El Calderon at El Malpais

On our trip (of which only 1/3 of participants was a geologist) we were able to make a quick stop at the El Malpais National Monument. This area is renown for it’s rich volcanic terrain and as a studying geologist that’s interested in volcanology and potentially will be visiting the area again this Fall in an expanded capacity, I was really excited to check some stuff out. Our time was limited, so after stopping by the visitor center we decided on a short little hike that would let us see some lava tubes and a volcano.

The area we decided upon, at the ranger we spoke too’s suggestion, was El Calderon. El Calderon is a cinder cone volcano that was formed around 115,000 years ago from lava fountain style eruptions. Sometime after the fountaining stopped, the eruptions continued in the form of fast moving basalt flows that carpet a wide area in the vicinity today. This period of basalt flows leaves a jagged terrain of vesiculated rocks, but more interestingly to me, a geology enthusiast from the flatlands of Illinois, it left behind the tubes by which that lava flowed all those years ago.

You can see on the poster above (maybe) that these tubes are now closed off to the public to protect the bat poulations from the threat of White nose syndrome.  Fortunately for us, there are smaller, partially collapsed lava tubes available to traverse on the El Calderon trail, and traverse it we did.

It’s really dark inside the tubes, so these were the only images I was able to grab, but it was a really cool experience. I wish we had the time and permission to go further into them. The lava tubes, when they’re open to the public, are pitch black, trail-less caves to explore.

This is a sample of what all the rock in the above images is like… It’s very sharp, jagged, highly vesiculated basalt. It’s not kind on the body when you miss a step and trip or need to catch yourself when slipping.

Vesiculation (formation of gas bubbles; and thus the holes in the above image) occurs under several conditions; increase in temperature of the lava, for example when there is an influx of newer, hotter magma; increase in the concentration of volitailes (CO2, SO2, etc.) usually by the crystallization of anhydrous (water-phobic)  minerals; or a decrease in pressure  caused by the ascent of the magma/lava. In the case of El Calderon, the lava flows were apparently very fast and moved long distances quickly so I think it’s  case of the latter, where the lava quickly made it’s way to the surface and became highly vesiculated in the process. I also could be way off, I have almost zero background information beyond a few brief web pages.

After we exited the lava tubes, we made our way to El Calderon itself with every intent to get to the crater. Teejay is doing some sort of crip-walk or something here apparently.

Unfortunately, shortly before reaching the base of the volcano, there was a fence, a gate and a Private Property sign. That seemed odd, so we think we took a wrong turn somewhere, and in the interest of time, we had to turn around and head back to our car.

The whole experience made me really excited to head back there sometime though. I would love to spend some time in the field there and observe many of the phenomenon that I’ve only read about and seen in picture.

ALSO: Nearby is the Bandera Volcano and Ice Caverns and their website said they opened at 8am, so we showed up at 8am. When we got there the sign said they opened at 9am. FUCK EM. We went here instead after that (The other place still sounds super awesome though, so fuck em in the sense like “Damn! I really wanted to go!” not “Fuck those shitty assholes.”).


Castle Rock

Last weekend, I hopped on my bike and made the 30 mile round trip trek (personal record for me :D) to nearby Castle Rock in order to spend some summer somewhat within my educational pursuits. Castle Rock is an exposed piece of the St. Peter Sandstone, a very mature, very pure quartz arenite formation that most geologist and students of the Midwest are likely familiar with, located between Dixon, IL and Oregon, IL on Illinois Route 2 in what is now known as Castle Rock State Park.

The St. Peter Sandstone is a Middle Ordovician formation dated between 465 and 460 million years ago, that is widespread throughout the Midwest. It’s deposition coincides with the beginning of the Tippecanoe Sequence (A Sloss sequence or cratonic sequence; a sequence that describes the transgression and regression of sea levels, and consequently deposition and erosion across a craton), a period of relatively higher sea levels covering the craton in a shallow sea; a perfect environment for the deposition of the sand that would become the St. Peter Sandstone.

The distribution of the St. Peter Sandstone formation (I live a bit north of Ottawa); taken from Mostly Maps (http://mostlymaps.wordpress.com/2009/12/20/sands-of-time/)

Approaching the park, your first glimpse of the St. Peter Sandstone is the rock exposed by the road cuts that follow Route 2 as it twists through the bluffs that line the Rock River. Unfortunately, rather terrifyingly, and much to my dismay as I had apparently forgotten, the well-traveled Route 2 loses it’s shoulder here, and the blind curves make a cyclist a rather large roadside hazard. I am happy to report that I survived, however.

There are few things of note in the next photo (I also apologize for the quality, I feel like there was something wrong with my settings this day); first, the obvious cross-bedding or more accurately cross-lamination, and secondly how loosely cemented the rock is. It’s very friable (a good word for geology students to know), meaning it very easily crumbles at the touch. It’s not very well cemented together.

The cross-lamination provides an insight into the history of the deposit; you can determine the direction of flow that deposited the sands, and you can rule out certain depositional environments based on the angles of the laminations. For instance, the cross-laminations observed at Castle Rock are very low angle; these are associated with deposition by water as opposed to deposition in the dunes of a desert, where cross-bedding is much more prominent and much higher angle.

A short way down the road from the road cuts is the Castle Rock area itself. A set of trails and some river side recreational areas. The really unfortunate thing about Castle Rock now is that the Illinois DNR  has covered it with a bunch of wooden walk ways and makes it really less than ideal for people interested in the rocks to examine them. Sample taking and climbing on the rocks is strictly prohibited in the interest of preserving the site.

It’s still possible to see some of the features of the formation however, note the lamina and bedding, and more cross-lamination’s visible here.

Below the Castle Rock, along the river there are plenty of exposures too, but most of them are inaccessible unless you have a boat, but there are some along the shores that you can approach and that have some interesting features.

In the lower right of this next photo, you can see a dark layer in between the sandstone, something that hasn’t weathered at the same rate as the surrounding rock. I have no idea what it is, and it’s so localized that it’s hard to find any other spots with the layering present and again, it’s very illegal to take samples from the area so if you have any ideas, shoot them my way. The area is clear of brush though, as if someone has spotted it before and has also examined it.

If you follow the shore south, you come across a nice face you can look at, but like I said, most of this stuff is only accessible by boat. The river is a little low right now, so I was able to get this by compromising with muddy shoes.

…and here is a nice shot of the scenic view from atop Castle Rock. It’s really a nice place to check out. It’s not a geology mecca by any means, but it’s local and a nice place to have a picnic.