Sunday, August 24, 2014

Kilometer-long crack opens in Hermosillo - an earth fissure?

A kilometer-long fissure opened up along Mexican Highway 4 between Hermosillo and the Gulf of California coast recently.   Hermosillo Desde el Cielo flew a drone along the fissure capturing excellent video of the  8-m deep feature.

The local newspaper is reporting that farmers had built levees to collect rainwater.  Such features show up in the drone video, striking perpendicular to the fissure.

AZGS geologists who reviewed the video and reports say it looks like earth fissures found in Arizona and other areas subject to rapid groundwater withdrawal and subsidence.

In Arizona we've seen fissures open up in hours during heavy monsoon rains, as the water enters small cracks that extend down hundreds of feet in depth.  The water rapidly erodes the soft basin sediments, carrying them for hundreds or thousands of feet laterally.

The pooling of rainwater on the ground over an incipient fissure could provide the volumes of water comparable to that of a big rain storm, and cause similar erosion.   So, in this scenario, the fissure does not so much open by extension as the sides are quickly washed away into the long deep narrow incipient crack.   However, it's unprecedented to see one this big form so quickly.

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