After surfing at the WAVE CAVE, I decided since I drove all that way, I should make the most of my day. Today was a great day to visit BTA as they were having a geology tour at 1:30. The tour was being led by 3 different geologists of Resolution Trust Corporation. They lead this tour once a month. We start with a slide show in one of the meeting rooms where they discussed how this area was formed. They were also willing to take any questions regarding the copper development in the area.
They discussed the 3 kinds of plate movements and what the results of that were. What was most interesting about the presentation is that they emphasized that this area was effected by caldera eruptions, a gazillion times more powerful than volcanic eruptions
. There were 3 such eruptions closest to us, those being in the Yellowstone area:
According to the U.S. Geological Survey...
The three caldera-forming eruptions, respectively, were about 2,500, 280, and 1,000 times larger than the May 18, 1980 eruption of Mt. St. Helens in Washington State. Together, the three catastrophic eruptions expelled enough ash and lava to fill the Grand Canyon
This type of volcano is shaped more like an inverse volcano. An enormous magma chamber bulges up beneath the ground from the extremely high pressures of the trapped gases within. Ring-shaped cracks form outward from the magma chamber toward the surface and these act as relief valves for the magma to escape. Once the accumulated pressure has been sufficiently released through a serious of extremely powerful pyroclastic and plinian eruptions, the ground above the magma chamber subsides or caves in, leaving a large depression.
From the evidence that scientists have been able to gather about caldera eruptions in earth's past, all signs point to events so cataclysmic that they may have changed the course of the evolution of life on earth.
Anyway, that's just a brief synopsis of caldera explosions. The word that kept ringing in my ear was PYROclastic... it just sounds devastating
. After the classroom we headed up the High Trail so that they could show us what they were talking about. If you look at my photoset, that is where I will explain a little more of what I learned. The guide seemed fascinated that we as hikers are very curious about our hiking environment; especially in the western Superstitions.
Needless to say, the layers we see are results of different events that occurred at different times. It is incredible to witness millions of years by looking at just one section of rock that perhaps has smooth rock below, conglomerate in the middle and a rougher rock on top let alone some basalt suddenly appearing only in one area. There are also many faults to observe and with their guidance I was able to follow the faults in the rock. And of course, what is interesting is that the newest rock is on top which is opposite of Glacier Park where the plates shifted in a more horizontal direction causing the older earth to rise to the top. Therefore in Glacier, you are seeing some of the oldest rock in the world on top.
We finished off the tour in the dry creek bed where there is one rock outcropping that displays quite clearly the conglomerate rock and the fault. I have a photo. I highly encourage you to go out and enjoy the BTA and take this tour.
Last, I found the information at this link to be a very good explanation as to the forming of the Supes: http://www.gemland.net/webblog/?p=66. The commentary provides this comparison -
The Arboretum Rocks! -- geology walking tour -- April 28
1:30 p.m. in April; tours move to 8:00 a.m. May 26, June 23, July 28 and August 25
Once-a-month geology walks are a chance to see rocks and volcanic formations along our main trail on a guided tour that compresses almost two billion years of geologic history into just over one educational hour! Learn about Pinal schist, the volcanic origins of Picket Post Mountain and the Apache Leap tuff.
Mt St Helens crater is less than a mile wide vs
the volcanic calderas in the Superstitions that are 10 to 15 miles across!
Of course I finished my day off in the Demonstration Garden. You know it's a bad moisture year when it looks like even the BTA flower garden is struggling
. Nonetheless, there were many photo ops but surprisingly enough, I left before the BTA closed; something I usually never do. I also happened to run into Colleen Miniuk-Sperry, the trainer from the Photo Workshop I had attended a few weeks prior. She is the co-author/photographer of the recently published guidebook, "Wild in Arizona: Photographing Arizona's Wildflowers; A Guide to When, Where, and How". Her co-author Paul Gill was also there.
Needless to say, I had a full day. You just can't beat a nice short Supes hike with a walk around at BTA.