312 ANNUAL. REPORT SMITHSONIAN INSTITUTION, 192 8 



Tree molds exist in certain flows in the Craters of the Moon 

 where the lava flowed slowly and at the right temperature into a 

 forest. The molds vary in diameter from a few inches to 3 feet, 

 and are easily distinguished from other holes in the lava. Many of 

 them are 10 to 20 feet in depth. Molten lava does not completely 

 destroy a tree because a few inches of solid lava crust prevents any 

 great amount of heat from escaping through it, and liquid lava at 

 or near the cooling point requires very little time to solidify into a 

 poor heat-conducting shell around the tree. While the tree is burn- 

 ing it shrinks away from the surrounding lava, creating an air 

 space or chamber between the tree and the mold which accelerates 

 the cooling. The process is further aided by the steam from the 

 sap of the tree. There is much less chance of the formation of a 

 mold from a dead tree, for it burns too rapidly. The writer saw in 

 Hawaii two years after the eruption trees only partly buried by 

 lava with their upper portions uncharred and dead leaves clinging 

 to the branches. 



Most of the vertical tree molds do not preserve any charcoal im- 

 pressions, but where the tops of the trees fell on plastic lava the 

 mold of the charred log and the grain of the wood is sometimes 

 preserved. In places the lava was soft enough or rendered sufficiently 

 plastic by the steam from the burning wood to flow into the shrink- 

 age cracks in the charred surface of the log, forming a checker 

 pattern easily mistaken for bark impressions. No tree mold showing 

 bark impressions was found in the monument. 



One kind of tree mold, called lava trees, is common on Trench 

 Mortar Flat southeast of Big Cinder Butte. These trees rise 1 to 

 5 feet above the lava surface and were formed in the same manner 

 as the tree molds, except they were in places from which part of the 

 lava flow could drain away, or else they were buried by spatter from 

 a spatter vent. 



Ice-cold water is found even on hot July days in the most unex- 

 pected places, its temperature rarely exceeding 2° F. above freez- 

 ing. Most of the large water holes occur in depressions in very 

 rough broken lava, where much snow collects in the winter. Some 

 of it sifts down into the crevices between the rocks and remains 

 sheltered during the summer days. Water during the thaws may 

 drip downward into the crevices where it is frozen by cold circulat- 

 ing air. Some melts in the summer, but in favored positions it 

 never entirely melts away, as the lava is a poor conductor of heat. 

 If one digs down into the loose rock in a water hole of this type 

 ice will always be found beneath the water. 



Water and ice occur also in the lava caves or tubes where draughts 

 of cold air freeze any water that percolates into them. This occurs 

 about seven months in the year, and during the remaining month? 



