About.com Geology

On Ophiolites

Fri, 06 Nov 2009 22:16:47 +0000

Some friends of mine got it into their heads that they wanted to visit an ophiolite. As a reader of John McPhee's geology books, I thought "of course, what could be more distinctively Californian?" But as I researched and visited likely field sites and did some reading, the subject grew more and more complex. So let me share an outline of what my friends and I are contemplating in this new article on ophiolites. They aren't something you can pull over by the road and point to; they must be delineated and inferred.

California has lots of ophiolites. This photo is from the Trinity Ophiolite, but I think I'll take my friends to the Del Puerto Ophiolite.
_{Peridotite, Trinity Ophiolite — Geology Guide photo}

On Ophiolites originally appeared on About.com Geology on Friday, November 6th, 2009 at 22:16:47.

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Wrestling with Rocks

Thu, 05 Nov 2009 22:22:00 +0000

Yesterday I visited the Del Puerto Ophiolite, in preparation for a small field trip I'm planning later this month. Every time I go in the field I return amazed at the energy and insight of geologic mappers. Even though I followed a good field-trip guide, I found it difficult to discern everything on my own (fortunately I'll be seeing it again soon). The work that has been done to advance geology to its present state is immense, and highly skilled, and cumulative over centuries of effort. Things don't reveal themselves in one big "aha" insight.

That's why I can't stand the armchair cranks who blithely push theories like creationism, Earth expansion and abiotic oil, assuring their readers that the scientists have everything wrong. I would challenge any of them to approach a real outcrop.

Wrestling with Rocks originally appeared on About.com Geology on Thursday, November 5th, 2009 at 22:22:00.

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How Long Do Aftershocks Last?

Wed, 04 Nov 2009 14:05:24 +0000

The classroom treatment of aftershocks is fairly simple: An earthquake hits, and then a series of aftershocks occurs that is well summarized by three mathematical expressions called the Gutenberg-Richter relation, Bath's law and Omori's law. The first two relate the aftershocks to the mainshock in terms of number and size (G-R says their numbers rise by an order of magnitude with each unit fall in seismic magnitude, and Bath says the largest aftershock averages about 1.2 magnitude units smaller). Omori's law describes how aftershocks tail off to a steady background rate as the reciprocal of time (that is, 10 years later aftershocks occur at 1/10 the rate).

The great majority of earthquakes and their aftershocks are easy to deal with because they occur near plate boundaries. There the seismic background rate is high and aftershock sequences therefore are short, around 10 years (because the background noise swamps their long tails). But away from plate boundaries the background noise is very low, and also the physics within plates appears to favor extra-long aftershock sequences. In sum, Seth Stein and Mian Liu argue in today's Nature, in places like the New Madrid earthquake zone in the central United States, the seismicity we see today could be aftershocks from earthquakes hundreds of years ago. They wouldn't represent the buildup to the next big one.

If we don't recognize these as aftershocks, they will mess up our models for determining earthquake hazards. To places like Memphis, overstrengthening buildings based on a poor New Madrid zone model is wasted money. In more complex plate settings like China, Stein and Liu argue, even distinguishing these aftershocks would only remove one veil from the mysterious and subtle patterns of deadly quakes like the 2008 Sichuan event.

More:
About aftershocks
Earthquake basics
U.S. earthquake hazard map
China earthquake hazard map

How Long Do Aftershocks Last? originally appeared on About.com Geology on Wednesday, November 4th, 2009 at 14:05:24.

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Peridotite: A New Gallery

Tue, 03 Nov 2009 19:13:56 +0000

After a slow drive last month through the eastern Klamath Mountains, with many stops to take pictures and examine rocks, I now consider myself well acquainted with peridotite. That can be hard to do, because peridotite is almost all deep in the mantle and lower oceanic crust. And most of the peridotite that does make it onto the continents is altered into serpentinite. Of the little that is left, California has the nation's largest share, and most of that is in the eastern Klamaths along the upper Trinity River north of Trinity Lake on state route 3 and Trinity County route 17, the Trinity Heritage National Scenic Byway. Most of the pictures in this new gallery come from there.
_{Peridotite hand specimen — Geology Guide photo}

Peridotite: A New Gallery originally appeared on About.com Geology on Tuesday, November 3rd, 2009 at 19:13:56.

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What's a Geopark?

Mon, 02 Nov 2009 20:47:11 +0000

I've cared about geoparks for several years, so I made sure to attend a session on geoparks at the Geological Society of America meeting, on 19 October. The most important news to me was that the National Park Service is collaborating with the GSA on a formal proposal for establishing geoparks in the United States.

But what is a geopark? It's an entity listed by UNESCO that encompasses a noteworthy geological feature along with the peoples and cultures centered on it. Have a look at the 35 geoparks of Europe. For example, the Reserve Géologique de Haute-Provence calls itself Europe's largest open-air geological museum. The townspeople bake ammonite-shaped pastries and organize tourism and festivals around their fossil heritage.

A brand-new podcast has just gone up from the UK's National Environment Research Council, "Protecting Geological Heritage," that will give you a lively introduction to geoparks from the country that more than any other pioneered the concept.

America's closest thing to a geopark is the recently named Ice Age Floods National Geological Trail, which will be a loose network of roadside exhibits, interpretive centers and cultural activities organized in the enormous region marked by the Missoula Floods in the late Pleistocene, stretching from Montana to the Pacific. But there are lots of other good candidates—all we need is a program.

What's a Geopark? originally appeared on About.com Geology on Monday, November 2nd, 2009 at 20:47:11.

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News from Gentle Kansas

Fri, 30 Oct 2009 19:39:38 +0000

The Kansas Supreme Court ruled today that a county in the Flint Hills region was within its rights to ban large wind turbines to preserve "undisturbed vistas of their wind-swept countryside." Ever since Frank Baum set "The Wizard of Oz" there, Kansas has had a reputation as a flat and desolate place. But the Flint Hills are not only a lush, undulating, never-plowed tallgrass prairie, they're also a prime field area for the students of Emporia University. James Aber teaches there and has put up a thorough guidebook to the rocks, landforms and water of that interesting region. It's just one of the items in my list of Kansas Geology resources.

How have the Flint Hills escaped tillage? I don't know, but the name suggests that they're too hard to plow. I'll bet there's a story, if any Kansas geologists out there would care to comment.
_{Flint Hills, Kansas — Courtesy earlyjc5 of Flickr under Creative Commons}

News from Gentle Kansas originally appeared on About.com Geology on Friday, October 30th, 2009 at 19:39:38.

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Update on Women in Geoscience

Thu, 29 Oct 2009 20:15:48 +0000

The indispensable Kim Hannula, who teaches in southern Colorado and blogs at All My Faults Are Stress Related, was at the GSA annual meeting last week giving a talk to a session on ways to get more women and minorities into geology. There is good news, at least for women: their share of geology degrees is steadily rising and looks like it will reach parity within a generation (to judge from the data gathered by the American Institute of Geology). However, there's still a distinct drop between the masters and the doctorate. And that gap persists, at least in academia, beyond the Ph.D. into the female presence in the faculty. Men typically ask, well, aren't there women "in the pipeline" ready to take their places among the tenured professors? It would be nice if that were true, and the question is reasonable, but the answer is no: Women still get, and feel, some discouragement at every stage as they contemplate and strive for a college career. Read Kim's whole post; it's a good one.

The Association for Women Geoscientists posts a page with lots of published sources and data on the problem of the leaky pipeline. One that I found to be an eye-opener was about what colleges could do when choosing between equally qualified candidates: "Too many times we've heard 'Think of who you will feel comfortable with talking to at the picnic.' This attitude promotes hiring of more people like the majority. Try considering 'Do we have sufficient role models for all parts of our undergraduate population?' " That change to a student-centered viewpoint seems valuable to me.

Ground-truthing

Wed, 28 Oct 2009 22:58:16 +0000

Today I went to another part of my city to search for something shown on the geologic map: pillow basalt. I know what it looks like, so I expected no trouble on that account (unlike, say, gabbro, which may be apparent only under the microscope). But nowhere in that ribbon of land could I find anything like pillow basalt. Either it was mapped during excavations for buildings, or it got covered by freeway construction, or the outcrops have weathered into anonymity, or the map was drawn using aerial photography without sufficient ground-truthing, or I just didn't look hard enough.

A geologic map includes a lot of visualizing based on incomplete evidence; in many localities the map is a hypothesis, not the certainty you expect from a street map.

More:
Pillow basalt
Geologic maps of the U.S. states
Reading geologic maps
_{Ordovician pillow basalt, New York — Geology Guide photo}

Ground-truthing originally appeared on About.com Geology on Wednesday, October 28th, 2009 at 22:58:16.

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The Smell of Crude Oil

Tue, 27 Oct 2009 22:28:35 +0000

Both of the first two comments on my post yesterday, about smells in rocks, referred to petroleum. I think it should be on the geologist's life list to visit a natural petroleum seep. Oddly, neither of the two efforts to compile a "top 100" list (Lisa Rossbacher's or Callan Bentley's) includes that experience. To remedy that, I have two different photo tours of petroleum-related sites. Crude oil doesn't smell like tar or gasoline; it's sweeter and softer. It doesn't smell like it would damage your lungs with long exposure. If you ever find yourself driving through an oil field, pull over, get out and sniff the breeze.

Expose yourself to petroleum:
The McKittrick seep
The Lakeview gusher site
The Davis-Schrimpf seep field
Survey of fossil fuels
_{Crude oil, Santa Barbara, Calif. — Courtesy Matt Cohen, all rights reserved}

The Smell of Crude Oil originally appeared on About.com Geology on Tuesday, October 27th, 2009 at 22:28:35.

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Naïve Minerality

Mon, 26 Oct 2009 16:42:18 +0000

Winemakers and wine reviewers are notorious for ladling on the descriptive words. James Thurber skewered the excesses long ago in a cartoon that featured a sophisticate saying, "It's a naïve domestic burgundy without any breeding, but I think you'll be amused by its presumption." And everyone tastes wine differently, even the same person on different days. But all that said, wine evaluation is a pretty rigorous process with a strict vocabulary. The glaring exception is the set of flavor elements recently lumped under the word "minerality."

None of us has a problem dealing with a wine with "cherry notes" or "silky tannins." No one thinks that actual cherries or silk are involved, just flavors or perceptions that resemble them in some way. But ever since "minerality" came into vogue, the notion that, say, a vineyard set in slate bedrock yields wine with a "slaty" taste has persisted in some circles. In a session at the GSA meeting dedicated to terroir, geologist Alex Maltman told us that "mineral" wines, before the 1990s, used to be described as "lean" or "austere." That basically means "not especially sweet, fruity or aromatic." So I think that "mineral" is an advance because it allows us to note the presence of flavor elements from the mineral kingdom like soil, chalk, wet pavement, dust and other evocative scents, not just note the absence of the usual wine flavors.

The mistake is in thinking that wine corresponds directly in flavor to the ground it's grown in. Chalky soils don't yield wines that taste of chalk, thank goodness. It shouldn't take much effort to separate "minerality" from minerals the same way we separate "fruitiness" from actual fruit. But as I listened to Maltman demolishing naïve "minerality," I found myself wondering about the real smells of real rocks. Limestones and cherts often have interesting smells, but I don't think they're trustworthy guides for rockhounds. Maybe they're just smells of soil fungi or something else unrelated to mineralogy.

Do any of you use smell in the field?

UPDATE: One news story about the session was misleadingly headlined "Geologists debunk soil impact on wine." Blogger Dr. Vino followed up with a more substantive entry on the GSA session on terroir.

Naïve Minerality originally appeared on About.com Geology on Monday, October 26th, 2009 at 16:42:18.

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