Thursday, December 6, 2018

Wait a Minute...What Happened to the Rocks I Picked Out?

Something kind of extraordinary happened on campus this week. I was pausing between classes and saw a large truck and a crane downstairs in the staging area for the Great Valley Outdoor Nature Lab. The crane was dumping gigantic rocks onto the ground. "My" rock collection had arrived!! You might remember that early last month I went 'rock collecting' in the Sierra Nevada foothills for the rocks that will be part of the displays and landscaping of the outdoor. All 60 tons or so...
My response about their arrival on campus was predictable...

But if you remember the scene in "Elf" when Buddy thought Santa was in the store only to discover he was a fake, well, I had that moment too. I saw that something was off about the rocks I had selected. Something was different about them. Below was the rock that I selected a month ago, when it was 85 degrees out, and rain had not fallen in months...
And here (below) is the rock they claim I picked out. This after nearly two weeks of rain and cooler temperatures. This rock is clearly on a PALLET of LIES!

Well, okay, maybe it isn't on a pallet like the others, and maybe it is the same rock I picked out. But you can now see one of the main reasons I picked it, and why it will be sitting in a position of honor by the entrance sign to the outdoor nature lab. Not only is it a unique rock that is found in our region (the latite of Table Mountain), it is also a miniature ecosystem of mosses, lichens, grass, and other organisms. To see it, just add water!
In any case, we now have an astounding variety of the rocks that are found in our region. There is marble from the Calaveras Complex, the host rock of the many caverns that are found in the Sierra Nevada foothills.
There is a gigantic chunk of the quartz from the Mother Lode veins, the source of the gold that played such a huge (and devastating) part in the history of California. Sorry, no visible gold (although I'll keep looking).
One of the most striking rocks are the "tombstone rocks" of the Foothills Terrane, large fins of slate and phyllite that were once mud and silt on the ocean floor. The rocks were crushed against the western edge of North America, metamorphosed, and tilted vertically. We'll be putting them in the ground in the same vertical orientation. It will be a dramatic sight at the southern entrance to the lab.

The next step comes at the end of the week. I'll get to help direct the placement of the rocks! I'll try not to be insufferably picky..."Could you rotate that one about four inches? Great! Wait...I liked it better the way it was...". An update will follow.

Tuesday, December 4, 2018

Why did the Road Cross the San Andreas Fault? 16 Years of Geologic Change (an Update)

I've been leading geology field studies trips to lots of places in the American West for 30 years and started to take digital pictures in 2001. I sometimes struggle to find new things to photograph when I visit a place for the 30th time, but in some cases it is not a problem. There are geologic changes that happen on a yearly basis, and with sixteen years of photos, the changes become obvious. This is a continuing update from a post in 2013, and I'll probably continue updating for the foreseeable future.
Highway 25 in the California Coast Ranges connects the town of Hollister with the access road to Pinnacles National Park (formerly Pinnacles National Monument). Along the way the highway crosses the San Andreas fault in a section where the fault creeps an inch or so each year (36°35'54.27"N, 121°11'40.19"W). Most years we've stopped to have a look at the effect the movement has on the pavement. In 2002 and 2004, the damage was obvious.
By 2008 someone had patched the road, and no fault motion was evident.
Little damage was evident in 2009 either. But by 2010 cracks had begun to appear as the fault stressed the pavement.
The fact that the fault creeps in this region is a good thing. It means that stress is not building along the fault surface, but instead is being released gradually. The sections of the fault to the north and south of the creeping section are locked by friction, and are building up the ominous stress that will eventually produce quakes with magnitudes in the range of 7.5 to 8.0. The quakes are coming and we need to be as prepared as possible.
By 2012, the road had been completely repaved, and  yet the shearing was already evident.
It became even more pronounced by 2013 and in 2014. Just by chance, the person working as a scale was the same individual as in 2004.

In 2015 the fractures were moderately larger. They'll need to start thinking of road repairs before long.
In 2016 Laura once again provided scale, as she did in 2014 and 2004.
Here in 2017, long-time trip volunteer Mary provides scale. The cracks in the road are just a bit larger, but they didn't look appreciably different than the previous year except for a twist (pun intended).

And so we come to Sunday's (Dec. 2, 2018) look at the road. The break to my eye seems more continuous. It's now been six years since the road was completely repaved.

Last year the paint was deformed (twisted), but not split (below).
The offset paint strip reminds me of illustrations of elastic rebound theory, the idea that stress builds up on a fault line over time. In that model, the land on either side of the fault is distorted over time until the frictional resistance is overcome and the rock snaps back to its original shape. That won't be happening with the paint. Last year in 2017 I said "if they don't repair the road (as they often do; see above), it will probably show a clear break by next year." Here's what transpired:

First, a close-up on 2017's center stripe...
And here's how it looked on Sunday, Dec. 2, 2018:
As predicted, the break in the paint is complete!

So now we await next year's trip...

These little changes that happen at a rate visible in human lifetimes add up to huge changes when multiplied by thousands or millions of years. The nearby eroded volcano of Pinnacles National Park has been displaced 195 miles (315 kilometers) in the last 20 million years or so by movement along the San Andreas.

Monday, December 3, 2018

How Much Can Happen in a Minute? The Anchorage Earthquake of 11/30/18

The Anchorage Alaska 7.0 magnitude earthquake as measured at Modesto Junior College

Attention must be paid. If you are one of my friends or readers in California or Nevada, you need to watch this. If you live in Oregon or Washington, you need to watch this. If you live in any place where earthquakes are a serious possibility, you need to watch. Why? Because when your time comes and you must undergo the ordeal of a major earthquake, you need to be ready, both for the duration of the quake itself, and in the aftermath. These people handled things pretty well.

In a nutshell, realize that your building will remain standing and you won't have time to get out of it anyway. What you'll need to do is not panic and take shelter from debris that could fall from the ceiling or walls. Be a helper as Mr. Rogers would put it and reassure the others around you so they won't panic either.

In the aftermath, check yourself and others for injuries. Get to a safe place, as there will be aftershocks. Stay off the phones; they should be used for emergencies only during the first hours after the quake. You should already have prepared a first aid kit for your home and your car, and you should have water supplies in both places as well. You should also have a plan in place for reuniting your family. This is often best accomplished by having an out of the region relative being the contact person.
Source: U.S. Geological Survey

The most important thing you can do right now is education yourself about the earthquake risks in your home region. The U.S. Geological Survey and state agencies are always a good place to start. You may live outside of California, but you might be surprised at the possibilities for damaging quakes in other parts of the country.

The damage in Anchorage was extensive and the residents have my prayers and best wishes. But it is very notable that Alaska has had high architecture standards because of the magnitude 9.2 quake in 1964, and it paid off. At the last report I heard there were no deaths and few injuries. California also has high standards; in most cases you can trust the buildings will weather the quake. Just do your part to make sure the people do okay as well.