Saturday, September 25, 2010

Marys Peak Stop 1: Hyaloclastite And Basaltic Sill

Due to logistics and, paraphrasing Robert Frost, a turn not taken, Dana, Intrepid Companion (IC) and I got off to a latish start on Monday and headed up Marys Peak. This wasn't actually our first stop, but it was the lowest stop stratigraphically.  The first time I saw this outcrop would have been fall of 1980, and only after many returns did I find the feature here that is now most interesting to me.
This block is fragmentary, glassy basalt, resulting from a submarine explosive eruption- gentle eruptions (effusive, in geo-speak) would produce pillows, which we'll see at a later stop.  This is much more badly weathered than when I first saw it, but even fresh, the glassy basalt fragments, sideromelane, are generally covered in an orange-yellow-brown alteration product called palagonite- formed when the hot material reacts with water to form a mix of clays and oxides.  I didn't get a good close-up of this, but I did get a couple of samples, so I'll shoot some pictures later and post them to give you a better sense of the texture.  This rock type is called either hyaloclastite, or as I originally learned it, hyaloclastic breccia.  Though it might not be immediately apparent from the above photo, both of the large flat surfaces on the exposure are slickensided- the corner where IC is standing is the intersection of two faults.
Here you can see the striations to the left of IC; they appear to be dipping at about 50-55 degrees.
And here, between IC and Dana's location in the first picture is the other slickensided face: you can see the striations are much closer to horizontal.
Though I didn't get any other photos of the overlying mass, you can see above that it has crude columnar joints.  Dana is getting a closer look at the location of the next photo. Question: is that a flow or an intrusion? How would you tell?
Answer: A flow would very likely have a basal breccia. As the flow advances, the top moves forward, rolls over the toe, and forms the base of the flow. It's exposed to air, cools, and solidifies; as it rolls over the toe and is over-ridden by the advancing flow, it breaks up into a breccia.  The basal part of this mass (largely covered in lichen here) is not brecciated, so one can say with some (though not absolute) confidence that this is more likely an intrusion than a flow.

Look carefully at that last picture, at what underlies the base of the sill.  That is a 2-3 inch layer of sediment.  The sill's base is concordant with that sediment, so it is a sill, not a dike or other kind of intrusion.  Though weathered now, the rock is probably best referred to as a hornfels- a non-foliated contact-metamorphosed sediment.  The fact that this layer of sediment is tilted up also tells you that the whole outcrop has been folded to a dip of about 35 degrees.

To understand another reason why this little layer of mud is important, some background is needed.  The coast range terrane, formally named "Siletzia" after the formation name of this basalt (Siletz River Volcanics), extends from southern Oregon, where the basalt is called the Roseburg Volcanics, up to the Olympic Mountains of NW Washington state, and southern Vancouver Island, where it's called the Crescent Formation.  Oddly, it is older at the northern and southern ends, and youngest in the middle.  The basement basalt of this block is thought to be the equivalent of a Hawaiian-style hot spot sitting atop an oceanic ridge- much like Iceland is today (though smaller in scale).  A unit we visited later is called the Kings Valley Siltstone member of the Siletz River Volcanics- in other words, it's so restricted and so intimately associated with the SRV, that it doesn't merit a formation name of its own. It's considered part of- a "member" of- the SRV. That unit is derived from the erosion of basalt that erupted above the ocean, as part of a Hawaiian Island-like chain.  The eroded basalt was then carried to the ocean and deposited as sediment.  Later eruptions could dump more basalt on top of the sediment, and often did.  In some places the resulting interfingering of basalt and sediment are quite spectacular.

I had probably visited this outcrop a half dozen times before, in trying to find the base of the sill to show someone there was no breccia, I realized this modest little layer of sediment was tucked in there.  It's the earliest indicator I know of of the emergence of these now vanished islands from the Pacific Ocean, at some point probably around 55 million years ago.  Though it's the least visually impressive, and certainly the hardest to find, part of this exposure, it puts a very tasty decorative frosting on what is already a nice cake of basalt.

Followup, Monday Sept. 27: Dana has posted some very nice photos and descriptions as well... I adore that little "baby pillow."

In the shot from Flash Earth below, I think this stop is close to the cross hairs in the middle of the image.  Route 34 can be seen in the lower right (SE) corner, and the outcrop is about 2 miles past the Marys Peak Road turnoff.

Friday, September 24, 2010


Alrighty, then.  Dana has posted a couple of teasers- pretty pictures without a whole lot of discussion.  I have finally managed to at least download my pictures from my camera to my computer, so here's my first.  This is Parker Creek on Marys Peak. This is not where it crosses the main, paved summit road, and where sadly, I didn't think to shoot any photos- I was too busy beating on Marys Peak sill, so you'll have to make due with desk-crop photos and whatever Dana shot.  Rather, this is about a half mile down hill from that crossing, where the gravel road to Harlan crosses the stream.  When I take groups up here, this is my preferred spot for lunch.

The bedrock here is ledge-forming Flournoy formation turbidites, but most of the boulders are the more resistant Marys Peak Sill.  Though there are some lithic features of importance, this spot is mainly about pretty riffles and biology.

I think what I'll try to do for Mary's Peak is put together a post for each stop in stratigraphic (as best as I can tell) order- and what I mean by that parenthetical is that within the seafloor basalt (Siletz River Volcanics), there's not really any good way to tell what's stratigraphically higher or lower other than elevation.  And there are enough faults through the area that I don't consider that especially dependable.

God Frikken' Dammit, Google!

How 'bout you just leave freaking well-enough alone?  I was just fine with the status quo, and I didn't need you to go and dick around with things to accomplish... what?  Super. Now we have an improved preview.  Did you need to screw around with everything else to accomplish that?  And you apparently have decided to play the "Let's rotate the photo on uploads" game again.
Thanks, Google. I love the way you make things easier.

In other news, I've finally caught up with the backlog of stuff in my RSS. If I can figure out how to upload pictures that AREN'T ROTATED 90 DEGREES, I can start posting on my recent geogalavanting.


Thursday, September 23, 2010

Thorsday: Loki's Children

Last week's Thorsday triggered a couple of follow-on posts from the geoblogosphere, namely by Dave Bressan at History of Geology, and a rebuttal from Daniel at Sandbian, discussing the role of Fenris (aka Fenrir), the wolf in the above picture, in causing earthquakes. So I thought for today's representation of characters from Norse mythology, I would find a picture of Loki's children... and I'm very pleased to have found The Baldwin Project, from whence the picture and excerpt below are taken.
Now the Dwellers in Asgard knew that these powers of evil had been born into the world and they thought it well that they should take on forms and appear before them in Asgard. So they sent one to Jarnvid, the Iron Wood, bidding Loki bring before the Gods the powers born of him and the witch Angerboda. So Loki came into Asgard once more. [182] And his offspring took on forms and showed themselves to the Gods. The first, whose greed was destruction, showed himself as a fearful Wolf. Fenrir he was named. And the second, whose greed was slow destruction, showed itself as a Serpent. Jormungand it was called. The third whose greed was for withering of all life, took on a form also. When the Gods saw it they were affrighted. For this had the form of a woman, and one side of her was that of a living woman and the other side of her was that of a corpse. Fear ran through Asgard as this form was revealed and as the name that went with it, Hela, was uttered.
This series started out as a lark, basically to celebrate the enjoyment I found as an elementary schooler with the Norse gods and their tales. But it has resulted in a realization of how much I have forgotten. When Dana came in to town Monday, she brought her book of Norse mythology to lend me- I've already read a bit of it.

Long story short, this series has rapidly evolved from simple silliness to a rekindling of my interest in the tales of Europe's northwest.

Geological Emergency


Wednesday, September 22, 2010

Welcome to Autumn

Also too, it's not just World Car-Free Day, it's the autumnal equinox. Today (ignoring atmospheric refraction and the fact that sunrise/sunset are defined as the moments when the last/first bits of the sun's limbs cross the horizon) day and night are equal lengths. For the next three months, nights will get longer and days shorter. Then ever so slowly, the trend will reverse.

At 70 degrees and partly cloudy, this seems like a very auspicious day for the first day of fall. I'm loving it.

Car-Free Today? Tomorrow?

Via blogger buddy Pyglalia, I'm reminded that today is "World Car-Free Day." I understand and accept that in today's world, for the majority of people, a car is a necessity- at least occasionally. I don't think it's reasonable to suppose that parents in the US, for example, aren't going to need to have personal transportation available at a moment's notice. My own circumstances, while maybe not unique, are certainly unusual, so it would be terribly unfair to judge others' choices based on my own decision to give up on cars more than 20 years ago. I have driven- a lot, by my own standards- since then, but mostly in university carpool vehicles for educational and research purposes. Almost the entirety of my own personal needs have been taken care of on foot.

Commemorative "days" such as this are a little irritating and exasperating to me. I feel they provide a psychological reward for doing something on one day, for which there should be constant and consistent pressure to try to do every day. Some days you can't go without a car, some days you can. Rather than feeling smug for that one day out of 365 on which you figure out a way to go without one, seek ways to make that the norm for as many of them as you can. And don't sweat the days when you need to drive. Don't make it an issue of pride and guilt. Just don't take daily driving for granted. Mark my words: change is coming. Either renewable energy or the demise of personal transportation is coming at us, faster than most can imagine- and the loss of the latter would be tragic.

Wednesday Wednesday

From Mademoiselle Minx

Tuesday, September 21, 2010

Out Again Today

With a bunch of last minute juggling, Dana & companion arrived yesterday a bit after noon, and we headed up Mary's Peak- photos and discussion to follow, though you'll need to check Dana's blog- I think she took many more pics than I. Short story: Sea-floor basalt, sediment derived from and deposited on Hawaiian-type island, then deep-sea, continentally-derived turbidites. Intruded by 1000 feet of bizarre Oligocene diabase with compositional zoning, then cut by later faulting of somewhat nebulous nature. It's a very tasty concoction.

So after a quick date with coffee at IZ this morning, we're off to the coast today. At least part of tomorrow will be dedicated to getting caught up (with RSS feeds), but I'm thinking I've got some fun stuff in the pipe for later in the week.

(Hey, Dana here - no wi-fi on my machine, but when I get home, you can look forward to plenty of photos. ZOMG amazing geology!)

Sunday, September 19, 2010

This is Relevant Today

Pirates needed science, too, from SciAm. I think some of these are a wee bit less serious than others, but stop and think about it for a moment before you click over... if you were a stereotypical sea-faring pirate, what science would you need to know? I'm disappointed the article doesn't mention chemistry and geology, both of which might be useful in deciding which booty to bother with.

Sunday Funnies: Talk Like A Pirate Edition

Luke Surl
see more Political Pictures
Sober in a Nightclub
Abstruse Goose
Photo Collection: Star Wars Art Remix
see more Historic LOL Also, a number of other historical Star Wars pics here.
The Daily What
Decisions, decisions: sex, church or waffles? Gotta go with waffles. Alphaville
The High Definite
Hipster Hitler
Awww, so cute! Ewww, so gross! Aw, so cute... Bits and Pieces
Bits and Pieces
Cyanide and Happiness
funny puns - Fine Chinese in the Federation
see more So Much Pun
Now Stop Saying They Don't Have A Plan
"Now stop saying they don't have a plan." see more Political Pictures
Epic Ponyz
Via The High Definite, a very fun gallery of photos at a shop for time travelers- here's my favorite:
funny pictures of cats with captions
see more Lolcats and funny pictures
Bits and Pieces
The Daily What Abstinence-education-only proponents are confused...
The enemy's use of Slapstick devices such as hidden banana peels was the hardest part of the War with the Clowns.
see more Political Pictures
Asian Pirates (ARR, Maties!) go for the whole kit and kaboodle... Great White Snark
PhD Comics
Fake Science
Sofa Pizza
If your boss asks you if you have a sec, don't say that you have "a lot of secs."
Learn From My FailPundit Kitchen
Sofa Pizza
see more Historic LOL
Abstruse Goose
Medium Large
Senor Gif
Darius Whiteplume's Tumblr
Darius Whiteplume's Tumblr
Married to the Sea, via Blackadder
job lols - Water Change Required
see more Monday Through Friday
The stuff of nightmares, from Regretsy
demotivational posters - SUDDENLY
see more Very Demotivational
Mike Luckovich, via The Intersection
demotivational posters - ATTENTION PASSENGERS
see more Very Demotivational
Hacked IRL
Bits and Pieces
Sofa Pizza
I have never before seem a campaign button that made me wish I lived in Delaware, so that it would make sense for me to wear it. The Daily What
"Rage in Motion," from EpicPonyz
Hacked IRL
Bits and Pieces
Criggo Some people never learn...Cyanide and Happiness