Life on Lava
The beauty of today’s Columbia River Gorge is the result of cataclysmic geological events. 40 million years ago the Columbia River passed through a wide valley that is today occupied by Mt. Hood volcano. Violent volcanic eruptions with streams of lava, ash fall and mudflows of long since eroded volcanoes took place during the next 20 million years. Culminating in the fiery floods of lava between 17 and 12 million years ago the river was repeatedly deviated. When thick lava flows slowly cool, fractures form that propagate inward into the cooling lava body, because solid, crystallized basalt is denser and hence occupies a smaller volume than the melt. Such flood basalts often show a tripartite subdivision cross-section with thick hexagonal columns at the basement, thinner columns in the central zone and more irregular columns at the top of the flow. This pattern resembles the temperature zones within the cooling lava, being uniformly hottest at the basement and variably cooler on top. Today, these basalt columns are covered by mosses and ferns as abundant rainfall allows life on otherwise barren lava.
August 2008
Canon 20D, Canon EF-S 10-22mm, f/16, 4 sec, ISO 100, tripod