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USGS Geology in the Parks

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Lava flow trail stop 10

After the Lava Cools

A clean slate

Whatever plant life existed before the Sunset Crater's fiery birth was completely obliterated by lava flows. Volcanic eruptions provide a clean slate, forcing life to essentially start from scratch. Very few of the necessities of life are found on freshly-cooled lava.

Trees preferentially colonize north-facing slopes
Shrubs and trees, like these Ponderosa pines, preferentially colonize north-facing slopes.

Water is critical

The nature of the lava and cinders poses considerable obstacles to recolonization by living things. You've already seen the bubbly, vesicular texture of basalt up close. When water falls on Sunset Crater's cindery surface, it quickly drains through, leaving little behind to support plant or animal life.

Here in northern Arizona precipitation as rain and snow averages just 16 inches each year. Plants have the best chance of establishing themselves on north-facing slopes where the shadows slow evaporation.

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