Geysers as eroders show that the under earth is hot and is invaded by rainwater. In exceptional volcanic places the water is boiling hot. The Firehole River of the Yellowstone is carving down basins of solution faster than the regular geysers are building up siliceous sinter. Here is boiling-spring erosion by solution. It may be called the extreme thermal aspect of ordinary spring-water erosion. How does spring water erode? By bubbling up under the beds of rivers. The bubbling out of springs starts rivers, and flood rainfall starts soil gullies; land sculpture is the result.
We introduce geyser experiments here because boiling springs make drama out of ordinary springs, just as active volcanoes make drama out of buried volcanoes. Ordinary springs and buried lavas intruding invisibly are much more important and extensive than geysers and volcanoes. Most people never think of a spring as one of millions bubbling up the beds of brooks and rivers and sea bottoms.
Most people never think of volcanoes erupting—properly speaking, irrupting or inrupting—under Kansas or Brazil. Nobody denies those places are hot underground, but it all seems remote. Yet every spring is thermal if there is heat escaping through the rocks around it.
Geyser basins lower the country around them and leave hills in relief. The proportions of basins and hills depend upon the runoff of rotting and dissolving rock. The shape of a hill standing high, what Davis called a monadnock in New England, depends on its whole history, not on its hardness. Ascutney Mountain stands high as a lump because surrounding slates have rotted down. Mount Monadnock may stand high because the springs under the river pattern of cracks neglected it in the rotting and crunching of a continent.
Dynamic weight eternally falling makes low places. Hardness against weathering makes a mountain high only as a relic or residual. It is a node in the gigantic process of gravitation rotting and the spring squirting of groundwater. The water heats, rises, dissolves, siphons, springs up, and transports dirt. Underneath is a definitely heated earth crust.
Accordance of summit levels of mountains and hills as one looks across country does not have to represent an upraised plane surface. There is more undermining where the spring squirting is most voluminous. When spring squirting is equal, the opposed slopes of a valley adjust themselves. The tree line, the snow line, the rain line, and the wind line are definite levels of erosion. Under it all the rotting rock is falling toward the earth’s center, slowly, creakingly. The everlasting hills are not everlasting, they are everfalling; rocks, boulders, slopes, waters, gravels, sands, and muds. And adjustment to the atmosphere and groundwater surface is irresistible.
1. Experimental Geology Laboratory, Harvard University, 1900
2. Fountain at edge of lava lake, May 17, 1917