[Geysers] More About Nonsense

[Carlton Cross]

This is a relay from Ron Keam.  (Because the Internet gods were in a bad mood when his original was launched.)
Carlton Cross
Alternate Moderator


From: Ron Keam <r.keam at auckland.ac.nz 
Subject: Re: [Geysers] More About Nonsense

I thoroughly endorse Carlton's explanation as to why (in most cases) it is a pressure drop, rather than a pressure rise, that triggers the eruption of a geyser.

However, list eaders might be interested in a case where a different mechanism seems to have applied. The exception was the situation in Wairoa geyser (now inactive) at Whakarewarewa in New Zealand.  In the early 1900s this geyser had calmed down from a period of natural eruptions that followed on from disturbances triggered partly by the 1886 Tarawera eruption, and required artificial triggering.  It was very spectacular (about 200 feet) and was soaped for special occasions, and the local populace and eminent visitors were treated to this spectacle.  But it took about twenty minutes after soaping before the eruption commenced.  This is in contrast to the one or two minutes that it takes Lady Knox Geyser at Waiotapu to respond. I believe that in the case of Wairoa the mechanism was slightly unusual.  The geyser has a narrow throat, and, when it was able to be triggered, water level sat churning more or less vigorously and oscillating gently about 4 to 5 feet below the lip.  Such meant that the region of the water filled part of the vent where the churning was occurring would have an approximately uniform temperature, and this temperature would clearly have been slightly below the boiling temperature except right near the top of the water.  When soap was introduced, the vent above the water surface quickly filled with a mass of soap-suds, and thus it remained, with occasional upward surges of suds, for the twenty minutes.  In my opinion the suds formed an "insulating layer" above the water surface, reducing the churning and preventing the previously steadily boiling water from releasing the steam directly into the atmosphere, and thus trapping the heat within the suds and the water below.  The reduced churning would allow temperatures to rise gradually in the top of the water column within the vent.  Eventually water would reach boiling temperature at lower depths in the column, and when sufficiently vigorous boiling resulted there, projecting water out, pressures further down still would momentarily reduce, and the runaway eruption would be initiated.  So, Wairoa, I think, is an example of heat-trap triggering.  (It is an interesting fact that when it was 
soaped very little of the (sudsy) water was expelled from this geyser before the eruption started.)

Ron Keam