_To the Editor of the Scientific American:_
Some years ago I visited the "Ice Cave" of Decorah, Winneshiek county,
Iowa, and having since been unable to receive any explanation of the
wonderful phenomenon exhibited by it, I write, hoping that you or some
correspondent may explain the paradox.
The thriving town of Decorah lies in a romantic valley of the Upper
Iowa River, and the cave is almost within its corporate limits.
Following the left bank of the stream, one soon reaches the vicinity,
and with a hard scramble through a loose shale, up the side of a
precipitous hill, forming the immediate bank of the river, the
entrance is gained--an opening 5 feet wide and 8 feet high. These
dimensions generally describe the cave's section. From the entrance
the course is a steep decline--seldom less than 40°. At times the
ceiling is so low that progress on hands and knees is necessary. About
125 feet from the entrance the "Ice Chamber" is reached. At this spot
the cave widens into a well proportioned room, 8 by 12 feet. The floor
is solid ice of unknown thickness, and on the right hand wall of the
room a curtain of ice drops to the floor, from a crevice extending
horizontally in the rock at the height of one's eyes. Close
examination discovers the water oozing from this crevice, and as it
finds its way down the side it freezes in the low temperature of the
chamber. Singularly this one crevice, and that no wider than a knife
edge, furnishes this, nature's ice house, with the necessary water. It
was a hot day in August, the thermometer marking 80° in the shade
when the visit was made, and comparatively the cold was intense. In
common with all visitors, we detached some large pieces of ice and
with them hurriedly departed, glad to regain the warmth of the outside
world.
The most remarkable fact in connection with this wonder is that the
water only freezes in the summer. As the cold of actual winter comes
on the ice of the cave gradually melts, and when the river below is
frozen by the fierce cold of Northern Iowa, the ice has disappeared
and a muddy slush has taken the place of the frigid floor. I would add
that the ice chamber forms the terminus of the cave. Beyond a shallow
crevice in the crumbling rock forbids further advance. The rock
formation of this region is the Portland sandstone.
Why should the temperature of the ice chamber be such as to freeze the
water trickling into it? And above all, why should the ice disappear
with the cold of winter?
Mansfield, O. H. M. W.
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