Thursday, May 22, 2008

Accretionary Wedge #9: Significant Geologic Events

Welcome to the ninth (late night!) edition of the Accretionary Wedge, everybody's favorite geoblog carnival!

Today, 22 May, is the anniversary of the 1960 magnitude 9.5 Valdivia, Chile earthquake and its associated devastating tsunami, the largest ever recorded. I figured it would be an appropriate anniversary for posting a carnival of entries on significant geologic events, though I intended for the theme to encompass smaller and more personally-significant things in addition to (or, so it seems, in concordance with) the events that changed the world in some way.

What I didn't know when choosing today for posting was that the the Southern California ShakeOut Scenario, a hypothetical magnitude 7.8 rupture on the southern third of the San Andreas Fault, had today as its release date. This future event - because it is a when rather than an if - is already high on my personal list of most significant events, since fear of precisely this kind of thing got me into reading about things geological when I first moved from Virginia to California, and since that reading showed me why I have always had at least a background interest in the way the Earth works, and since that in turn lead to my whole crazy change of academic directions. This is one of the reasons the 1906 San Francisco quake fascinates me so much - that there will surely be reflections of it in what eventually happens on the southern San Andreas. I know more about the San Andreas now, its pattern of destruction is less mysterious to me than it was in 2006, and it will be a focus in my MS work, but this kind of disaster scenario still scares me. I'm hoping that, if it happens during my lifetime, it will be significant to me because of understanding and survival, not because it's my last geologic event. Yikes.

But enough about me. There was a prolific response to this theme, with discussions of events long in the past to events personally experienced, precisely the kind of response for which I hoped. Enjoy!

The Lost Geologist understandably has trouble picking a single most significant event, when there are things like meteorite impacts and global glaciations to consider, but he ultimately focuses on the personal realization that Everything is Interconnected.

Callan Bentley of NOVA Geoblog writes a kind of meta-Accretionary-Wedge post, considering two such formations, one west coast and one east. This comparison of California and DC deepened his perspective on his local geology, and highlight the message that Geology Repeats Itself.

Tuff Cookie, of Magma Cum Laude, is also a fan of subduction zones. The subduction of the Farallon Plate is fascinating in and of itself, but is particularly important to Tuff Cookie because it created Utah's High Plateaus, the stuff of which Senior Theses are made.

Living through a major earthquake, particularly if one came close to not making it through, is a scary kind of significant. Kim, of All My Faults Are Stress Related, has every good reason to reprise her Loma Prieta story from Accretionary Wedge #2.

Andrew Alden also has a chillingly cautionary Loma Prieta story in his Oakland Geology Blog, which describes how the Quake of '89 permanently changed the city of Oakland, and his personal connection with earthquakes.

Over at Geology Happens, the runoff from the Rockies is both a herald of spring and a show of the power of big water.

Despite her emphatic declaration that she refuses to pick one out of her set of pet geologic events, Green Gabbro's Maria focuses on the scouring of Fossil Gorge, a 1993 Mississippi River flood that exposed a 375 million year old ecosystem on the one hand, while engulfing hapless Iowan buildings on the other.

Hypocentre's post leaves the Earth itself, though not without taking a chunk of the planet along. He cites the impact that formed the Moon as being key to the development of the Earth's rotation, core, tides, and tectonics.

Silver Fox, of Looking for Detachment, also had some trouble narrowing the prompt down to a single event, or group of events. In the end, though, she cites the tectonic shaping of the American West, which in turn shaped her geological career and the place she calls home.

On a similar train of thought, Geotripper also had a hard time narrowing things down, but came back to the formation of the Grand Canyon as being an event that shaped a career in addition to a landscape. What a fantastic place for a first ever geology field trip, if I do say so myself!

Brian, of Clastic Detritus, is also taken with the American West, though in its Cretaceous wet stage, rather than its current desert state. He describes the Western Interior Seaway, the paleogeographic puzzle it poses, and the geological epiphany that puzzle-solving was for him.

Ole Nielsen, of Olelog, goes beyond the alteration of an entire city to the near annihilation of the Earth's entire human population. If the eruption of Mt. Toba had been any bigger, who knows if any of us would have had ancestors enough left to be sure that we would be here blogging today.

And that's all for this time, folks! Thanks for the excellent entries! Next month's wedge is, I believe, going to be hosted by John van Hoesen, at Geologic Musings in the Taconic Mountains, so keep an eye peeled over there for the next prompt and deadline!

3 comments:

Tuff Cookie said...

Great job, Julian! This AW will be an excellent place to send people to when I get to field those "why would anyone want to be a geologist?" questions.

Silver Fox said...

Yes, thanks for putting this all together - it's a great Wedge!

John Van Hoesen said...

The latest request for the Accretionary Wedge is up here:

http://gmcgeology.blogspot.com/2008/06/accretionary-wedge-call-for-posts.html

Deadline for submissions is June 15th, have fun!!!!

John