The road on the other side of the valley was closed by a mudslide. The mud was four feet deep across the road, and it took two days to get the road cleared.
This is where the mud entered the road.
A major irrigation ditch runs parallel to the road. It’s not filled with water yet, so mud filled the ditch and flowed in both directions. The road crew cut a hole in the ditch so the mud could flow down into the orchard and out of the road.
That red triangle of earth is a cross section of the far wall of the ditch–the near wall is under mud so you can’t see it. The road crew cut a notch in this hundred year old irrigation ditch so the mud could drain from the road and hopefully from the irrigation ditch as well. Below, a section of the rail fence was removed so the mud wouldn’t sweep it away. There is a lot of mud being held in by the solid fence on the left.
I realized the next day that I didn’t have a shot of the rockslide where this material originated. Today was overcast so the picture is a little bland, but you can see how the color of the mudslide matches the color of this high altitude rockslide.
This is technically a debris flow, not a mudslide–it’s not topsoil that’s moving, but subsoil. In the San Juan mountains, these debris flows are triggered by water; this one in particular is from last winter’s heavy snowpack and the quick meltdown. In some places, mudslides are a product of human interventions like deforestation, agriculture or road construction; here they’re a function of the region’s geology, and of water.
The debris flows start when the snowpack melts, and continue intermittently through the summer. A big rainstorm can move the mountains as well as the melting snow. In this area, water moves the earth.
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