During their Orientation Week, they camped at the South Rim for four nights. I led them on a hike down the South Kaibab Trail to introduce them to some aspects of the geology of the canyon. On Thursday, August 23, storm clouds began to develop as they listened to a talk at Hopi Point. A few claps of thunder could be heard away in the distance. Then, one was heard that just kept rumbling and rumbling and never stopped. The students quickly looked into the canyon and saw a large billow of red dust and rock floating up from the south side of Shiva Temple. A rockfall was underway! This image was captured by NPS ranger Jacob Fillion.
The rockfall appears to have initiated in the upper portions of the Redwall Limestone, deposited during the Mississippian time period about 340 Ma (million years ago). Although the amount of material likely let loose in this fall would dwarf anything human, it is quite small compared to the overall dimensions of the canyon. Notice that evidence for other recent rockfalls is absent in this view and in most views of the Grand Canyon. It is likely that the canyon is not currently experiencing active widening or deepening in modern times and that it may undergo periods where it just sits there with nothing much happening. It is similar in many ways to the biological concept of punctuated equilibrium, whereby species undergo long periods of stasis interspersed with shorter periods of rapid change. Grand Canyon may also undergo a sort of punctuated equilibrium with regard to its formation. The agents that produce the punctuations in this case would be climate change, runoff amount in the river and uplift of the rocks. These are what initiate canyon cutting and widening.
In any event, the fact that our students got to experience a brief moment of canyon widening bodes well for their semester here in northern Arizona. We wish them well on their journey of discovery!
|Photo courtesy of Jacob Fillion, NPS|