Feature article in October Earth Magazine - fossilized shockwaves

For Earth Magazine's October 2011 edition, I wrote a feature story about the discovery of the Santa Fe impact structure in New Mexico. To see the field evidence of this discovery first hand, I followed retired geologist Tim McElvain out into the Precambrian rocks of the Sangre de Cristo mountains. The crux of his geologic field evidence was finding shatter cones -- rocks that are deformed in a very special way during large meteorite impacts -- and preserved in only a few places on Earth.

Here's a link to the online version of the article:
http://www.earthmagazine.org/article/santa-fe-impact-crater-discovery-series-fortunate-events


Below is an annotated photo I took of a Santa Fe shatter cone outcrop that formed in Precambrian schist. For reference, the field notebook I used for scale is about 4 inches tall. You can see the yellow outlines I made around the most prominent shatter cones -- there are millions at this location -- ranging from meter-sized to millimeter-sized.

Shatter cones are fractal, which means their telltale shape repeats all the way down to the microscopic scale. The cones "point" to the center of the impact structure or crater, which is where the meteorite hit the Earth. A shockwave was created by this massive meteorite impact, and caused permanent deformation (shatter cones) to the Precambrian schists as it passed through the bedrock.

So when you see a shatter cone you're basically looking at a fossilized shockwave!

Unfortunately, no one has discovered an impact crater here in Washington State, though it would be nice to have a local one to investigate. More people to get  out and take a second look at road cuts, upturned beds, and gravity anomalies around the state. If you think you've found something, shoot me an email and I'd be happy to take a look.

You can check out all the confirmed meteor impact sites worldwide at this website: http://www.passc.net/EarthImpactDatabase/index.html

Earth Magazine (http://www.earthmagazine.org/) is published by the American Geosciences Institute.

Fort Worden Beach, Port Townsend and Tamanowas Rock, Chimacum, WA

My trusty field hand and I had a busy week. At Fort Worden State park we practiced proper hand lens technique and enjoyed the Port Townsend Marine Science Center's geologic exhibit.

I've been to the Marine Science Center's Geology Exhibit several times -- I recommend it as an excellent primer for learning about local geology: glaciers, plate tectonics, local fossils, ice-transported rocks (erratics) and beach sand. The gift shop sells an excellent fold-open water-proof guide for beach pebble identification.

Later, we visited Tamanowas Rock. This monolith is a sacred S'Klallam site in Chimacum, now under Jefferson County Land Trust preservation. The honeycomb (geology speak = tafoni) weathering pattern give the cliffs a very interesting texture. A volcanic block and ash flow eruption 30 million years ago created deposits of dacite/adakite composition. The trail is very steep, so be prepared. Dr. Jeff Tepper gave a great lecture on Tamanowas Rock Saturday June 11 http://www.saveland.org/Events/Event_Detail.aspx?processID=81

On the hike out, I saw several gorgeous foxgloves. Spring is here -- and with only a week left -- just in time.

May 12 Geology talk at East Jefferson Rotary Club

On Thursday May 12, I'll be giving a 30-minute powerpoint presentation on the Geology of Port Hadlock, Chimacum and Irondale to the East Jefferson Rotary Club held at the Tri-Area Community Center.

This part of East Jefferson County is home to excellent beach exposures of glacial deposits, roadcuts showcasing Crescent basalt, limonite bog iron ore deposits, a monolith and more.

The local Crescent basalts have excellent vuggy yellow calcite crystals. (Photo courtesy WashingtonMinerals.com, see link for more Beaver Valley basalt quarry minerals: http://www.washingtonminerals.com/bvq.htm)

Irondale is named for the historic Irondale iron smelter, which produced iron between 1881-1919. The first iron produced at the smelter was pig iron, made from limonite iron ore (bog ore) deposits in Chimacum Valley.

The Chimacum Valley is an active organic farming community, with many exposures of Crescent Basalt visible from Highway 19 (Beaver Valley Road). There are two operating basalt quarries in the Port Ludlow and Shine areas where basalt is mined and crushed, to produce local road aggregate and landscaping rocks.

Local drinking water is supplied by municipal wells that tap into groundwater in the Sparling aquifer, a glacial deposit of coarse-grained Vashon Advance outwash. A talk dedicated to groundwater resources will be held by the local PUD on Wednesday May 25, 2011 at 6 pm, at the Tri-Area Community Center.

Tamanowas Rock - also called Chimacum Rock or Anderson Rock - is a monolith that stands 400 feet above sea level adjacent to Anderson Lake State Park. This rock is composed of adakite lava, which is a rare sort of andesite lava that is made by subducting and melting of an ocean spreading ridge. http://nwgeology.wordpress.com/the-fieldtrips/tamanowas-rock-chimacum-olympic-peninsula/

You can hear a presentation on the volcanic deposits of Tamanowas Rock by Dr. Jeff Tepper from the University of Puget Sound, Saturday June 11, 2011 from 1-2 pm at the Tri-Area Community Center. The talk is sponsored by the Jefferson Land Trust. http://www.saveland.org/Events/Event_Detail.aspx?processID=81

Ruby Beach, Olympic Peninsula

Ruby Beach in January is wet. Probably the other months too. It's located on the west coast of the Olympic Peninsula, about 30 minutes south of Forks.

Looking at rocks exposed on the wave cut beach. There were massive surges at the river delta as the tide ebbed and flood waters came down the river: the water level in this photo could rise by a foot in 15 seconds.

Pink flecks of the mineral garnet give the beach sands their famous flashes of color. "Ruby" is a mistaken moniker -- ruby is the gem name for the mineral corundum -- which isn't present at this location.