Tuesday, April 15, 2014

Geo 730: April 15, Day 471: Trolling Depoe Bay

Under the Highway 101 bridge, at the southern end of the Depoe Bay metropolitan area, one can see the narrow neck of the channel into the eponymous bay. I can't tell, at the resolution of the photos I have, what form the basalt is taking here. I suspect it's predominantly breccia, perhaps with some isolated pillows, based on the patchy white spots. The latter are almost certainly composed of zeolites and/or calcite, which are signature accessory/secondary minerals with mafic to intermediate lavas in wet environments.

Photo unmodified. July 10, 2012. FlashEarth location.

Monday, April 14, 2014

Geo 730: April 14, Day 470: Depoe Bay Geology

Not much "geology" to be seen in this photo, aside from a knob of basalt in the lower left. But make no mistake, there's a lot of geology going on here. I had long assumed (due to pillow basalts I'll show in coming days) that in this area, it was Siletz River Volcanics, the basement rock of the Coast Range. However, given the proximity of this area to Otter Rock and the ring dikes there, it should come as no surprise that this is actually Columbia River Basalt, of Miocene rather than Eocene age. There are flows of two distinct ages, separated by an interval of sedimentation referred to as the sandstone of Whale Cove. Up until the 80's, these Miocene basalts were thought to be local eruptions, though that started to look problematic with the development of Plate Tectonic theory, and even at the time, the close chemical affinity to the CRB was recognized. By the mid-late 80's, a number of the more northerly coastal occurrences were confirmed as CRB, and now, the Miocene basalts along the northern coast, down to Seal Rock, are accepted as flows that made it all the way from eastern Oregon to the coast.

The bay itself is something of an oddity: it's quite small, at six acres, with a very tight entry, as we'll see in coming days. It's clear that this was not eroded by wave energy, and there's no major drainage through it, as is the case with most of the larger estuaries on the coast, but only a pair of fairly modest creeks. A key insight for grasping the nature of most of Oregon's harbors is that during the Pleistocene, sea levels were roughly 100 meters (~330 feet) lower than now, as ice sheets covered much of the northern continents. "The shore" would have been miles outboard from its current location. The implication is that erosion by the two creeks- the confluence of which is submerged by the modern bay- could have a steeper gradient and greater competence than one might assume given all the standing water that one sees today. At the end of the last glaciation as ice sheets melted off, the rising sea swamped what I picture as a steep, narrow canyon, creating a small, but very well protected, pocket bay.

There is a publication in The Ore Bin, from 1971 (PDF), that outlines the geology of the area. With the caveat that the "Miocene volcanoes"are now interpreted as flows from hundreds of miles away rather than local eruptions, it looks pretty good today. The following map is on page 14 of that document.
 
Photo unmodified. July 10, 2012. FlashEarth location.

Sunday, April 13, 2014

Sunday Funnies: GAH! Edition

Senor Gif
Senor Gif
Skut Farkus
Bad Newspaper
Bizarro
"Me participating in a group project" Tastefully Offensive
Surviving the World
 "1927 was a rough time for donuts." Wil Wheaton
Tastefully Offensive
Are You Talking to Meme?
Funny to Me
Texts From TNG
Very Demotivational
Girls With Slingshots
"This is what happens for real when I can’t find the right words." Six more examples at Funny to Me
Are You Talking to Meme?
The Far Left Side
Satire or Real? Who knows? What Would Jack Do?
Funny to Me
Bad Newspaper
Very Demotivational
Cheezburger
Texts From TNG
Cheezburger
Julia Segal
Funny to Me
Abstruse Goose
Electronic Cerebrectomy
See Mike Draw
Very Demotivational
Little Harley Things
Eric's Comics
1111 Comics
Bits and Pieces
Unearthed Comics
Bizarro
Derpy Cats
Tastefully Offensive
The Far Left Side
Blackadder
Fowl Language Comics
Very Demotivational
Medium Large (Incidentally, if this is all you've heard about this incident, it appears the film misrepresented a number of well-meaning people. KM issued a statement on the misuse of her talent on Facebook.)
Funny to Me
Partially Clips
Cyanide and Happiness
 What Would Jack Do?
Tastefully Offensive
Happy Jar
Tastefully Offensive
Very Demotivational
Texts From TNG
"Get down, Mr. President!" Cheezburger
"One donut to rule them all" Mirach Ravaia
 Savage Chickens
Doghouse Diaries
"Facehugger" Animals Being Dicks
This Modern World
Senor Gif