North Salem Balanced Rock

There is a unique geologic feature in the Hudson Valley which, for some reason, I have never visited in all the years I've been in the area.  I drove out there this past weekend to view it with my family.  It's called Balanced Rock and it's in the town of North Salem in Northern Westchester County near the Connecticut board (a few miles south of I-84).

Balanced rock is easy to find and visit since it's located right on the side of the road with good parking on town property with a nice interpretive sign.

As the sign says, geologists call this an erratic.  I personally don't think it's a man-made dolmen despite its striking appearance,  That doesn't mean Native Americans didn't consider it a sacred site, they may have, but I'm not aware of any archaeological evidence for ancient activity here (especially by seafaring Celts!).

The boulder itself is granite and a number of web sources state that it's 16 x 14 x 10 feet in size (I didn't measure it but it seems about right).  Let's simplify to 5 x 4 x 3 meters.  That's 500 x 400 x 300 cm or 60,000,000 cm³.  Granite has a density of about 2.7 g/cm³ which gives us 162,000,000 g or 162,000 kg of mass.  That's about 178 tons or three times what is says on the sign (my estimate would be an upper limit since the rock isn't a perfect rectangular box).

However much it weighs, it's a massive rock.  The rock is heavily weathered but a close look at the surface in places shows that it's a pink granite (the pink minerals are potassium feldspar crystals).  Granite like this is found a bit north in the Hudson Highlands.

The boulder is resting securely on five other rocks (possibly Wappinger Group limestone/dolostone).  If you visit, and want to crawl underneath, clear the spider webs before sticking your head in there (I speak from experience).

Despite how precarious it looks, the rock is very stable.  Even my kids couldn't push it over!

So, how did something like this form?  Well, all over the Hudson Valley of New York we find big boulders sitting around (really, all over the northern parts of the United States).  They were picked up and transported by massive continental glaciers during the last ice age (actually, several advances and retreats of glacial ice between 2 million and ten thousand years ago).  When the glaciers melted, these rocks, some as large as houses, were dropped out and are known as glacial erratics (I'll show more examples of glacial erratics around the Hudson Valley in another post).  While most rocks were dumped onto the ground, this one happened to be dumped onto a few other rocks forming the unique structure we see today.

Here's a neat example of another balanced glacial erratic from near Valtola, Finland that's even larger than the North Salem rock.  Called Kummakivi, which translates as "strange rock" from Finn, it's associated with legends of trolls and giants (of course!).

While some websites claim "There is still no scientific explanation for how the rock ... has wound up in such a perplexing position", they are full of shit since any geologist will tell you it's a glacial erratic - the bottom rock even has nice glacial striations (scratches from rocks carried in the bottom of moving ice sheets) clearly visible in many of the photographs of the site.

Back to the New Salem rock.  If you search the web, a lot of the information you'll see about Balanced Rock is from New Agers who credulously claim it's a dolmen.  Dolmens are megalithic tombs found in various places in Western Europe (most notably Ireland).  They typically consist of flat rocks supported by three or more uprights.  While superficially looking like a dolmen (not much, in my opinion, since the proportions aren't right), it's far likelier to be a glacial erratic.  Nevertheless, I tried pulling some psychic energy from the rock.

 

My chakras are still tingling.

Indian Pipe

While hiking in the Catskills last Sunday I saw a distinctive planet called Indian pipe (Monotropa uniflora).  While it superficially looks like a fungus, it's actually a flowering plant which lacks chlorophyll (hence the white color).

So, with no chlorophyll, this plant can't photosynthesize.  Plants like this are called saprophytes and, like fungus, obtain their nutrients from decaying plant matter.  This explanation is overly-simplistic, however, and the true relationship is far more interesting.

Throughout the forest floor, threads of fungus, called hyphae, are interacting with tree roots in a symbiotic relationship called a mycorrhiza.  Fungi get sugars from the trees (via photosynthesis of the trees leaves) while the fungi help pass minerals to the tree which they can more efficiently harvest from the soil.  It's a mutually beneficial relationship.

The Indian pipe, on the other hand, exploits this relationship in a parasitic way.  It taps into that underground network of fungal hyphae and extracts both minerals and sugars from it (the sugars that originally came from trees).  It most-likely does this by exploiting the same chemical cues that the fungi and trees use in their symbiotic relationship.

Indian pipe belongs to the Ericaceae family of plants - the same family as cranberries, blueberries, azaleas, and rhododendron.  So why did Indian pipe lose its chlorophyll?  Well, at some point, ancestors of this plant figured out how to tap into that fungal food source.  This allowed the plant to give up the costly process of photosynthesis and grow on the densely shaded forest floor where there was less competition from green plants.

By the way, should you encounter Indian pipe in your wanderings in the wood, don't bother picking it - it quickly turns black.

Other names for Indian pipe include corpse plant and ghost plant.  It was one of poet Emily Dickinson's favorite flowers and strikingly graces the cover of a posthumous book of her poems.

The flowers on the book came from a painting given to her in 1882, a few years before her death, by her neighbor Mabel Loomis Todd. Dickinson responded in a thank-you letter:

"That without suspecting it you should send me the preferred flower of life, seems almost supernatural… I still cherish the clutch with which I bore it from the ground when a wondering child, and unearthly booty, and maturity only enhances the mystery, never decreases it.”

Some have compared Dickinson, the reclusive lady dressed in white, to the pale Indian pipe living alone on the melancholy shaded forest floor.

 

'Tis whiter than an Indian Pipe —
'Tis dimmer than a Lace —
No stature has it, like a Fog
When you approach the place —
Nor any voice imply it here
Or intimate it there
A spirit — how doth it accost —
What function hath the Air?
This limitless Hyperbole
Each one of us shall be —
'Tis Drama — if Hypothesis
It be not Tragedy —

Waving at Saturn

Below, to the left, is one of the images Cassini took of Earth from Saturn on July 19 (I talked about this last Friday).  On the right, is an image of the Earth-Moon system from the Messenger spacecraft (currently orbiting Mercury) taken on the same day.  From Saturn, the Earth is 898 million miles (1.44 billion kilometers) away and from Mercury it's 61 million miles (98 million kilometers) away.

 

These images are pretty amazing.  On that bright speck in each of the them lives, and has lived, every human being ever in existence.  The furthest any human has ever traveled is to that other smaller speck next to it.

At the very moment Cassini was imaging this Earth (5:30 pm EDT), my daughter and I were on that planet facing toward Saturn (148° azimuth, 31° altitude in the mid-Hudson Valley) and waving hello from my backyard.

Greetings from Earth!

 

[I rewrote this post because I made an error in the original confusing the Messenger and Cassini images - sorry about that!]

I wish I could make morons disappear...

Lest you think I make this shit up, check the links.  Dan Delzell is a pastor at Wellspring Lutheran Church in Papillion, Nebraska.  He's also a regular columnist for a publication called the Christian Post.

Delzell wrote a bizarre little column last week - "The Illusion That Seduces and Bewitches Magicians."  In his article, he wrote:

"I had never heard of the magician, Dynamo, until I read about how he floated alongside a double-decker bus in London recently. I watched the video. Personally, I think it was legit. I believe this was a paranormal event and an authentic example of levitation."

Delzell continued...

"Whether the levitation is experienced by young girls playing a dangerous occult "game" at a slumber party, ("Light as a feather, Stiff as a board") or by street magicians as shown on YouTube videos, paranormal things happen when people engage in practices that are rooted in sorcery, magic and witchcraft. Many magicians and other occultists have experienced levitation and various forms of supernatural power. These sorcerers typically cast spells or perform other rituals in an attempt to conjure the power to accomplish these feats. It is becoming more and more commonplace to see such expressions of magical performance."

My only response, in my best George Takai voice, is simply "Oh my!"

So, what's this "paranormal event" he's talking about?  A quick YouTube search yielded the following video ad for Pepsi with Dynamo "levitating" alongside a London bus.  I assume this is what Delzell was referring to in his column:


Yes, there are people walking our streets, people who look perfectly normal and hold responsible jobs (like Lutheran pastor and columnist), who believe this little stunt was DONE WITH ASSISTANCE FROM THE PRINCE OF HELL, SATAN HIMSELF!

If you want to have your illusions shattered, read about how this trick (yes, it's a trick) is done.  Of course the true believer will just argue that while some may do these cheap tricks, Dynamo performed a secret ceremonial rite to sell his soul to Satan for the chance to star in a Pepsi commercial.

Wave at Saturn today

Today, Friday, July 19, between 2127 and 2142 UTC (5:27-5:42 EDT), the Cassini spacecraft will be taking pictures of Saturn.  It has been doing that for almost a decade now (since it arrived in 2004) but what makes these pictures special, however, is that the pale blue dot of Earth - our home - will be visible as well.

It's been done before.  I've used the image below, taken by Cassini in 2006, when I teach Solar System Astronomy showing Earth just above the rings of Saturn (but almost a billion miles away).  It's the pale blue dot first made famous by the late astronomer Carl Sagan back in 1994 from Voyager spacecraft images.  All humans who've ever existed were born and died on that little blue dot.

The Cassini Imaging Team Leader Carolyn Porco has organized an event called The Day the Earth Smiled and is urging everyone to go outside when Cassini is imaging Earth and smile, wave, raise a glass, whatever to Saturn.  Really, to ourselves, as humans, for having the ability to take a group picture from a billion miles away.

At 5:30 pm, here in the Hudson Valley, Saturn will be out (but not visible since it's daylight).  It will be about 30 degrees above the horizon in the southeastern sky (148° azimuth).  It will also be some 900 million miles away from us.  The image below shows the positions of Earth and Saturn in the solar system today.

Can you see why Saturn is in the southeastern sky in the evening?  Below is a simplified view of the orientation of the Sun, Earth, and Saturn (not to size or distance scale).

The half of the Earth facing the Sun is illuminated in daylight and the half facing away is dark nighttime.  From above the North Pole, the Earth is rotating counter-clockwise.  Our position on Earth in late afternoon (5:30 pm) is shown with the red arrow.  It's still daylight (we can see the Sun) but we can also see Saturn rising in the east (theoretically, can't really see it because the sunlight washes out the dimmer light of the stars and planets).

So today at 5:30 this evening, here in the Hudson Valley, go outside, face the southeast, and smile at Saturn.  I'll post the picture from NASA as soon as it's released (and take a picture of myself waving to Saturn from Earth).

Cancer - tumors and crabs

Another post on geologist Steve's weird mental meanderings.

Have you ever wondered why cancer is called cancer?  Cancer is a nasty disease (really a group of diseases) but also an astronomical constellation (and astrological sign of a crab).  What the hell do those have to do with each other?

The ancient Babylonians were excellent naked-eye astronomers and observed the path of the Sun and planets through the sky over the course of the year.  This is the ecliptic which they divided into 12 regions, each marked by a specific constellation (called the zodiacal constellations).

 

Cancer the crab is one of those constellations.  Why is this upside-down "Y" pattern named after a crab?  Who knows.  All we can say is that some time prior to 1,000 BCE, a Sumerian in the Tigris-Euphrates Valley believed it looked like a crab and called it al-lul (alluttu in Akkadian).

 

 

When Babylonian texts came into ancient Greece, the constellation was called καρκῖνος (karkinos), the greek word for crab.  Cancer in English.

 

OK, so why do we now use the term cancer in medicine?  What's it have to do with crabs?

 

Blame the ancient Greek physician Hippocrates (c. 460 BCE – c. 370 BCE). Cancer as a disease has been around as long as man and Hippocrates was very familiar with its end-stage manifestations.  No one's quite sure why he used the term καρκῖνος or crab to describe malignant tumors (carcinomas) but a number of theories have been proposed.  Some say it's named for the hardness of some malignant tumors (like a crab's carapace).  Others claim the name is from the fact that tumors can spread tendrils throughout the body (like a crab's legs).  Or maybe it's due to the sharp pain and difficulty in eradicating it from the body (like a crab's tenacious and painful pincers).  Who knows?  The term stuck, however, and Greeks following Hippocrates continued to use the term.

Whatever the etymology, it's a word and a diagnoses that no one ever wants to hear.

Cute little crustacean has a bad rap!

Interviewing for community college teaching

I've been teaching geosciences at either a college or university full-time for 16 years now (14 of them at my present-day community college position).  This doesn't include years spent teaching various labs as a graduate teaching assistant at two different state universities.  I've also been a department chair for several years and have served on and chaired numerous faculty search committees in a number of different academic areas and will continue to do so in the future.

Let your good buddy Steve tell you how not to apply and interview for a full-time community college faculty position.

First a disclaimer (because some people are dopes) - I speak for no one but myself.  Not my employer.  Not community colleges in general.  Not my faculty colleagues.  Not anyone.  Just me giving you some free advice (and you know what that's worth).  Take it as guidance from a kindly uncle - a voice of experience hoping to save people some embarrassment and wasted time (especially my wasted time).

First, a few generalities...

1. Understand the difference between adjunct and full-time faculty.  Adjuncts are people hired to teach one or two courses a semester as needed (they are contractually not allowed to teach more).  They are not well paid and have no benefits.  While we try to hire adjuncts who are qualified (and many in our department have PhDs and years of teaching experience), we'll also hire people who are promising with a bit less academic and/or teaching experience (but still hold them to high standards).  Feel free to send a resume to me inquiring about adjunct positions - they come and go over the years so we're always looking for good instructors.

2. Full-time faculty, however, are not hired off the street.  Sending an inquiry, resume, CV to the department chair asking about a full-time position in your field that was not advertised is a complete waste of time.  I might call and say we have one class available for an adjunct but I will never call and say "Oh yes, we just happened to be looking for a tenure-track physics professor.  It's so lucky your resume just arrived!"  Never.

3. Positions don't open up all that often.  We have to sometimes fight to even get retiring or resigning professors replaced by a full-time position (due to poor financial support of community colleges by both the state and county legislatures, budget lines are always up for slashing).  It's a several month-long drawn-out process to hire a full-time, tenure-track faculty member.  We only have a few dozen full-time faculty members at our institution (the other 2/3 are adjuncts) and we all love our work - it's rare for people to leave and for jobs to open up (one or two a year in the whole institution on average).

4.  Given the above, we're picky about who we hire.  A bad hire will haunt us for years and cause a lot of wasted time, effort, and aggravation.  We might have to work with you for decades - we obviously don't want to hire an incompetent, an asshole, or a slacker.

Now let's talk about the application process.  You see an ad (maybe online in the Chronicle of Higher Education) and want to apply...

1. Make sure you at least mostly fit the job ad.  Most of our ads are a bit generic (because community college instructors are generalists - we don't look for instructors of British literature, we look for instructors of English - you'll teach a few sections of Freshman 101 and may a section of Brit Lit once a year if you're lucky).  We've had people apply who aren't even close (one I remember is a retired attorney with zero teaching experience or background who thought it would be fun to teach Earth science - it's insulting he thought it would be so easy).

2. Send a professional-looking resume - or, better yet, a curriculum vitae (CV) like a real academic.  Bad grammar, bizarre formatting choices, and spelling errors make me want to crumple it up and toss it.  Search committees reject applicants for interviews for such things all the time.  This is especially necessary for applicants whose first language is not English - have a native English speaker proofread it (pay someone $50 to do it if you don't have literate American friends).  No one's saying we'll toss an applicant for a misplaced comma or a simple typo but you wouldn't believe some of the shit people send.

3. Include all of the material asked for in the ad.  If the committee wants a statement of teaching philosophy, write one up (if you're applying at a community college, make sure it references teaching at a community college).  If we want a list of references, get one together (be sure to tell them in case we decide to call!).

4. Don't include lots of extra crap.  I don't care if you worked at McDonalds for 3 months in 2005 (we all worked crappy jobs in college to have some beer money, so what).  Don't tell me you are listed in Who's Who (once they started sending me those emails, I knew it was a scam).  Don't list some bullshit certificate in JavaScript you got from taking an online class.  Don't tell me your hobby is knitting or church bingo or collecting 50's pornography.  I don't care.  Oh, and since we're a community college, don't tell us about all the wonderful research you want to do (good luck with a 15-contact-hour/semester load and possible summer classes).  What I do want to know is your contact information, where you went to school and when you received your degrees, and relevant job information (like teaching!).  I also want to know that you understand community colleges.

5. Be patient.  It takes a while to get a search committee together, read applicant's materials, decide who to interview, sometimes even go to a second round of interviews, etc.  I know that sucks if you're waiting, but that's just the way it is.  When I chair search committees, I do try to let everyone know we received their material and the eventual outcome.  Unfortunately, a lot of schools don't.  But don't make a pest of yourself and start calling - I'll just let it go to forever unanswered voice mail.

If you get called for an interview...

1. Be appropriately dressed.  I'm a geologist and I dress pretty piss poor some days when I'm in the lab or going out in the field.  In the summer, I'll come to my office in a tee-shirt, sandals, and shorts.  But it's a fucking interview.  Business casual is good, no need for a three-piece suit, but don't show up like a slob (yes, people have).

2. We're not out to get you, we want you to be the one we hire.  If we bring you in for an interview, you're qualified for the job.  I know it's hard, but relax and have fun with it.  Our interview questions are pretty straightforward - it's amazing how many people flub "Why do you want this job?"

3. Answer the questions honestly.  We ask questions during the interview that have no "correct" answer.  "A student comes the last week of the semester, is failing the course, and asks what he can do to pass.  What do you tell them?"  Some of us on the search committee might tell the student to register for the course next semester because they're out of luck and will fail.  Some might give the student some opportunity to hand in late work for more credit.  Some might let weight the final exam a bit more so they could pass if they did well on the final.  We want to see how you go about answering the question, not what you'll actually do with this hypothetical student.  We don't care - you'll have the academic freedom to do different things depending upon your teaching style, syllabus, college policies, etc. (unless your answer is to offer the student an A for $100).

4. Community colleges are teaching institutions.  Some people look down on us.  They're assholes.  If we catch a whiff of you implying that you're "settling" by deigning to work for us, you've lost the job.  If your primary goal is to do research, chase grants, write papers, work with brilliant students, have assistants to grade papers, don't apply to a community college.  If you want the challenge of teaching 100- and 200-level classes in your broad subject area to students at an open-admissions institution, then we are where you should be teaching.  At many community college, you will teach 15 contact hours each semester (5 three-credit classes).  It doesn't leave a lot of time for things like research or publication.

5. The most important part of the interview is the teaching demonstration.  We always ask applicants for full-time positions to teach for 15-20 minutes on an assigned topic.  We know that you know the material (unless you lied on your resume).  We want to see how well you can communicate that to a class of 20-30 students who don't know it.  A lot of applicants lose the job by not doing well on the teaching demo.  You're not impressing us with your brilliance, you causing us to think the students will have no idea what the fuck you're talking about.  A good teaching demo is prepared and rehearsed (don't read off a sheet of paper!).  It has a logical flow and makes sense.  A little nervousness is excused, being completely rattled is not.

6. Understand the job.  We don't pay well - if you want high pay, find another job.  It's not only teaching.  Faculty are expected to advise and mentor students, serve on committees, engage in professional development (especially in my field - the sciences), perform curriculum development and assessment, etc.  If you imply you just want to teach and leave, we'll wonder who the hell is going to do all the extra work and then we'll realize it's us!  Not good.

Just a few thoughts off the top of my head.  Like I said, most of our faculty (once they survive the first couple of years and show they can cut it) love it here.  They stay for a long time.  I'm starting my 17th year of full-time college teaching this August and looking forward to the start of classes.  I love standing in front of a group of freshman and talking about geology!  There's nothing I'd rather be doing.

Strained by stress

Yesterday, I posted about stress (σ = F/A) in geology.  Today, I'll talk a bit about strain.

Strain, abbreviated by the lower-case Greek letter epsilon (ε), refers to the change in a body from some original configuration to a new configuration.  So what's that mean?  There are different ways something can strain - imagine a cube of rock acted upon in various ways by some outside forces.

Translation - The cube can be shifted, without changing it in any other way, from one place to another.

Rotation - The cube can stay in place but be rotated a specified number of degrees about some specified axis or axes.

Dilation - The cube can change its size (volume) while still remaining in the same place as a cube.

Distortion - The cube can be sheared to change its shape while maintaining a constant volume.

The cube can also be subjected to two or more of these changes in various different ways resulting in a very different object from what you started with in the original configuration.

You can, of course, treat this all mathematically and it gets complicated pretty quickly.

Let's look at some real-life examples. Below is a picture of a lettuce field in El Centro, California.  Note how the background has translated to the left compared to the foreground.  That shifting was caused by movement along the obvious fault seen on the surface here.

Below are rotated minerals within a sheared rock.

Below is an example of dilation.  The granite which makes up Mount Rushmore formed kilometers below the surface where it was under a lot more confining pressure.  As it eroded to the surface, over geologic time spans, it expanded a bit in all directions forming fractures (called unloading joints by geologists). By doing so, this large block of rock increased its volume.

Below is the fossil of a trilobite that has been distorted. As the soft sediment it was buried in was compressed and lithified (turned to stone), it stretched out horizontally deforming its original shape.

These are all examples of strain in rocks.

So, how do you get a rock to strain?  You apply stress to it - the more stress applied, the greater the resultant strain.  Below are two examples, one with layers of turkey and cheddar cheese and the other with real rock strata.  In both cases, these layers were subjected to a horizontal compressive stress.

Turkey & cheddar fold

 

Folded rock layers

 

Not surprisingly, the amount of strain in the rock is proportional to the stress it was subjected to during deformation.  In the 17th century, English physicist Robert Hooke (1635-1703) figured this out with some springs and weights.  The heavier the weight, the more extension of the spring (it breaks down at some point as the spring overstretches or breaks).

 

Basically, however, it's a simple linear relationship where the ratio of stress (σ) to strain (ε) is a material contestant called Young's Modulus (E).

   E = (σ / ε) or σ = E ε

 

Young's Modulus can vary greatly among different rocks types (even within a single rock type).  When subjected to geological stresses, a relatively soft layer of marble will behave very differently from a stiff layer of quartzite.

Here's what typically happens with a typical rock when placed in a compressive press, for example.

As you apply stress, the rock strains (deforms).  The more stress, the more strain, in a relatively linear (straight-line) fashion.  This strain is elastic strain and is recoverable.  When the stress is removed, the strain goes away and the rock is unchanged from when it started.  Think of a rubber band.  Apply stress and it stretches.  Release stress and it goes back to it's original shape.

At some point, however, the strain becomes plastic which means it's permanent.  Remove the strain and the rock is permanently deformed into a new shape.  Thick of it like bending a paper clip.  Once you bend it, it's bent.  Eventually, of course, there's so much stressing and straining going on, the rock breaks.

With plastic deformation, you get ductile strain (flow of the material).  Think of folds in rocks.  With rupture you get brittle strain (fracture of the material).  Think of faults in rocks.  With rocks, ductile vs. brittle deformation depends of the geological material (shale, sandstone, granite, etc.), the temperature and pressure at which deformation takes place, the presence of absence of water in the rock, and the strain rate (how fast it's straining - take a piece of chewing gum out of your mouth and pull it slowly apart and then pull it apart fast -see the difference?).

Keep in mind that this is all way oversimplified, however.  Continuum mechanics is a very complex field of study - especially when looking at rocks which are extremely heterogeneous materials, unlike the steel and concrete engineers study.

Stress (geologically-speaking)

Most of us have a lot of stress in our daily lives.  The word "stress" is used in geology too, but in a bit of a different way.  In geology stress is defined as an average force (F) per unit area (A) and is abbreviated by the lower-case Greek letter sigma.  Mathematically it's σ = F/A.

Why is it a force per unit area?  I tell my students to think of it this way.  Imagine a 50 kg woman (110 lbs) standing on your bare foot.  She's wearing those fashionable shoes to the right.  Would you rather she stand on your foot with the stiletto heel or with the flat part of the shoe where her toes are?  Why?  It's all the same force (50 kg).  Well, obviously, the cross sectional area in contact with your foot is important.

 A unit of stress most people are familiar with is pounds per square inch (lbs/in² or psi).  In geology, however, we use the SI unit pascal (Pa) named after the French mathematician Blaise Pascal (1623-1662).  A pascal is a small unit equal to only 1.450377 x 10^-4 psi and is defined as 1 newton (N) of force per square meter (m²) of surface area.  In geology, where we deal with stresses associated with plate tectonics and mountain building, the unit megapascals (MPa or 1,000,000 Pa) is routinely used.

How much stress to crumple up these mountains?

As an aside...  Don't confuse stress with pressure which use the same units.  The atmospheric pressure, for example is 14.7 psi and you might inflate your car tires to 30 psi.  What's the difference between that and someone standing on your foot exerting a stress of 100 lbs/in²?  The difference is that pressure is a scalar (non-directional) quantity and stress is a vector (directional) quantity.  In other words, pressure is the same in all directions (sometimes called a confining stress) while stress is directed.  We represent stress as an arrow - it has a magnitude and a direction.

In geology, we often talk about different kinds of stress.  In the diagrams at left we see examples of tensile stress (a pulling apart), compressive stress (a squeezing), and shear stress (side-to-side movement).  The arrows, of course, denote the force directions.  These types of stresses are what make rocks deform (change size, shape, position, and/or orientation).  By the way, it's not just geology, engineers talk about stresses in concrete pillars and steel I-beams instead of rocks (rocks are actually harder to analyze because they vary so much unlike engineered materials).

Of course it's a bit more complicated in that we're looking at very simple examples and a better analysis is done of stress in a three-dimensional stress field.  In more advanced structural geology (the branch of geology dealing with rock deformation), we talk about the stress ellipsoid where the stress field around a point can be broken down into three principal stress axes (σ₁, σ₂, and σ₃).

By the way, the stress ellipsoid would be a sphere if all directions were equal as in a case of pressure.

Think in terms of large-scale plate tectonic movements.  Tensile stresses are associated with the rifting apart of continents like the modern-day East African Rift Valley, for example.  Compressive stresses are associated with collisional events like India colliding with Asia to crumple up the Himalaya.  Shear stresses are associated with plate boundaries sliding sideways past each other like the San Andreas fault boundary in California separating the North America and Pacific Plates (hypothetical example shown below).

Next time I'll talk about the relationship between stress and strain in geology.

Word of the Day - Botryoidal

Bored so I thought I'd toss up a quick post tonight...

Every fall semester, I teach a laboratory course on Physical Geology and one of the topics, of course, is minerals.  In looking at minerals, students learn a lot of terminology including words to describe a minerals crystal "habit" or shape.

Many of the terms are self-explanatory like cubic, platy, and fibrous.  Others are a bit more exotic including the term botryoidal which is unfamiliar to most students.

The term is derived from two Greek roots - botrus (βότρυς) which refers to a bunch of grapes and eidos (εἶδος) meaning resemblance or likeness.  It's a mineral that grows bulbous masses which (roughly) resemble a bunch of grapes.

A couple of common examples below:

Hematite - Fe₂O₃

Malachite - Cu₂CO₃(OH)₂

 Rhodochrosite - MnCO₃

 

Now you know a word you may not have before.  Go off and impress your friends.

Where are all the videos?

From xkcd webcomic:

The distant Sun

I write this as much of the country is enduring a heat wave with record high temperatures in many places (including here in the Northeast) where every day has been in the mid- to upper-90s and Central Hudson Gas & Electric is cleaning up financially from all the air conditioning.

One common misconception many people have is that it's hotter in the summer because the Earth is closer to the Sun during this time.  As a matter of fact, the exact opposite is true - we're actually near our furthest point from the Sun right now.

Polish mathematician and astronomer Nicolaus Copernicus (1473-1543) is crediting with publishing the first convincing model of a heliocentric solar system (a system where the planets orbit the Sun).  This replaced the old geocentric model (a system where everything orbited a stationary Earth) which dated back to the ancient Greeks and was the model supported by the Catholic Church's interpretation of Scripture at the time (Copernicus' book was placed on the list of books banned by the Church since it taught "heresy").

Notice that Copernicus' model (at right) shows circular orbits.  This was what everyone assumed because circles were "perfect" geometric shapes.  The orbits simply had to be circular.

Johannes Kepler (1571-1630), a German mathematician and astronomer, born a generation after Copernicus died, was playing around with years of observational data gathered on the orbits of planets gathered by Tycho Brahe (1546-1601) when he discovered that the data fit together a lot better if we assume planetary orbits are not circular, but rather elliptical.  From this, Kepler developed his famous three laws of planetary motion showing that planets orbit the Sun in an ellipse with the Sun at one focus of that ellipse.

Here's a nice figure illustrating this.  I've talked about solstices and equinoxes several times in the blog (use the Search box to find the posts) and they're the positions where the Earth's Northern Hemisphere is tilted toward the Sun (June solstice), the Earth's Southern Hemisphere is tilted towards the Sun (December solstice), or the Earth is tilted neither toward nor away from the Sun (equinoxes).

THIS IS THE ONLY REASON WE HAVE SEASONS!

When our hemisphere is tilted toward the Sun around June 21, we get more daylight and the Sun is higher in the sky imparting more incoming solar radiation (insolation) and it's summer.  When our hemisphere is tilted away from the Sun around December 21, we get less daylight and the Sun is lower in the sky with lower insolation and it's winter.  During the equinoxes around March 21 and September 21, we get about equal-length days and nights and medium amounts of insolation and it's spring or fall.

That's also why seasons are reversed south of the equator (as we roast, they're experiencing winter).

Note in the figure above, however, there are also points labeled perihelion and aphelion.  These are the Earth's closest (perihelion) and furthest (aphelion) positions from the Sun in its elliptical orbit.  While the diagram says July 4, this year's aphelion was actually at 1500 UTC (11:00 am EDT) on Friday, July 5 (I'm writing this on Monday the 8th).

The difference between aphelion and perihelion in the Earth's orbit is actually rather small.  According to Wikipedia, the values for the Earth's perihelion and aphelion distances are 147,098,290 km (91,402,640 mi) and 152,098,232 km (94,509,460 mi) respectively.  The average distance is 149,597,870.7 km (92,955,807.3 mi).  This gives us:

   (152,098,232 km - 147,098,290 km) / (149,597,870.7 km) * 100% = 3.34% difference

A 3% difference is distance between aphelion and perihelion is not enough to cause noticeable differences in insolation and so plays no role in our seasons.

So, even though the summer sun feels like it's close to us as it blazes down on our heads (especially if you go to the desert Southwest where it's well over 100° F), it's actually about as far from us as it gets all year!

The Century House Historical Society

Back in May, I was asked to serve on the Board of Trustees for the Century House Historical Society, a local not-for-profit 501(c)(3) organization whose goals are to maintain the Century House and Widow Jane mine on the A.J. Snyder Estate in Rosendale, NY and to preserve the fascinating history of the local Rosendale Cement District.

The Century House (dates to 1809)

I happily accepted since I strongly support their mission as a resident of the Town of Rosendale and as a geology professor with a strong interest in the local geologic history. One of the things I'd like to do over the coming year is delve into the extensive historical archives of the Century House Historical Society.  There's a real story (many stories, actually) to be told regarding the important history of the natural cement industry in this area.

The Widow Jane Mine

So, anyway, I thought I'd post a little about the Society since we can use all the help we can get in preserving and maintaining this local history.  As our website says:

"Everything you see around you: maintenance of over twenty acres, the care of our buildings and collections, and our outstanding educational programs are all accomplished by volunteers. We have no wealthy benefactors but we do have a bank mortgage, insurance costs, and an array of other expenses. Our income is derived from fund raisers, programs, membership dues, and donations."

How can you help?

* Come for a visit or to one of our neat events ("like" The Century House Historical Society on Facebook for notifications of upcoming events).

* Donate money (tax deductible) to help us preserve the history of this unique area. 

* Volunteer to help out.  If money's tight, we can always use volunteer help with maintenance and cleanup of the site.

* Become a member. It’s only $15/year for an individual or $25/year for a family. See the website for more details.

Here are two of our upcoming events in July (more to come in August):

Taiko Masala - Traditional Japanese drumming inside the Widow Jane mine.  Imagine the sounds of powerful drums reverberating off the rock walls of mine, immersing you in their primal sound.  Sunday, July 14, at 3:00 pm.  Tickets are $20 at the door and bring a folding chair.

Taiko Masala from last year's show in the Widow Jane Mine

DaDa Spill - DaDa Spill is a take off on the term data spill that means a breach in security.  This artistic event, on Sunday, July 28 at 3:00 pm, is described as a "multi-media installation, performance and crowd project" that will take place in the cool and vast interior of the Widow Jane Mine.  $10 for adults, kids free.

Museum & Mine - You can also stop by any Sunday (except July 21 when we're closed due to the Rosendale Street Festival) when volunteer docents will be at our small, but interesting, museum and you can walk down and enjoy the cool (even on the hottest summer days) Widow Jane Mine.

I plan to be at both of the above events (and others).  Stop by and say hello!

Fireworks - Chemistry & Physics

It's the fourth of July and everyone loves a good fireworks show.  Lots of chemistry and physics (and even some geology) behind these awe-inspiring shows of hot summer evenings.

To launch of fireworks shell, you first have to light the fuse.  Fuses for fireworks are generally formed from cords with a black powder core.  They burn at a controlled rate and are used to ignite the shell's slow-burning black powder propellant - a combination of 75% saltpeter (potassium nitrate or KNO₃), 15% charcoal (basically C), and 10% sulfur (S).

Black powder has been around a long time and was invented back in 7^th century China.  It's a "low" explosive that burns at slower subsonic speeds rather than the fast detonation of  "high" explosives making it ideal as a propellant.  The charcoal in black powder acts as a fuel, the sulfur increases the rate of combustion by lowering the temperature of ignition of the mixture, and the saltpeter breaks down to provide the oxygen necessary for combustion (4KNO₃ → 2K₂O + 2N₂ +  5O₂).

Professional fireworks are launched out of mortars

unlike bottle rockets which use sticks as shown above

As the shell ascends, a time-delay fuse is still burning toward the upper compartment of the shell where the "stars" are located.  The stars are 3-4 mm clay-like masses which contain the chemicals necessary for the pyrotechnics show when the shell explodes from its charge of high explosives.  It's all a matter of timing.  You want the fireworks to explode at the apex of the shell's climb.

A 6" fireworks shell.  Fuse is at left, black cubes are the "stars",

a gray explosive charge is to the right, and the black powder

propellant is at the far right.  All encased in a cardboard shell.

Setting up the mortars and shells for a show

The high explosive charge ignites the stars and tosses them outward.  The packing of the explosive and the stars determines the type of effect- the spherical peony or chrysanthemum, the expanding ring, the drooping willow, etc.

 

There's a whole art and science behind the packing of fireworks shells with different configurations, formulations, and shapes.

 

Colors, of course, are due to the chemical composition of the stars.  Reds are formed from strontium (SrCO₃) or lithium carbonates (Li₂CO₃), orange from calcium chloride (CaCl₂), yellow from sodium chloride (NaCl), green from barium chloride (BaCl₂), blue from copper chloride (CuCl), etc.  Every manufacturer has their own secret formulations.

The explosive boom heard when watching a fireworks display is caused by the high explosive charge pushing air outward at faster than the speed of sound (340 m/s) causing a sonic boom. There is a noticeable delay between seeing the explosion and hearing the explosion since light travels much faster at 300,000,000 m/s (almost a million times faster!).  There's a 3 second delay between the flash and the boom for every kilometer of distance you are from the exploding shell.

Another funny thing about fireworks is that they appear to be two-dimensional, like they're being displayed on a flat screen, unless you're right underneath them.  This is because your eyes and brain can't determine which way the burning fragments of stars are moving since they're so bright against a black background.

You've seen the chemistry and physics, where does the geology come in?  Over 2/3 of the world's strontium, for example, comes from China where the strontium sulfate (SrSO₄) mineral celestine, also known as celestite, is mined.  Barium comes from the barium sulfate (BaSO₄) mineral barite.  Lithium comes from minerals like spodumene, a lithium aluminum silicate - LiAl(SiO₃)₂.  People tend to forget that virtually all the chemical elements we use in our modern industrial society have, as their origin, minerals dug from the Earth.

Science, as always, enhances our appreciation of beauty by giving us a deeper understanding of what we see and experience and how everything is connected in the world around us.

Enjoy the show and Happy Independence Day 2013!