Eight years ago this month, I jumped in a car with Lockwood DeWitt for the aboriginal time, and abstruse my best admired assignment in geotripping. You can apprehend a ton of books and blogs. You can booty a few cartography classes. You can do your own geological touring. But annihilation compares to accepting a geologist booty you on a claimed bout of sites they apperceive intimately.
How abundant cartography can you backpack into one abbreviate and backing trip? Turns out, it’s an astronomic amount. And with Kilauea still actuality boring, I ample I’d revisit that alley trip. Don’t worry. There’s affluence of agitable action, alike if the volcanoes accept been asleep for millions of years. Appear one, appear all, and appointment a boundless arrangement of astonishing cartography with us!
Day One: Marys Peak, Corvallis, Oregon
Marys Peak is this long, swaybacked abundance in the Coast Range a Corvallis, Oregon. It doesn’t attending like abundant from a distance, abnormally not if you’re acclimated to ambidextrous with the majestic as heck, broken peaks of the Olympics and Arctic Cascades. It looks serene and gentle, like a candied little old grandmother, beside the adolescent and agitated volcanoes of the Cascade Range. But the affair with allegedly candied and arid old mountains is that they’re hecking deceptive, like that aging octogenarian who consistently bakes accolade for the adjacency kids – with the aforementioned easily that attempt Nazis dead. And again you acquisition out that was aloof one adventure in a continued and agitative life.
Marys Peak has apparent some shirt, y’all. Let’s accept a appointment with her and apprehend some stories.
Hyaloclastite and Slickensides
One of the actual aboriginal stops we fabricated was at this astronomic accept of atramentous rock. This bedrock has been through it. It was built-in underwater, back the basalt erupted erupted and shattered. This actuality is composed of sideromelane, a basaltic bottle formed back mafic bedrock is quenched aback in water; some tiny wee pillows; additional palagonite and some added different things, all anchored calm into a solid mass. Then, back tectonics heaved Marys Peak from the ocean assimilate land, this bedrock was awkward and aching forth faults, abrogation able and acclimatized surfaces accepted as slickensides.
There’s so abundant added cartography at this spot! See Lockwood’s column on it here.
Spheroidal Weathering and Columns
So underwater basalt bedrock flows generally beggarly pillow lavas, but not all angled shapes in an old bedrock breeze are pillows. There’s a prime archetype of this area these columns crop out. Back you accept a jointed bedrock like this, the weathering can advance from assorted admonition and abrasion bottomward the corners, basic accurately angled rocks. This is apperceive as spheroidal weathering. We’ll see after how you can acquaint the aberration amid this anatomy of actinic weathering and 18-carat pillows.
As for columns, the key affair to bethink is that they anatomy erect to the cooling front. This agency you can attending at the way the columns are aggressive and apperceive things about cartography that no best exists! The acclimatization of these columns is difficult to suss out from the absolute exposures, but this breeze may accept abounding an old beck channel. There are added clues cogent us this was a subaerial bedrock flow: can you aces them out?
This acknowledgment is breathtaking. I affirm my affection about chock-full assault the aboriginal time I saw it: a abundance of pillow bedrock aloft addition mountain. Millions of years ago, the flows that birthed these astronomic pillows agitated over a seafloor; today, they abide 4,000 anxiety in the air. The ability of bowl tectonics strikes abounding force here.
The pillows are as beginning as yesterday, and affectation the abrupt differences amid them and rocks asperous into a all-around shape. You can see the alligator arrangement of their skin, agleam with rapidly-quenched agitable glass. You can beam the adorable joints created as they cooled and shrank from the alfresco in – bethink joints basic erect to the cooling front? This is what it looks like back the advanced is all around. Amid the pillows is added of our old acquaintance hyaloclastite. And zeolites accept formed aural and amid the pillows, continuing out abrupt white adjoin the atramentous matrix. There’s abundant cartography at this armpit to accumulate you active for years!
When you accept a agitable island and seafloor advance up aerial into the air, you accept got faults. And abounding of the faults on Marys Peak, like these, are accessible alike to the amateur. Faults can be adequately baby and narrow, like these, or valley-wide zones of ashamed and breakable rock. And it’s forth faults of assorted shapes and sizes that Marys Peak was advance up from beneath sea akin to bags of anxiety in the air.
Oh, people, this is one of the best things on Marys Peak: turbedites! These band cakes of sandstone, mudstone, and siltstone acquaint us so abundant about the mountain’s past. You had dry agitable acreage actuality asperous to anatomy massive amounts of beach and silt. You had abrupt underwater slopes abounding of the stuff. And you apparently had approved ample earthquakes that befuddled it all apart in massive underwater landslides. These bedrock layers are abounding of burst bulb fossils, attesting to the ability of the flows. So very, actual awesome. Who says apparent amber rocks are boring?!
Ah, the actuality “black granite” countertops are fabricated of. This astonishing mafic bedrock formed a blubbery axle aloft the bendable sedimentary layers, and cooled boring abysmal underground. But not evenly! Irregularities in its mineral agreement advance this gabbro absent some of its airy agreeable like baptize absolutely rapidly, abatement the bedrock afore its minute actual olivine could back-react with silica to become pyroxene. Sound complex? The geochemistry of this bean and the belief its mineral crystals acquaint could accumulate you active for a decade.
It’s acknowledgment to the gabbro that Marys Peak stands so tall. Miles of softer bedrock aloft it accept breakable away, a fate the sedimentary rocks beneath would allotment if it weren’t for that heavy, stout accumulation of apparent advantage capping it.
Here in the gabbro by Parker Creek Falls, you can see affirmation of paleomagnetic studies: holes larboard by drills demography cores of rock. Tiny alluring minerals in the gabbro froze pointing alluring arctic (or south, if the bedrock cooled during a time back the poles were reversed). We can abstraction their administration and their amount of affection to actuate things like the above basal admonition of this mass, and almost how aing to the equator it was back it was deposited. Cool!
This abrupt bottomward beck has a lot to acquaint about the analysis of aggressive bedrock layers. And it says it beautifully.
Next up: sidewalk cartography and humongous floods!
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