Like the ProjectThe following is a transcript of the narration for this panorama location. To watch and listen to the narrated panorama, enter the project here at this location and then press the play button.
To get to this spot you have to take a small detour off from the Thunder River Trail, but you are rewarded with a tremendous view of Surprise Valley, spreading out beneath you to your south, with Cogswell Butte just beyond, and, the huge mass of Great Thumb Mesa forming the South Rim, on the far side of the Colorado River.
Behind us, to the northwest, are the massive walls of Redwall Limestone and the Manakacha Formation within the Supai Group that block descent from the Esplanade to Surprise Valley. But we have, nonetheless, been able to hike down to this spot, below the base of the Redwall. But if we look down at our feet, we can see that we are standing on Redwall Limestone, which was once was part of that cliff.
Our tremendous view from here is provided by a gigantic block of Redwall Limestone that has torn away from the cliff face. And this block is in fact just one of a row of three gigantic blocks. The second block is nearby to the east, and you can see just a bit of the third block peeking out to the right of the second. Notice the extreme tilt of the formation within the block, back towards the cliff face. All three of the blocks are tilted in the same way, back towards the cliff face face behind them. If we head back up the trail for a moment, to the top of the actual Redwall cliff and look back down towards here, you can see all three of the blocks rising up in a row from the floor of Surprise Valley, all with the same back tilt.
Coming back to our current panorama spot, but then looking back to where we just came from at the top of the Redwall Limestone, we can trace our path down to here following the Thunder River Trail. But there is no Redwall Cliff to be seen. The trail meanders through a maze of rubble, including huge blocks of orange colored Esplanade Sandstone that have tumbled down from much higher up.
What we are looking at, and are standing directly on top of, is the famous Surprise Valley Landslide. Landslides are common in the Grand Canyon, but this one is about as big as they get. Huge blocks of stone, estimated to total a cubic mile in volume, came crashing down from a four mile long stretch of cliff face, perhaps in a single cataclysmic event, sometime within the last million years. In some places giant blocks dropped 2000 vertical feet.
If we look back towards the northwest, where we looked before at the intact cliff faces, but now if we look down lower, notice the bands of rock below the cliffs that are a bit slanted. If you are familiar with the color and texture of Grand Canyon rock formations, you would think that you are looking at the usual progression of formations within the Supai Group. And you are in fact looking at just that, but they are in the wrong place, shifted down hundreds of feet, and tilted a bit, sliding down in a huge mass within the landslide. And the Redwall Limestone, even harder than the members of the Supai Group, tore away and mostly held together in gigantic blocks, including the one we are standing on.
What could cause such a cataclysmic event? You might want to blame an earthquake, and though an earthquake may possibly have been the immediate trigger, but the root cause is a fundamental instability in the rock formations. This chart displays the normal stack of formations in the area. The Supai Group, Redwall Limestone, and Muav Limestone are all hard, resistant, cliff forming rock formations. Below them is the Bright Angel Shale, which is a much softer, easily erodible rock, which is responsible for forming the Tonto Platform elsewhere within the park. The floor of Surprise Valley is Bright Angel Shale, and as Bright Angel Shale, throughout the Grand Canyon, erodes away much more quickly than the cliff forming formations above it, it undercuts and destabilizes the higher formations, which eventually will come crashing down, though not usually in such a spectacular manner as we see here.
When a huge ‘mega-landslide’ takes place, such as we see here, something triggers a massive, cascading failure within the Bright Angel Shale, and, as we see in this chart, showing the formations after the slide, the entire set of harder, rigid formations above the Bright Angel Shale comes sliding down as one giant mass. Since the top surface of the Bright Angel Shale is curving, concave surface, the entire sliding mass gets tilted back, towards the remaining cliff face, exactly as we witness here in the dramatic tilt of the Redwall Limestone blocks. Geologists call tilting blocks like this torevas, and you can find torevas, each the result of a massive landslide, scattered throughout the Grand Canyon.
One theory of the origin of the Surprise Valley and other megaslides is water. If a lot of water is present, it can saturate and weaken the Bright Angel Shale, causing it to give way. One of the largest springs in the entire Grand Canyon, Thunder Spring, is just east of here, and its presence may have triggered the slide. But there may have been another source of even more destabilizing water, and we’re heading downstream on the Colorado River for 45 miles to have a look at it. On many occasions over geological time huge landslides and lava flows have dammed the Colorado River, forming a huge reservoir upstream for a brief period of geological time until, inevitably, the river breaches the dam and returns to its usual state. Here, from the Toroweap Lookout, we can see Lava Falls, a giant lava flow from relatively recent geological time. The river today has cut through the bottom of the lava flow, but when it first formed it dammed the Colorado and created a lake something like this, and that lake would have been deep and high enough to flood Surprise Valley, 45 miles upstream, reducing the strength of the inundated Bright Angel Shale past a critical point, causing it to give way in a huge, cascading failure throughout Surprise Valley, and miles of massive walls may have all come tumbling down in one spectacular event.
When you are ready to move on, scamper back down the spine of the ridge behind the Redwall block back to the Thunder River Trail, where we’ll head up to a spot that should be right in the middle of the Redwall cliffs, but where we are instead surrounded by the debris of the landslide, including massive, house size blocks of Esplanade Sandstone from far above.
If after scampering back to the Thunder River Trail we head down the trail instead, we will wind our way down and around just to the west of the Redwall block, and then quickly reach a split, where you can either head left and continue down Thunder River Trail, though Surprise Valley, over to a panorama spot near the eastern rim of Surprise Valley, in the midst of another giant landslide.
Or you can turn right at the junction and start down the Deer Creek Trail and eventually reach the Colorado River at spectacular Deer Creek Falls, but stopping first at a panorama spot in the heart of Surprise Valley, at a fine spot to stop and enjoy another view of the spectacular Surprise Valley Landslide.
