[Geysers] RE: Conduit dynamics: bottom up or top down?

[Davis, Brian L.]

(Answering several response in a single message)

Jeff Cross wrote:

>> Geyser erupt from the top down.
>
> What about geysers like Artemisia, Great Fountain and Giantess?

Hmm, let me rephrase. My point was I had been assuming that all geysers erupt from the bottom up, with superheating occurring near the base of the conduit. That made sense to me because (a) all the models do it (I know, bad reason), and (b) that’s where the heat source is. As I dug through the literature, I found to my surprise that’s evidently not the case for Old Faithful. There, in situ measurements show that at least just prior to the eruption, only the near surface few meters are near boiling, so *presumably* the eruption starts there.

> The Great Geysir of Iceland is also an example where boiling
> begins at a point well below the surface.  Barth... suggests
> that boiling may start 8-10 meters below the surface.

So clearly in that system (that can be triggered by surfactant) vigorous convection must take place through the conduit to at least that depth. This is something my models at least so far can’t manage. It looks like I’m going to have to scale with respect to the Reynolds and Froude numbers (ugh). Ugh.

> Allen and Day remark... Hot water free to circulate attains
> the superheated state only as it gains higher levels, and
> continues moving till it reaches the surface.  Eruption is
> probably due to boiling in a side chamber.

Which is an interesting thought. It would take a side chamber large enough to release a large enough steam bubble to initiate the eruption.

stepheneide at cableone.net wrote:

> I have to wonder if the reasons your models don’t quite
> behave like geysers is that you are using a point heat
> source

I think ultimately I need to insulate the model conduit much better, but it’s difficult to do safely (since the insulation will be right over the hotplate, I don’t want to risk melting or burning). But the heat source I’m less confident about. Many sources assume the conduit is filled with two influxes, a “cold water” surface-derived source (“cold” here meaning “below boiling”, but not necessarily by much), and a much hotter deep source that serves as a source of both heat and water. If that’s the case, then the primary heat source is fairly point-like: one or a few very small fissures. Again for Old Faithful, the hottest temperatures are evidently at the bottom of the conduit (about 118° C, with short durations of 129.5° C observed). When you consider the rate of heat loss from the system, this makes some sense: it’s difficult given the thermal conductivity of rock to directly heat the conduit.

> It is interesting to think about.

I couldn’t agree more :).

Another person privately suggested a possible mechanism for the “two chamber stall” situation I was seeing (perhaps cool water from one vessel stalls the active chamber by quenching the steam as it rises). That’s a really good idea – too bad I don’t (yet) have the thermocouples to show it, or an all-glass branched conduit system (too expensive, given my lack of knowledge).

Again, thanks to all of you for tolerating my questions, and providing some fascinating food for thought.

-- 
Brian Davis