The annual variation between summer and winter ice cover is about 10 million square kilometers of sea ice, with around 14 million at the peak of winter cover, and a minimum that approaches 4 million late in the boreal summer. That’s a lot of variation, but that variation is the consequence of the seasons. The amount of annual variation is increasing, however: look at the light gray line for the 1980′s average: that only varied by about 8 million square kilometers of area in a six-month span. In fact, the peak winter numbers are still tightly clustered: there is less variation there than there is to the minimum summer numbers. Compare the spread of the data at the peak and the trough of this dataset. Lastly, there is a clear trend in the decadal data, showing decreasing summer ice cover of the Arctic Ocean. What’s your prediction for the minimum sea ice cover this year? What’s your prediction for the 2010′s average, as compared to the previous 3 decades?

Subscribe to Neven’s blog, and watch as the data unfurls in real time. It’s a fascinating phenomenon to watch from the comfort of your computer screen – both the natural annual variability in this remote system, and the signature of climate change that is driving the system into new territory.

Here’s an example of the brecciation:

Another thing that caught my eye at this outcrop was a lovely instance of percussion marks – the little cone-shaped fractures that form when bouncing bedload (saltating cobbles) slam into stationary outcrops of resistant rock like quartzite.  Take a look:

Can tell me which way is upstream?

This boulder is exotic to its current location. It is typical of medium- and coarser-grained diabase from the Culpeper Basin, a Triassic rift valley east of the Blue Ridge. The main minerals are plagioclase (light-colored) and pyroxene (dark colored).

You can see that a substantial portion of this route was above treeline, and the bit just beyond Cory Pass was indescribably epic. Just raw rock, naked and lifeless, as if it was deglaciated a week before we got there. Here’s a composite panorama view looking into the maw of Cory Pass itself:

Step across the threshold, and a gorgeous scene awaits…

I think this tower is Mt. Louis…(?)

Turning to the right, and looking down the valley… Look at those steep slopes! The phrase that pops into my mind is “sheer declivity“…

Did you spot the little character hidden in that last image? If not, I’ll zoom in on her:

As we walked down towards the bottom of this new valley (towards lunch with two marmots and a pika), we saw blocks of rock bearing multi-pronged trace fossils, which I reckon must be feeding traces:

Based on my reading of Ben Gadd’s book Canadian Rockies Geology Road Tours, I think that this is Cairn Formation dolostone – a Devonian deposit. It has a distinctly petroliferous stink to it when freshly broken – a real nostril-opener!

I’m looking forward to leading 18 NOVA students through this same hike this summer…

Then there is the political entity of Shenandoah County, which runs from Massanutten’s southeastern ridge to the West Virginia border, including the North Fork of the Shenandoah River, but not the South Fork:

Shenandoah Mountain is a ridge in Rockingham County, the next county to the southwest of Shenandoah County:

There’s also a town called Shenandoah, and it’s located on the South Fork* of the Shenandoah River, in a third county, Page, which is one of the counties** that lies between Massanutten’s southeastern ridge and the Blue Ridge mountain front:

* Note that Google Maps has mislabeled the South Fork as the “North Fork” in this screenshot. Weird. I’m not used to them making errors like that.

** The other being Warren County, home of the unwieldily-named Raymond R. “Andy” Guest, Jr. Shenandoah River State Park. Here’s a look at it:

Far from all of this, up in the city of Winchester (surrounded by Frederick County), is Shenandoah University:

Finally, of course, is Shenandoah National Park, which unlike every other place discussed so far, lies in the Blue Ridge physiographic (and geologic) province, not the Valley & Ridge:

I would argue that Shenandoah National Park is poorly named, and would have been better dubbed “Blue Ridge National Park.” While parts of it are in the Shenandoah River watershed, the river itself is nowhere within the park’s boundaries.

My wife and I are planning to move to easternmost Shenandoah County next month, to the Fort Valley (inside Massanutten Mountain). Musing on that place name got me thinking about how many other places the name “Shenandoah” has been applied to. Did I miss any?

Handwritten notes by Ernst Cloos (legendary structural geologist from Johns Hopkins University) on the area I visited last Monday on a field review of the new geologic map of the Elkton East quadrangle by Chelsea Jenkins, Chuck Bailey, Mary Cox and Grace Dawson.

(click on the image to get to a larger sized version on Max’s Flickr page)

That’s the Warah Formation exposed on the Batain Coast of northeastern Oman. This is the thrust front of a thin-skinned fold and thrust belt. I think it’s just lovely!

Max has a ton of other great structure photos on Flickr, he tweets, and he has a blog. Check out his work!

Immediately after lunch, we visited an outcrop in the middle of Naked Creek. You’ll be happy to hear that we all retained our full complement of clothing there. But the rocks were hardly brazen and revealing, either. At first glance, it looked like relatively massive quartzite.

This is the same outcrop where we saw one of the three snakes that the field trip brought us into contact with. The geologists spread out and got up close and personal with the quartz sandstone there…

…We found that if you looked closely, there were some subtle clues that made the outcrop make sense…

Those are Skolithos: trace fossils oriented perpendicular to bedding. They are very common in the Cambrian-aged Antietam Formation, a quartz sandstone that has seen some noticeable deformation.

Since Skolithos are perpendicular to bedding, that allowed us to deduce the orientation of the primary sedimentary layering, and compare it to a widely-distributed cleavage which dipped to the southeast. Overall, the outcrop looked roughly like this in map view:

Just one outcrop among hundreds that went into the map…

It had flattened its head to make it very spade-shaped. The right eye was cloudy – perhaps snake glaucoma? Or maybe it was just getting ready to shed its skin?

I was struck by the bedding / cleavage relationships in this outcrop – both dip to the southeast, but bedding dips more steeply than cleavage. The view in this photo is looking along strike to the northeast:

You know what that means: These beds must be overturned!

Here’s a close-up of the leftmost (northwesternmost) of the beds:

…Sweet: A small-scale structure that reveals a regional-scale situation (e.g., the overturned northwestern limb of the Blue Ridge Anticlinorium)!

I’ll have some other images from this trip to share in the next few days.