Secret Tunnels

This is the entrance to the ice caves north of Rexburg; they're basaltic lava flow tubes. As lava flows, the outer layer exposed to air cools more rapidly than the molten material in the flow's interior. A basaltic rind forms, successive flows add layers to the flow tube walls, and the lava in the tube shallows as the flow decreases to a stop. This flow tube has since been percolated by water which, in Idaho's climate, turns to ice. Most of the cave floor is covered in thick ice layers. The combination of ice and basalt flow textures offered a double-helping of fascinating geology. The ice formed stalactites, stalagmites, and dendritic "feathery" snowflake-like crystals. There were also some neat flow layers and fractures in the ice. Here's a shot of ice crystals covering the ceiling:
Beautiful basaltic textures:
Me and the roomies (Kyle, Parley, me, Tom, and Trevik). At this point, the tube was segmented into an upper and lower passage; as the flow level in the tube dropped, the surface cooled and formed a shelf across the larger tube. That shelf is where we're perched for the photo.
Here's a shot of the ice-covered floor. Half the time, we were on our backs sliding along, pushing with our hands or feet. I came away from this cave with some bruised knees and elbows and a few scrapes on my fingers -totally worth it.
THE "END"

Over the Thanksgiving Break

I travelled with a friend back to Arizona for the Break. She was nice enough to stop for her rock-geek passenger to see some ash fall and tuff units. This road cut is on the stretch of Highway 20 that connects I-15 with Highway 89, just southwest of Beaver, Utah. The geological map I looked at labeled volcanics of the region as Bullion Canyon volcanics. The lighter-colored units are ash deposits and the massive darker units are rhyolitic tuff.

The ash units contain concretions.


A real treat on the way back north was the slight detour to see horseshoe bend just outside of Page, Arizona. It's a very photogenic meander in the Colorado River. We got there just as light was fading after the sun had set. No, this picture isn't mine. But the one below it is. The meander is so deep that it's difficult to get the whole thing into one shot. I may try to piece my photos into a panorama.

Igneous Rock Exam

The pictures are cruddy. Fluorescent lighting will do it almost every time.
Last week's Igneous Rock ID exam went well. I went into the exam feeling pretty comfortable, and left it feeling like I had done well.
Today, I got my ID portion of the exam back; 98%.
I once again give credit to David Morris for a job well-done. What would school be like without that firm groundwork of understanding from David?I shudder to think.

Some of the samples from the exam

Extrusive Igneous Exploration

"Please try to remember how you would've felt about this stuff when you were seven or eight."
-David Morris

Here are a few shots from the "Lava River Cave" located 13 miles North of Flagstaff.
There are plenty of lava tubes to explore here in Idaho. It's on my "to do" list.
Humans present for scale
Flow texture of the floor
Cooling fracture?
Flow lineations in the cave wall

I haven't posted that?

I can't believe I left my Yellowstone pictures unposted! Let me remedy that!
in the first photo, Bro. Dan Moore pin-points our location on a map of the Yellowstone caldera, just inside the caldera rim. Yellowstone is a playground for Geologists. I had fun watching tourists as they happened upon an expert geologist explaining Yellowstone's volcanism to students. There was an initial captivation; "Ooh! he's explaining the volcanoes!". Then they sat and attempted to decipher the lecture. Words like "isostatic" and "viscous" turned them right away. Poor saps.
Yellowstone Falls at the "Grand Canyon" of Yellowstone. See the yellow stones? That's where the park gets its name.
More staining of the ash flow deposits down the canyon
Hot Springs! You wouldn't want to swim here. The water is that pretty blue color because of the thriving thermophilic bacterium.
Mud pots! The only difference from a hot spring: proximity to the water table.
And one of the main attractions at the park, no, not bison; geysers!

Fluvial Systems

Hearing the word Fluvial should incite one of three reactions: you get really excited, you yawn, or you look confused. That's just the way it works. I happen to really enjoy studying fluvial systems, though anything too extensive can really bore me.
Here's a shot of the Snake River from Henry's fork. Notice the classic cut-bank and point bar deposition; it's about as good of an example of a meandering river as you could hope to find.
Here's a shot of the Snake River at the south fork.
Sedimentary structures near the south fork which are worth looking at

Tuff Stuff; more of the Kilgore

For another day-trip, we went out to the Ririe Reservoir dugway again. I managed to make it home without any significant ash fragments in my eye. These photos show more of the detail of the Kilgore tuff deposits. As seen in the photo above, these are very thick ash deposits.

We used Jacob's staffs to measure thickness of the different ash deposits.

So much pumice!

Another contact further up.

An "intraclast" (the brownish clast just below the pen). Clasts of the underlying bed are included in the subsequent depositional unit, in this case, a "rip up" clast.