Tuesday Geology Picture: A Gneiss Double Arch Bridge in Valle Verzasca

An old stone bridge spanning the Verzasca River, Lavertezzo, Italy, June 2010.

Since I’m too busy for regular blogging, this week is geology picture-a-day week here at Georneys. Several other geobloggers have also decided to join me in this blogging meme. Feel free to start today, even if you didn’t post a picture yesterday.

Today’s geology picture is of a beautiful, old double arch bridge spanning the Verzasca River at Ponte dei Salti in Lavertezzo, Switzerland. The middle part of the bridge rests on a small section of uplifted gneiss. The Verzasca is a fast-moving mountain stream that has carved a narrow, V-shaped valley in the crystalline bedrock, which is gneiss of both sedimentary and igneous origin. The river is renowned for its bright color (turquoise in places), beautiful rocks (the gneiss ranges from light brown to gray, with the colors intermingling), and deep pools. The pools are so deep that they are often frequented by divers.

I visited the Verzasca River back in 2010 as part of a class field trip for the Geodynamics Course at Woods Hole Oceanographic Institution.

Water: Morganza Spillway Opened for First Time Since 1973

Saturday afternoon the U.S. Army Corps of Engineers opened part of the Morganza spillway— a flood control structure in Louisiana along the Mississippi River– for the first time since 1973 (and for the just the second time since the spillway was constructed in the 1950s). The spillway was opened yesterday to help mitigate severe flooding in the Mississippi River system. Just one floodgate was opened. As needed, additional floodgates of the spillway will be opened. The opening of the spillway diverts floodwaters from the cities of Baton Rogue and New Orleans. Hopefully, the opening of the spillway will spare those two cities from severe flooding. However, the opening of the spillway means that much of low-lying, rural, south-central Louisiana will be flooded. Large parts of Louisiana have already been evacuated. The floodgates will need to remain open for weeks until the river levels drop.

The impact of the flooding on Louisiana is going to be extensive: crops drowned, homes destroyed, people displaced, communities thoroughly soaked. I imagine many communities will take years to dry out, rebuild, and recover, even if the floodwaters recede in a few weeks time.

I suppose Louisiana had no choice but to open the floodgate. The rain just kept falling. The U.S. Army Corps of Engineers can only work to minimize the damage caused by the flooding by strategically diverting the water to less-populated areas. The flooding along the Mississippi is a potent reminder for all of us of the immense power of rivers and of the hazards of living close to and trying to control a large river.

Here is an impressive video showing the opening of the single floodgate today:

Video taken from YouTube.