Wednesday, August 24, 2016

Geo 889: Stranded Terrace II

A shot from nearby yesterday's, which zooms in a little closer to the small remnant of stranded terrace deposits. I like the framing of the foliage and old man's beard.

Photo unmodified. July 21, 2016. ZoomEarth location.

Tuesday, August 23, 2016

Geo 888: Stranded Terrace Deposits

Overlooking a small cove just north south of Sunset Bay, one can fairly easily spot the buff-colored layer of semi-consolidated sand, about six feet thick, overlying the tilted Eocene beds of the Coaledo Formation. It's a beautiful spot, and a nostalgic one for me. When I was young and hale, I clambered down into this cove a few times; there are some gorgeous sedimentary structures in the strata here. But at this point, with poorer balance and limited endurance, there's no way I'll be down there again unless a decent path is constructed. I have no reason to think that has been, or will be, done. The routes down were precarious, with tree roots and vines, mostly, as the only hand-holds, and the climbs back up were often scary, or worse if I had taken samples (one ten-pound block, in particular, comes to mind).

There's a modest fault running through the cove; this is particularly apparent in the ZoomEarth satellite image. I'm pretty sure the sandstone bed running from the middle toward the lower right is the same as the one on top of the tilted slab on the middle left.

However, the feature the sprang out at me on this trip was the isolated bit of terrace material on top of the anvil to the far right. There a tension between subsidence and uplift in this area. On a scale of millennia, there can be subsidence, as demonstrated by the dead tree stumps on the inner south shore of Sunset Bay. On a longer scale, tens of thousands to millions of years, terraces like this (and six more higher up tentatively identified) clearly show a pattern of tectonic uplift. That little pile of stranded terrace deposits will soon fall as the latest victim to the ongoing ups-and-downs of this area's coastal elevator.

Photo unmodified. July 21, 2016. ZoomEarth location.

Monday, August 22, 2016

Geo 887: Wave Refraction

As an ocean wave approaches shore, it reaches a point where the decreasing water depth causes it to slow and pile up. Wave frequency (number of waves in a period of time) remains more or less unchanged, but wavelength (distance between waves) is shortened, and amplitude (height between crest and trough) increases. Shortened wavelength and increased amplitude finally renders the wave unstable, and it breaks.

The seas on this day at Sunset Bay were quite calm, but the narrow opening to the bay at low tide meant that what waves were coming in off the ocean were well defined. Despite the curvature of the shore, you can see the waves are approaching it nearly perpendicularly across its length (despite the pesky botanical material in the way).

Photo unmodified. July 21, 2016. ZoomEarth location.

Sunday, August 21, 2016

One Year From Today

The blue line across the middle represents the mid-line of the August 21, 2017 total solar eclipse. The shaded area around that line represents the area of totality, where the sun's disk will be completely obscured for a period of time as the moon passes in front of it. The closer an observer is to the mid-line, the longer the sun will be obscured.

I've been excited about this for years; I've never seen a total solar eclipse. I've seen partials that were total or annular elsewhere, but I've never been in the path of totality. For viewing, all I really need to do is be awake and standing in view of the sun, but I'd like to get to a decent elevation. I understand that if you're in a spot with a good east-west vista, you can see the shadow of the moon approaching and receding before and after totality. In Corvallis, the umbral speed will be 1.310 km/sec, or 2929 miles per hour-- which is to say, the fastest predictable thing I will ever see. This interactive map (from which the above screen shot was taken) is the best resource I've found for planning, with extensive details about the event. Simply click the crosshairs on a point of interest, and a table of data will pop up, telling you everything you could want to know about the eclipse at that position.

I have some ideas about where to watch it, but I hope to have opportunities to do some scouting between now and then. It may be that I can get up to the Santiam Pass area and do geology for much of the remainder of the day. In the end, I suspect I'll play it by ear. This time of year, fires and smoke can muddle an otherwise glorious view. However, the chance of rain- or even heavy clouds- in mid-late August is next to nil.