(We’re taking the lazy Trendy-Tacky Table-Top Tree Tactic this year.)
Ok, so the technical name for this is “slickenside,” but I find “slickenslide” easier to remember.
(I loved the concept of slip n’ slides as a child.)
Anyway, a slickenside is created as the two sections of rock alongside a fault move past each other, slowly polishing the surfaces of the rock. This creates smooth, slick rock faces along a fault line. Sometimes you can find “slickenlines” on the slickenside, which are small, directional scrap marks left by the movement.
In the above picture, the slickenside (and fault) cross at about 35 degrees from the left to the right. In the below picture, the slickenside is more difficult to see, but is at about 60 degrees.
That, it should be noted, is the definition of slickenside that I learned on a field trip – if anyone has a more technical definition, I would be really interested to hear it!
Many years ago, I was 13, and hiking in the Grand Canyon with my family. We paused near a French family: a mother, a father, and a boy – a cute boy. He was feeding trail-mix to a chipmunk, despite the numerous, multi-lingual signs to the contrary. Luckily, my mother is fluent in French, and was willing to explain the problem to him.
“Excusez-moi,” she said. “You are not allowed to feed the animals.”
The boy looked at her like she was crazy. “Pouquoi?” He asked, empty hand dangling in the air.
“Well, feeding the animals can make them sick. Also, it makes them not afraid of humans. They can become aggressive.”
“Agressifs?’ he asked – just as the chipmunk lashed out and bit a chunk out of his hand.
There was shouting, and shooing, and bleeding… and my mother, explaining to his mother how to get rabies shots.
The moral here? Don’t feed the animals, or assume cute French boys are intelligent.
I’ve lived in Western Washington for a total of twenty-one years, so it’s really easy for me to answer this month’s Accretionary Wedge (#29!) as posed by Ann at Ann's Musings on Geology & Other Things: "What Geological features about the area you call 'home' do you love? and what do you not like?"
Washington can be divided very roughly into thirds: Eastern Washington, home to the Missoula Flood-carved Columbia River Flood Basalts; Western Washington, with thick glacial deposits and steep stratovolcanoes in the Cascade Mountains; and the Olympic Penninsula, which is an accretionary wedge, with the uplifted Olympic Mountains.
My favorite geological features are the volcanoes. These result from the subduction of the Juan de Fuca plate beneath the North American plate:
Cascades Volcano Observatory
Mt. St. Helens
Now, my least favorite geological features of Western Washington are also the Cascades, because they help cause the massive, constant amounts of rain.
The Olympics create a rain shadow, but they aren’t so high that all the moisture condenses and falls: the rest is carried over the Puget Sound. As it does so, it picks up more moisture, which then condenses as it rises over the Cascades, dropping all over Western Washington.
That’s why it rains 365 days out of the year (or at least feels like it!)
Thus, my Theory of Seattle: the rain nourishes the trees and shrubbery, which grows profusely and blocks out the light. Between the rain and the trees, everyone wants to stay indoors – thus, the major IT industry begins. Between the masses of commuters and the nasty dim weather, rush hour runs rampant. Since everyone codes late into the night and has to get up early to beat the traffic, the immense coffee culture is started. Thus, the population has a Vitamin D deficiency, stares at computers constantly, is always struck in traffic, and gets regularly strung out on coffee, resulting in perpetual depression and tweakiness. Thus leading to the reign of 90s grunge music, which also contributes to the high suicide rate.
That’s my theory, at least. And I’m sticking to it.
I’ll be honest: I’ve had my fill of the dreary rain and endless rush hour.
So, I’m going to study Geology at Boise State University next year!
Lava tubes frequently show fantastic features, and I saw some really cool features while I was interning through the GeoCorps Program with the BLM at Craters of the Moon National Monument and Preserve. Some of the more decorative formations are the result of boiling gases inside the lava. Honestly, I hadn’t seen many of these formations before this internship, so it was very exciting!
It was interesting to learn more about lava: how the tube walls themselves cool, how secondary flows erode the original tube, how both cohesiveness and fluidity contribute to form features, and how the pressure in the flow creates different landscapes (like pressure ridges and tumuli.) Being able to observe a great quantity of lava over the course of three months was highly educational - even if I can’t cite lava facts of statistics, I know more about the characteristics of lava by seeing so much of it.
I know I haven’t given much information on the region’s geology itself, but that’s because I get too darned excited about lava tubes.
As the ceiling of a lava tube is cooling: first the exterior layers, and then the interior. Once the exterior layer has begun congealing, gases in the interior lava can boil, squeezing lava out through the exterior layers. (Kind of like a pasta machine.) As this lava drips down, the sides of the drip cool, leaving the liquid lava inside. This liquid lava can then flow to the bottom of the stalactite, creating a hollow space. Sometimes the last bit of the drip falls off the stalactite, other times it plugs the stalactite up. The left picture shows some stubby stalactites from Craters of the Moon, and the right picture shows some really delicate “soda straw” stalactites from near Mt. St. Helens.
If the lava inside these stalactites drips onto the ground, it can pile up to form a stalagmite. I didn’t see many in Idaho, but the ones I did see were really tall. Unfortunately, I didn’t have a camera that day, but I also saw some good ones in Bend this summer.
These are called “stalagpies” by the local cavers, but are more widely known as lava roses, especially when they have a clearly defined series of concentric rings. I think they look a bit gross, but they can form in a really nifty fashion: when lava boils from under a semi-cooled floor, the pressure of the gases pushes the lava up through the floor. As a result, these are also sometimes called “lava volcanoes.” These are identifiably by their “central conduit,” which can be easily seen in the bottom picture. These pictures are from a lava lake, so this explanation makes sense.
Because these don’t have a conduit, I think this is an example of the other way in which lava roses form: when larger clumps or sheets fall from the ceiling, and pile up, cooling, slumping, and cracking as they do so. (I think the right one is especially ugly – it resembles a miniature Horta.) These pictures are from a different cave than the previous lava roses – so a different origin is plausible.
These are lava helictites! These are created in a manner similar to the lava stalactites above, but the lava is pushed through weak spots in the developing crystal structure, forcing it into a twisted shape. Both lava and calcite helictites refuse to obey gravity.
If you want to learn more about lava caves and their features, here are some great resources:
The Virtual Lava Tube is an easily accessible resource, complete with beautiful pictures. This site is run by Dave Bunnell, editor of the National Speleological Society News. He also published the information in a book called Caves of Fire: Inside America's Lava Tubes, which is gorgeous.
Nomenclature of Lava Tube Features is an older article, but describes a greater number of features than the Virtual Lava Tube, including many different types of stalactites and pahoehoe lavas. It’s available in print form in the proceedings of the 6th International Symposium on Vulcanospeleology, and in illustrated form as An Illustrated Glossary of Lava Tube Features. (I wish I’d found the online copy earlier – I accidentally left my print copy in storage!)
|From the USGS|
|From the USGS|
A few weeks ago, I spent a weekend near Prosser, WA with my parents and their friends. This was their annual bicycle-riding and wine-tasting weekend, so most of my pictures feature middle-aged folks in spandex. Much as I’ve become desensitized to such retinal injury, it seems rude to inflict it upon the internet. I did take some decent travel photos, however:
The last one shows some hop trellises. Washington state produces much of the world’s hops, believe it or not.
This Accretionary Wedge, hosted at Research at a snail's pace, is focused on desk-crops. Normally, this would be very exciting – I have a healthy assortment of rocks. But, unfortunately, I put all my rocks in my storage unit when I moved to Idaho for the summer.
I only remembered about this Accretionary Wedge once I arrived in Oregon with four boxes, none of them containing rocks. Luckily, before I went to Phoenix last week, I was helping clean a bookshelf at my parent’s house in Washington, and happened to take some pictures of my mother’s minerals.
My mother (a painter of caves – seriously!) has a soft spot for colorful minerals and rocks. These are actually examples from her stash of minerals inherited from my grandfather, who was into rock-hounding. My mum has some great childhood stories from these trips, including “Terrifying Mine Experiences Involving Cupcakes,” and “Innocent Encounters with Canadian Mounties.”
I haven’t studied mineralogy much yet, so I’m mainly going to reference that bastion of scientific accuracy: wikipedia.
This Death Tribble is a piece of dogtooth spar, or dogtooth calcite. This usually consists of acute scalenohedrons: twelve triangular faces roughly making up scalene triangles. They need standing water to allow them to grow, and so are frequently found in limestone caves. (My grandfather, I’m sure, found this in a rock shop – he wasn’t a caver, much less a cave-vandal.)
The only spooky thing about orpiment is that it’s a highly toxic cocktail of arsenic and sulfide, originating through the rapid solidification of hot gases at fumaroles, hot springs, and hydrothermal veins. It can also occur as the decay byproduct of realgar, a mineral of a similar composition that is frequently also found in conjunction with orpiment. (I’m wondering if realgar is in this sample, based on its appearance in google images.) Orpiment has historically been used for poision, medicine, and paint pigment; its present uses include semiconductors, firework pigments, and as an ingredient in Indian depilatories. (Perhaps: “Extreme Hair Remover: Now with Arsenic!” ?)
Yesterday, my family flew down to Phoenix to watch my brother graduate from UTI (at the head of his class, no less.) Our plane flight was luckily during the day, so we got an aerial view of some great mountains:
I’ve always wanted to see Mt. St. Helens from the air, and I was so excited to spot it!
In a lava cave roof, hot gases boil and push molten lava through cracks in the roof’s cooled crust. This lava can spooge out of its stalactite and drop to the ground, creating a stalagmite like this. This formation has a really nice metallic glaze to it, and I saw it in a cave near Bend, OR.
Much as the heyday of the columnar jointing meme seems to be past, I’d like to jump on the bandwagon in support of Washington’s columns as championed on Northwest Geology Field Trips.
Washington is home to what I would argue is some of the raddest columnar jointing around, as it’s easily reached and highly extensive. And by “highly extensive",” I mean Spans-63,000-Square-Miles extensive.
These columns (near Grand Coulee, WA) show an unevacuated lava tube.* The arch of columns would have been the tube’s roof, as those cooled and cracked perpendicularly to the cooling surface (the air.) Underneath this is a layer of lava that cooled in the tube, and beneath that are more columns from the bottom of the flow. Above this tube is the middle section (the entablature) that cooled in a different fashion and thus has some
pretty fugly hackly jointing.
Dry Falls, whose walls are composed of columns. You just can’t tell that because it’s so stinkin’ huge from this vantage point.
These columns are the Ellensburg formation, and this exposure is over near Naches, WA.
This is Frenchman Coulee, and is once again composed of columns too distant to see.
Oh, and you know what else Washington has that’s better than anywhere else?
Plaid-clad junkies who don’t shower.***
My advice: visit the Columbia River flood basalts, but avoid Aberdeen after dark.
*At least, that is what an unevacuated lava tube has been pointed out to me as. As always, I could be really incorrect.
***I really like plaid.