[Geysers] Eruption Height

[Michael Goldberg]

As it turns out, most of us have untrained eyes.

The _Sput_ has an article circa 1989 describing an experiment in 
which three geyser gazers measured (with instruments) the height of an 
eruption of Grand from three different vantage points.  Their results 
disagreed wildly.  That discouraged everyone from trying to measure Grand 
for a while.  When the old boardwalks were removed, the surveyed 
benchmarks at Grand and other geysers came with them.

There is a tradition as old as the Park itself of guidebooks repeating the 
same geyser descriptions and height estimates without question*.  Grand 
Geyser is believed to erupt as high as 200 feet because the Hayden survey 
estimated so back in 1871.  Well, that and the fact that it's still a 
plausibly optimistic figure...

There is only one reliable method I know of to make off-the-cuff height 
estimates, which is to know in advance the apparent eruption height 
corresponding to a fixed benchmark.  The old visitor center used to 
measure Old Faithful relative to a tree in the foreground**.  This worked 
because the viewing location was very well standardized.  Similarly, the 
horizon behind Steamboat/New Crater Geyser corresponds to an eruption 
height of ~25 feet.  There's no reason we couldn't do the same for Grand.
Caveat: since the eruptions are not precisely vertical, it would be best 
to do this from a distant vantage point.

Completely unreliable methods include: comparing to a geyser of known 
height (i.e. Grand was twice as tall as Riverside) and gauging how long 
water droplets hang in the air before returning to earth.

Collectively, I think gazers have are OK at comparing two eruptions of the 
same geyser.  We're much worse at deciding if Beehive is typically taller 
than Grand and Old Faithful, or some other way around.  And we are 
terrible at assigning actual numbers, in part because so few careful 
measurements have been taken in recent memory.

For what it's worth, my personal strategy for most geysers over 30 feet is 
to take the height that I "would like" the eruption to be, then subtract 
20 percent.

Here's how this works in practice:  Let's suppose I am watching Castle 
erupt, and it has a rather nice episode of jetting.  I could stretch to 
convince myself that it was 75 feet tall.  But with Castle I can also 
perform a reality check, using the 12-foot cone as a measuring stick.
Chances are the objective result would come up 20% lower, near 60 feet.

You tell me -- which number sounds better, 60 or 75?

Michael Goldberg
mikeg at math.jhu.edu

* It's not just geyser gazers.  According to Richard Feynman's memoirs, it 
took scientists years to correctly determine the charge of the electron, 
because of a collective deference to Sir Robert Millikin's original 
measurements.  Which were a bit off.

** If someone could create a measurement scale for Old Faithful eruptions 
on the webcam, I'd really appreciate their efforts, and I'd love to know 
the eruption height in the attached screenshot.


On Mon, 18 Jun 2007, John Taliaferro wrote:

> Thanks to those gazers who put up with my lame questions during my 
> initiation into earnest gazing on 14-15 June. Everybody has firsts, and 
> mine were marvelous: Grand (twice), Daisy, Castle, Riverside, and Lion, 
> to name the high points. Among the many things my untrained eye had 
> trouble evaluating was the height of any given eruption. For instance, I 
> guestimated Grand's bursts at roughly 100 feet. I was informed that they 
> were at least 150, perhaps 180 feet high. Question: Is there a 
> recognized technique for measuring eruption height without relying on 
> actual instrumentation? How do you guys do it -- or is it best not to 
> try? Thanks. John Taliaferro
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