﻿ERUPTION 
  OF 
  MAUNA 
  LOA 
  — 
  MACDONALD 
  203 
  

  

  During 
  the 
  day 
  the 
  fissure 
  gradually 
  lengthened 
  down 
  slope, 
  its 
  

   course 
  changing 
  to 
  N. 
  70° 
  E., 
  and 
  by 
  3 
  p. 
  m. 
  the 
  total 
  length 
  of 
  the 
  

   erupting 
  fissure 
  was 
  about 
  a 
  mile. 
  Fountains 
  were 
  active 
  along 
  both 
  

   its 
  upper 
  and 
  lower 
  ends. 
  Along 
  its 
  middle 
  part 
  lava 
  welled 
  forth 
  

   copiously, 
  forming 
  a 
  lava 
  river 
  which 
  followed 
  the 
  course 
  of 
  the 
  fis- 
  

   sure. 
  Along 
  this 
  portion 
  of 
  the 
  fissure 
  fountaining 
  was 
  much 
  less 
  

   prominent 
  than 
  elsewhere, 
  but 
  occasional 
  bursts 
  of 
  fountain 
  activity 
  

   through 
  the 
  river 
  suggested 
  that 
  the 
  paucity 
  of 
  fountain 
  activity 
  re- 
  

   sulted 
  from 
  drowning 
  of 
  the 
  fountains 
  by 
  the 
  lava 
  river. 
  Thin 
  flows 
  

   of 
  very 
  gas-rich 
  pahoehoe 
  were 
  poured 
  out 
  on 
  both 
  sides 
  of 
  the 
  rift 
  

   and 
  flowed 
  downhill 
  alongside 
  it, 
  changing 
  to 
  aa 
  half 
  a 
  mile 
  below 
  

   the 
  bend 
  in 
  the 
  fissure. 
  Fountain 
  activity 
  reached 
  a 
  maximum 
  at 
  8 
  

   p. 
  m. 
  on 
  April 
  28, 
  the 
  fountains 
  attaining 
  a 
  height 
  of 
  500 
  feet, 
  or 
  a 
  

   little 
  more. 
  

  

  The 
  fissure 
  along 
  which 
  the 
  lava 
  broke 
  out 
  extended 
  up 
  the 
  mountain 
  

   probably 
  to 
  the 
  summit, 
  and 
  although 
  no 
  lava 
  issued 
  in 
  the 
  zone 
  be- 
  

   tween 
  10,000 
  and 
  12,000 
  feet, 
  fume 
  was 
  observed 
  at 
  several 
  localities. 
  

   Fume 
  was 
  also 
  noted 
  at 
  the 
  source 
  cone 
  of 
  the 
  1935 
  eruption. 
  Lava 
  

   extrusion 
  at 
  the 
  summit 
  decreased 
  greatly 
  on 
  the 
  27th 
  and 
  appeared 
  

   to 
  have 
  stopped 
  when 
  the 
  flank 
  eruption 
  began. 
  Fissuring 
  was 
  later 
  

   found 
  by 
  R. 
  H. 
  Finch 
  also 
  to 
  extend 
  well 
  down 
  slope 
  from 
  the 
  locus 
  

   of 
  the 
  eruption. 
  Several 
  observers 
  reported 
  seeing 
  new 
  lava 
  fountains 
  

   on 
  the 
  northeast 
  rift 
  near 
  the 
  summit 
  late 
  in 
  the 
  afternoon 
  of 
  May 
  1, 
  

   but 
  this 
  reported 
  eruption 
  was 
  probably 
  merely 
  the 
  effect 
  of 
  sunset 
  

   colors 
  on 
  a 
  fume 
  cloud, 
  as 
  it 
  was 
  not 
  visible 
  after 
  dark. 
  Moreover, 
  

   it 
  appears 
  unlikely 
  that 
  once 
  the 
  activity 
  had 
  broken 
  out 
  at 
  9,200 
  feet 
  

   altitude, 
  it 
  would 
  migrate 
  back 
  up 
  the 
  fissure 
  and 
  break 
  out 
  anew 
  at 
  

   or 
  above 
  12,000 
  feet. 
  

  

  Shortly 
  after 
  the 
  outbreak 
  at 
  9,200 
  feet 
  altitude, 
  lava 
  issued 
  at 
  an- 
  

   other 
  locality 
  3 
  miles 
  farther 
  down 
  slope, 
  at 
  an 
  altitude 
  of 
  7,800 
  feet. 
  

   This 
  lower 
  locality 
  had 
  none 
  of 
  the 
  characteristics 
  habitually 
  ex- 
  

   hibited 
  by 
  true 
  vents 
  on 
  Mauna 
  Loa. 
  The 
  lava 
  issued 
  relatively 
  

   quietly 
  from 
  beneath 
  the 
  toe 
  of 
  an 
  older 
  aa 
  flow 
  which 
  overlies 
  a 
  still 
  

   older 
  brown 
  pahoehoe. 
  Fume 
  was 
  liberated 
  in 
  much 
  less 
  volume 
  than 
  

   at 
  the 
  vent 
  at 
  9,200 
  feet, 
  and 
  no 
  lava 
  fountains 
  appear 
  to 
  have 
  been 
  

   present. 
  Only 
  a 
  very 
  small 
  amount 
  of 
  dense 
  spatter 
  was 
  formed, 
  and 
  

   the 
  lava 
  was 
  denser 
  and 
  much 
  poorer 
  in 
  gas 
  than 
  that 
  at 
  the 
  higher 
  

   sources. 
  Steam 
  issued 
  from 
  arcuate 
  fissures 
  which 
  lay 
  at 
  approxi- 
  

   mately 
  right 
  angles 
  to 
  the 
  flow 
  and 
  to 
  the 
  rift 
  zone 
  just 
  above 
  the 
  point 
  

   at 
  which 
  the 
  lava 
  issued. 
  7 
  No 
  traces 
  of 
  fracturing 
  parallel 
  to 
  the 
  rift 
  

   zone 
  could 
  be 
  found. 
  This 
  lower 
  outbreak 
  probably 
  represents 
  lava 
  

   draining 
  through 
  an 
  older 
  pahoehoe 
  tube 
  which 
  intersected 
  the 
  erup- 
  

   tion 
  fissure 
  at 
  some 
  point 
  higher 
  up 
  the 
  mountain. 
  

  

  T 
  An 
  excellent 
  aerial 
  photograph 
  of 
  the 
  lower 
  source, 
  showing 
  these 
  features, 
  has 
  been 
  

   published 
  in 
  Life, 
  vol. 
  12, 
  No. 
  22, 
  p. 
  36, 
  June 
  1, 
  1942. 
  

  

  