Blowhole Cave Geology Trip

Reprinted from The Utah Caver Volume 10, Number 5, October 1998

Blowhole Cave, Utah, Trip Report

With Supplemental Data on the Mineralogy and Elemental Composition of Sediments

By Fred Luiszer, University of Colorado

On Trip: Fred Luiszer, AI Hinman, David Herron, Dale Green Trip Date: March, 1998

Over the years many cavers have told me of the banded red, black, and, white sediments, known as the Navajo Blanket, at Blowhole Cave. I was intrigued at the possibility that they may have an origin similar to the sediments that I have studied at Cave of the Winds in Colorado. With this in mind I decided to visit the cave and study the sediments. At their invitation, I had the pleasure of accompanying Dale Green , Dave Herron and AI Hinman to Blowhole Cave in March of 1998.

I left Boulder, Colorado on Friday morning arriving at Al's house near Mountain View, Wyoming that afternoon. That night it snowed, but we figured that it had to be better in Salt Lake City, which is near the cave. As we drove toward Salt Lake City on Saturday morning the weather deteriorated. By the time we got to Dale's place it looked even worse, but Dale, being an optimist, assured us that it was only bad there because of the dreaded Lake Effect. And, of course, being equally optimistic, we believed him. As we traveled south from Salt Lake to meet Dave the sky grew ominous and it began to rain. By the time we met Dave it was snowing fairly heavily. Dave had decided to park his truck on the paved road, because his truck was only two-wheel drive and the dirt road to the cave was already looking bad. As he started to turn around his right front tire just barely left the road and instantly sank into mud. Luckily we had two 4X4 with us, so pulling him out was no problem. At this point any sane person would have looked at the falling snow and horrible road conditions, and would have called off the trip. Being cavers we just shrugged and said, "What the heck we came this far, lets give it a go". After a few miles we came to the secret turn off that bypassed the hundred-foot-wide mud wallow that in dry times would have passed as a road. After driving a few hundred yards on the bypass we came upon a 4X4 that had slid off the track and became tangled in a barbed wire fence. At this point any sane person would have called off the trip. But, Nooooo, we were cavers, nothing was going to stop us. AI produced the implements of destruction and the 4X4 was soon free. By this time the road had turned into a substance not unlike unctuous snot. It was only by the excellent driving abilities of AI and Dale along with a large dose of foolhardiness that we finally arrived at the cave.

As we tied off to AI's truck and prepared to repel into the cave the sky seemed to clear a bit. We were using my rope, which had not been used for several years, so I volunteered to go down first. I had been warned that the cave was warm (70 degree F), but was unprepared for the instant fogging of my glasses, which I quickly removed. My considerate companions then warned me that snakes, especially rattlesnakes, were common inhabitants of cave entrances in these parts. For a moment I thought to myself, here I am under a threatening sky, repelling virtually blind down a rope of dubious pedigree into a cave I have never been in that may be replete with poisonous snakes. But I figured, hey I had just lived through AI's driving on the Road to Hell. This situation couldn't be that much worse.

As I dropped down a little deeper into the pit and neared the first semi-flat area I spotted a small snake. Of course without my glasses I was only a few feet from it before I saw it. Fortunately, my companions assured me that it was a non-venomous snake. We all make our way down to the Navajo Blanket, where I took several samples of the finely bedded red, black and white sediments. I had specifically come to look at and sample these sediments because of their similarity to the sediment that I had studied at Cave of the Winds in Colorado. Dave also took a sample of what appeared to be bedrock corrosion residue that he wanted me to analyze.

The sediments at Blowhole Cave are very similar to those at Cave of the Winds (Table 1). Both caves have layers of Fe- and Mn-oxides associated with calcite. Additionally the Fe- and Mn-oxides at both caves contain elevated amounts of As, Pb, Sb, Zn, Ni, and Ba (Table 1). It should be noted that out of the dozen different caves in the West where I have analyzed sediments of this type, the sediments at Blowhole Cave have the highest arsenic value. Studies at the University of Colorado have shown that these arsenic and lead rich sediments have a low bioaccessibility, that is to say that a caver would have to eat quite a bit of this sediment before they would have to worry about any ill effects. The similarity of the sediments at Blowhole Cave and Cave of the Winds (Table 1) suggests that both caves have had a similar genesis. At some time in the past, springs existed above both of these caves. The caves were conduits that channeled water from two sources, a deep-seated, mineral-rich water and a near-surface oxygen rich water. As these two waters mixed in the cave a solution was created that dissolved limestone and precipitated Fe- and Mn-oxides. For a more detailed discussion of this process see http://spot.Colorado.EDU/-Iuiszer/ where you can download my entire dissertation and bore-yourself silly.

The bedrock corrosion residue sample that Dave collected was fairly pure calcite with only traces of other elements. It appears to have a mineral composition and morphology that would be more similar to moonmilk. To say the least, much more scientific studies need to be done at Blowhole Cave.

Another feature of the cave that should be looked at is the blowing air. I have been told by Utah cavers that Blowhole Cave always blows warm air (-70 degree F) out of the cave. I would assume that this is the result of chimney effect from cooler air entering a lower entrance. The enigma is the source of heat. Apparently early explorers of the cave believed that there was a hot spring just below the surface. To this end extensive digging was undertaken to reach the hot spring. I was told that the steel cable in the cave was used to haul debris out of the dig. Knowing only a little about the local geology and hydrology I would assume that the local water table in the limestone, which hosts the caves in the area, is probably a few tens of feet above Utah Lake. This would give Blowhole Cave the possibility of having over a thousand feet of vertical development. If there was a lower entrance near lake level, the warm blowing air could be explained by the geothermal gradient. This model, however, has a major problem. A normal gradient would only account for a few degrees increase in temperature at the maximum estimated depth of Blowhole Cave. This would suggest that there is an anomalously high geothermal gradient or that indeed there is a hot spring in Blowhole Cave at depth.

Years ago I had an idea to find lower entrances to chimney effect caves by reversing the air flow on a very clear, cold winter day by attaching a very powerful fan (like the gas powered fans that they use to blow up hot air balloons) to the entrance. I wonder how much it would cost to rent one of them for a day? Oh well, so much for science and theories.

After collecting the samples we began our exit from the cave. As we ascended the rope we noticed a very small trickle of water coming into the cave. As Dave and Dale ascended the trickle of water increased in volume. The water volume increased even more as I climbed out. The reason for the increasing water flow became obvious as I climbed out of the cave into a snowstorm. I yelled down to AI that he might think about getting out of the cave as quickly as possible so we could get of the hill and onto pavement while the getting was good. As AI was ascending the rope, two 4X4 trucks stopped not that far from the cave. They asked a very simple question, "Where are we?" Jeez... and I thought we were nuts.

We piled our gear into the vehicles as fast as possible and quickly made our way down the hill. In a matter of minutes we had caught up to our lost fourwheeling folks who had managed to stall one of their trucks. The trip back to the paved road was not quite as exciting as the ride in, mainly because I was getting used to AI's driving. After parting ways with Dave and Dale, AI and I drove back to his place through one of the worst snowstorms I had ever seen, but that's another story.

Elemental Composition of Cave Sediments

Blowhole Cave	Ti*	Mn%	Fe%	Ni	Zn	Sr	Y	Zr	As	Pb	Sb	Ba
Mn-Fe oxide mix, dark brown	16124	14.14	38.28	1100	3600	422	343	259	23259	331	99	19700
-95% iron oxide, red	2913	0.22	56.57	105	409	50	68	53	11836	173	287	138
-100% iron oxide, red						52	118	74	20929	621	1800	458
Calcite?, white	91	0.01	0.37	285	27	120	1	0	27	0	2	30
Calcite? wall snot, gray	63	0.01	0.39	277	2	154	1	0	46	15	2	0
-100% iron oxide, red				208	670	39	52	67	21729	446	1100	297
Cave of the Winds
Hollandite (19 cm depth)		39.01	0.80	294	1500	2300			39	22	32	63500
Goe+Hem (39 cm depth)		1 .50	73.23	197	1472	120			8800	6200	499	777

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