
  

   activity 
  in 
  and 
  near 
  the 
  summit 
  caldera. 
  The 
  principal 
  activity, 
  a 
  

  

  14 
  Jaggar, 
  T. 
  A., 
  The 
  Volcano 
  Letter, 
  No. 
  431, 
  January 
  1936, 
  and 
  No. 
  465, 
  July-September 
  

   1939. 
  

  

  