Thursday, June 30, 2011

The East Coast rift zone

Yesterday I talked about the Nabro volcano erupting in Eritrea.  Believe it or not, this does have something to do with our own Hudson Valley.

Some 250 million years ago, what's now the northeastern coast of the U.S. was attached to northwestern Africa when the landmasses were basically all together as a supercontinent called Pangaea.

Starting in the Late Triassic Period, around 225 million years ago, Pangaea began rifting apart.

Breakup of North America & Africa from Triassic into Jurassic Periods
245, 210, 180, & 150 million years ago (Ron Blakey, NAU Geology)

Continents rift apart due to the formation of tensile stresses in the lithosphere, typically due to the formation of mantle plumes, which then stretch the crust.  The crust accomodates by thinning and faulting, dropping down linear rift valleys.  The thinner crust results in partial melting of the mantle which forms magma which rises to erupt on the floor of the valley.

As you can see in the series of paleogeographic reconstructions of the breakup of Pangaea, the process began by the formation of a series of parallel rift valleys.  This is the stage the East African Rift system is in right now where Nabro volcano is erupting.

The next step in the stage is linking up of some of the rift valleys to fracture the continental crust.  The area sinks low enough that seawater floods in forming a linear sea.  Look at the Red Sea at left.  That was once a rift valley between the Arabian Peninsula and Africa that completely broke through into a linear sea.  This will someday happen on the African mainland separating the Horn of Africa.

Here in the Northeast, there are a number of failed rift valleys that got left behind when Pangaea finally broke apart (similarly, when the Horn of Africa breaks off, it will be along either the eastern or western arm of the East African Rift and the other will be left as a failed rift).

In the lower Hudson Valley of New York, we have a geologic province called the Newark Rift which extends up from New Jersey into Rockland County (south of the Hudson Highlands and west of the Hudson River).

The Newark Rift was one of those failed rift valleys but during the Triassic Period, when small meat-eating bipedal dinosaurs like Coelophysis were running around, it was an active place of earthquakes and eruptions of lava flows.  Just like eastern Africa today (sans dinosaurs).

Wednesday, June 29, 2011

Nabro Volcano, Eritrea

Shortly after midnight local time, on June 13, Nabro volcano in Eritrea began erupting after a series of earthquakes in the region.  Eritrea, for those unfamiliar with the name, is a country in the Horn of Africa bordered primarily by the Sudan to the northwest, Ethiopia to the southwest, and a long coastline with the Red Sea to the east.

Nabro volcano is located next to the border with Ethiopia in the Danakil depression, shown on the map at right.  This area is also known as the Afar triangle.  It's basically the northern end of the East African Rift Valley which extends down through Ethiopia into Kenya and Tanzania (a western arm of the rift also runs down through Uganda and into Lake Tanganyika between Tanzania and the Democratic (hah) Republic of Congo.

The East African Rift system is where the Horn of Africa (Somalian subplate) is trying to pull apart from the rest of the African continent (Nubian subplate) due to tensile forces in the lithosphere.

These tensile forces lead to faulting which acts to accomodate stretching of the crust by the formation of deep rift valleys.  Periodic movement on these faults results in numerous regional earthquakes.  The thinner crust also leads to melting in the underlying mantle resulting in volcano formation in the rift valleys.

Red triangles on the map are volcanoes (Erta Ale is in Ethiopia near Nabro).

Here's what Nabro volcano looks like from Google Earth satellite imagery.  You're looking southwest over the volcano into Ethiopia (yellow line is border between Eritrea and Ethiopia).  There are no good surface photos of the volcano - it's located in a very arid, isolated, and dangerous region of Africa.

Nabro (13° 22' N, 041° 42' E) is, at 2,218 m (7,277 ft), the highest of the stratovolcanoes in the Danakil depression and belongs to a group of calderas called the Bidu volcanic complex.  Nabro itself consists of two nested calderas (8 and 5 km in diameter) breached on the southwestern side (as seen in the image above and at left).

While it's certainly erupted numerous times in the past, this is the first eruption in recorded history for the volcano.  Below is an image from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite (supporting NASA has practical benefits - we can monitor volcanoes in obscure parts of the world in real-time).

Here's another great image from the Advanced Land Imager (ALI) on NASA's Earth Observing-1 satellite on June 24.

The image is actually false color with infrared.  The red and orange areas obviously indicate high temperatures and show a lava flow extending off to the northwest from the erupting volcano.  The blue white clouds are primarily water vapor and carbon dioxide gas mixed with ash.

This ash cloud has disrupted flights in East Africa and has caused problems for people in the area.

Empathy? What the hell is that?

Just as an addendum to my Asperger's post a couple of days ago...

I recently saw a link to an Empathy Quotient test at Massimo Pigliucci's Rationally Speaking blog.  Go take the test, it's only 60 questions.

Holy shit, I can't believe how low I scored.  My wife scored 45, which is close to average for women (47).  Most men score around 42.  Most people with Asperger's Syndrome score around 20.  I took 'the test twice, the first time by myself and the second time a few days later with my wife of 18+ years looking over my shoulder and "correcting" my answers.

My two scores were 16 and 13 respectively.  That's really depressing and now my wife mocks me about my supposed "lack of empathy."  No wonder I decided to study rocks in college.

Tuesday, June 28, 2011

Peekskill Meteorite

You may not have known it, but yesterday (Monday, June 27, 17:00 UTC) a 10 meter diameter asteroid called 2011 MD passed within 12,400 km (7430 miles) of the Earth's surface.  For reference, that's about one Earth diameter away from us and about 31 times closer than the Moon.  There was no danger of it hitting but sometimes the Earth's gravitational field happens to catch one of these space rocks.  Here's the story of a much smaller meteorite which came crashing into the Hudson Valley 20 years ago.

On October 9, 1992, a meteorite entered Earth’s atmosphere somewhere over Kentucky, exploded into fragments, which continued over West Virginia, where it was first filmed at 11:48 pm.  The trajectory was toward the northeast, moving as a fireball through the skies over Maryland, eastern Pennsylvania, and finally crashing down to Earth striking a 1989 Chevy Malibu belonging to a Michelle Knapp at 207 Wells Street in Peekskill - a town in the in the lower Hudson Valley of New York (across the river from Bear Mountain).

At least 16 people in several states were able to film the meteorite fragments flying through the sky that evening.  The Peekskill fragment was the only one found, but there were others that didn't make such a conspicuous touchdown.

Check out this French website with all 16 known Peekskill meteorite videos.

Here's a picture of the 12.4 kg (27 lbs) meteorite after it struck the car (notice the red paint!).

From  R.A. Langheinrich Meteorites

The meteorite was sliced up for sale to collectors.  Here's one piece that was sold.

The meteorite was classified as an H6 chondrite - a rather ordinary meteorite that wouldn't have commanded such a high price without its amazing history.  Meteorites are traditionally classified as either iron, stony-iron, or stony.  Chondrites are a type of stony meteorite characterized by spherical chondrules which are believed to have originated as millimeter-scale molten droplets of silicate minerals (olivines and pyroxenes) freely floating in the early solar system.  The dust, small grains, and chondrules that make up the small asteroid parent body sources of these meteorites represent some of the earliest material from our forming solar system some 4.56 billion years ago.

Chondrites make up 86% of the witnessed meteorite falls, they're very common.  H-type chondrites are so-named because they have the highest total iron content (~30%) of the stony chondrites.  The 6 refers to the petrologic class of the meteorite - basically the amount of thermal metamorphism it experienced.  We may even know where all H-type chondrites come from, there's good evidence that collisions with an asteroid called 6-Hebe provided the raw material for these rocks.

The wealth of observational data allowed the velocity and orbital characteristics of this meteorite to be calculated.  It's pre-atmospheric velocity was estimated to be 14.72 km/s (almost 33,000 mi/hr!).  Prior to colliding with the Earth, its elliptical orbit around the Sun would have had a perihelion (closest approach to the Sun) of 0.886 AU and an aphelion (furthest distance from the Sun) of 2.1 AU (1.0 AU, or Astronomical Units, is the average distance of the Earth to the Sun - about 150 million kilometers or 93 million miles).

So, while having a meteorite strike your car may sound like a bad thing, it's actually like winning the lottery.  The car and meteorite were purchased at auction from Ms Knapp for about $100,000 (back in 1992) and have toured the world.  Here's a picture of the famous car and meteorite on display in a glass box (hence the reflections) in Paris.

A meteorite is welcome to strike the back of my car any time.

Monday, June 27, 2011

Proud homeschooling parent

My two children, a boy and a girl, are both 10 years old (fraternal twins) and just finished 4th grade.  They're homeschooled so we don't exactly follow the New York State curriculum (shhh, don't tell the district superintendent) and only use a formal curriculum for mathematics (Saxon).

Since we like to have a general idea of how they're doing, we do give them standardized tests at the end of the year (but we don't "teach to the test" in any way) and they recently had the California Achievement Test (CAT) from Seton Testing - a nationally normed standardized test.

My daughter had an overal composite percentile score of 97 and my son's was 96.  The only section not in the 90's for my son was Language Mechanics at 80th percentile and the only section not in the 90's for my daughter was Comprehension at 67th percentile (personally, I think she rushed through it or something because she does nothing but read at home and I'm sure her comprehension is better than that).

And here's the difference between public schooled kids and homeschooled kids.  In public school, my kids would just move on to the 5th grade.  In homeschooling, my wife and I look at these scores and say Emily, you have to work more on comprehension and Lucas, you have to work more on grammar.  The education is tailor made to both the kid's strengths (what do you want to study?) and weaknesses (what do we need to work on?).  No one gets left behind and no one advances until we know they truly understand the material.

It's not for everyone but so far has been working well for us.

Thursday, June 23, 2011

Asperger's! Really?

This is a bit of a personal post, so if you're looking for interesting geology, come back tomorrow.

My ten-year-old son has displayed some Asperger's-like symptoms in the past that have concerned his mother and me.  Even a pediatrician we saw when his regular doctor was unavailable wondered, out of the blue with no mention of it from us (he was in for being sick), if he might be somewhere on the autism spectrum.  So, we ended up taking him to a pediatric neurologist expert for a consult; she talked to him for a while and said she didn't think there was anything to worry about. Since we homeschool anyway, it's not too big a deal in his day-to-day life (I do think that if he went to public school, however, he'd be a target for bullies as I was at his age).  So, we're taking her expert advice and not worrying about it for now.

Anyway, there are these screening tests you can take (for adults or children) to see if you might have Asperger's Syndrome.  My son, at least when me wife and I fill out the test for him, seems to score pretty high.  I also score amazingly high as well (my wife, a paragon of normality, does not).

A typical screening test for Asperger's is the AQ (Autism-Spectrum Quotient) test developed by psychologist Simon Baron-Cohen and colleagues at Cambridge's Autism Research Centre (here's one online version you can take).  It has 50 statements that you either have to definitely agree, slightly agree, slightly disagree, or definitely disagree with.  The average score in the control group was around 16.5 while 80% of those with autism (or a related disorder) scored above 32.  I score between 37-40.  I took it more than once on different days, hence the spread in scores and when my wife took it for me, she also came up with a comparable score.

Well, I obviously don't have autism but I definitely have some of the characteristics of Asperger's Syndrome.  As a child, I was shy, liked to read, and was curious about everything (my mother tells me they nicknamed me "the little professor" when I was young).  I much preferred talking with adults rather than with kids my own age and didn't have many friends.  Never liked loud abrupt noises (even today) or changes in my routine.  In school, I was frequently targeted by bullies. As a tween, I was very into electronics and taught myself basic DC/AC circuit theory, how to read schematics, and built a number of electronic devices (if computers had been around then, I'm sure I would have been into them).

As a teenager, my social awkwardness peaked, never had a girlfriend, almost no friends (usually other socially awkward geeky males), and spent much of my time skipping school and reading books or walking alone in the woods.  School did nothing for me other than threaten me and my parents for my bad attendance (if I ever ran into one of those teachers today, I'd be hard pressed not to kick the shit out of him since he was such an asshole to me - but I digress!).

So I ended up dropping out of high school at 16 (I really stopped attending when 15).  Not because I couldn't handle the work, I've taken proctored IQ tests and easily qualified for Mensa, but because I hated the environment so much.  I mostly stopped being bullied because I grew larger when I hit puberty (adults always asked me if I played football) but I really couldn't stand the other kids my age.

So, I eventually went to work, started hanging out with people several years older than me, learned to drink beer (and other things) but still never really connected well with people - especially girls.  Started going to community college (which is why I'm such a big supporter of the community college mission) and, after a number of years, transferred to a four-year school, got my degree and went on to graduate school (the process was not a smooth one, I couldn't attend college every semester because there were some times I had no money to pay for it).

Even though I despised middle and high school, I loved college.  Hell, I'd go back to school now and study something else if I could!  Still mostly a loner, most of my friends were computer geek types (by then I was heavily into computers and knew several programming languages).  Shameful for me to admit, my first real girlfriend wasn't until graduate school.  The bad thing about social awkwardness, whatever its reason, is that it does tend to turn males into misogynists - especially when you're a lonely, but painfully shy nice guy and women you like are dating complete douchebags and complaining that there are no good men out there (but I digress again).

So, long story short, I'm still socially awkward, don't really have any close friends, and spend an awful lot of time reading (nonfiction primarily) or walking in the woods by myself as I did as a kid.  I pursue lots of eclectic interests and feel I have little in common with most people.  I've learned to compensate though, get married, and fool a lot of people into thinking I'm "normal" (of course, now I've just blown my cover).  I never thought about it as a "syndrome" just the way I am (fucked up).  I certainly don't have all the symptoms of Asperger's Syndrome, and self-diagnosing from an online test is foolish (although I think my wife really believes I have Asperger's).  Bottom line is that I don't really give a shit at this point in my life.

So why share all of this?  No idea.  I find it interesting to think about and it's my blog and I write about things that interest me.  So, if you find yourself talking to me some day and the conversation seems awkward, it's not because I don't like you or am bored, it's because the wiring in my brain is likely fucked up.  Or maybe I don't like you and am really bored out of my mind with your incessant chattering.  Who's to say?

Wednesday, June 22, 2011

Top 10 College Majors that Pay

Lord knows I don't believe money is the most important thing in life given that I teach at a NYS community college, but if that's your thing, here's what you should major in according to

This is for graduates with a bachelor's degree and either starting median pay (darker blue bars) or mid-career median pay (lighter blue bars).  See website for methodology.

Note that 7 of the 10 fields have "Engineering" in the job title and all are heavily math dependent.

What's ironic about this is that our community college offers an engineering major that's always on the verge of being discontinued due to low enrollment.  Our students do very well, often transferring to schools like Clarkson and RPI, but the real problem is that virtually all of our incoming students (local high school graduates) are so deficient in math skills it would take them 1-2 years before getting up to calculus I level math such that they could even start taking engineering classes!

We have plenty of humanities and social science majors, however.  I wish them luck finding employment in today's marketplace.

Tuesday, June 21, 2011

Happy Solstice

In honor of the solstice, I took a short hike this afternoon to the Shawangunk Ridge near the Trapps off Route 44/55, lay down, rested my head on my pack, and enjoyed the warm breezes and a few raindrops.  Nothing more to say today...

Monday, June 20, 2011

Upheaval Dome, Canyonlands National Park

I finally got around to stitching together 7 photographs I took while standing on the rim of Upheaval Dome in Canyonlands National Park last summer.  I used Hugin, a great free panorama photo stitcher.  (Click here for a full-sized image)

Upheaval Dome is an odd feature that stands out like a sore thumb when viewing the Canyonlands area from above.  Here's what it looks like from satellite imagery in Google Earth (38° 26' 05" N, 109° 57' 05" W):

So, when a geologist sees a feature like this, they wonder how it formed.  There are generally only three things that can cause circular features like this - a meteorite impact, volcanism, or an intrusion of magma or salt.  So which was it?

Well, we can rule out volcanism.  In this area of the Colorado Plateau, the only rocks are flat-lying sedimentary strata and there are no traces of any volcanic rocks in or around Upheaval Dome.  Here's an example of the layer-cake geology of Canyonlands from a hiking trail near Grand View Point.

For years, the two competing hypotheses for the formation of Upheaval Dome were the intrusion of a salt diapir (a magma intrusion is ruled out for the same reason as volcanism) or a meteorite impact.  Let's look at each in turn.

The diagram above illustrates how a salt intrusion could have formed this feature. Back in the Pennsylvanian Period of geologic time, some 310 million years ago, the area was flooded with seawater and formed what we today call the Paradox Basin (PaB in image at left below).

Ron Blakey, NAU Geology,

Tectonic activity forming the ancestral Rockies pushed up highlands on the edge of the basin trapping the seawater.  North America was straddling the equator back then and the climate was hot and arid in the region we now call Utah.  Large amounts of seawater evaporated leaving behind thick layers of evaporite minerals like halite (salt - NaCl) and gypsum.

Northeast of the basin, the rising Uncompahgre Uplift was eroding and sediments washed down into the basin eventually filling in the sea and covering the salt with thick layers of clastic sedimentary rocks (clastic rocks are sedimentary rocks formed from sediments - e.g. sandstone).

The pressure from thousands of feet of overlying sediments causes the underlying salt to become plastic and flow.  Being less dense than the ovelying material, it tends to form a plug (diapir) which pushed upward, warping and deforming the overlying flat-lying strata.

Lots of erosion then excavated deeply into this structure forming the feature we see today (click on image below to enlarge).

Harris, et al. 2004. Geology of National Parks. Kendall Hunt

The competing hypothesis is illustrated below:

In this scenario, the strata are flat-lying, the salt deposits beneath have not mobilized or substantially deformed the overlying material, and one day, sometime after the Jurassic Period a meteorite came crashing down.  The meteorite formed a large impact crater, deformed the flat-lying sedimentary strata, and was then deeply eroded to its present-day shape.

So, how do you tell the difference between these two competing stories?  It's a national park so you can't just drill down into the structure to see.  The National Park Service website doesn't take a position, just presents both ideas.  The textbook I use for my Geology of the National Parks course favors the salt intrusion hypothesis.  I believe that the evidence, however, favors the impact hypothesis today.

In Geology of the Upheaval Dome Impact Structure, Southeast Utah, (Kriens, Shoemaker, & Herkenhoff, 1999, Journal of Geophysical Research - Planets, 104), the results of fieldwork in the area presented some good evidence that Upheaval Dome was, in fact, an impact structure even though most geologists at the time favored the salt intrusion hypothesis.  Some of their evidence included:

1.  A deposit of what they interpret to be impactites - partially melted rocks formed from meteorite impact.

2. Shatter cones (conical fracture features formed by meteorite impact) in the Moenkopi Formation.

3.  Seismic refraction work indicated the salt horizon is at least 500 meters below the structure, too deep.

4.  Folds, faults, and clastic dikes around the structure are consistent with an impact origin.

The kicker came in 2008 when Buchner and Kenkmann published in Geology their discovery of shocked quartz grains from the Kayenta Sandstone.  Shocked quartz is quartz that has been subjected to a shock wave - generally from either a meteorite impact or nuclear detonation.  The shock waves from these events deform the crystalline lattice of the quartz crystals and this can easily be seen when examining the mineral under a microscope using polarized light. 

This feature, which can best be seen from space, formed from space.  A bad day for the dinosaurs when a several hundred meter diameter meteorite came crashing down!

Upheaval Dome from the International Space Station, 2007

Sunday, June 19, 2011

Idle Parenting

Interesting concept...  Read this old article from The Telegraph on idle parenting.  Since my wife and I homeschool our children, we actual are a bit like this, but my Protestant work ethic keeps me from being too much of a loafer.  Tom Hodgkinson also has an interesting blog called The Idler.

Saturday, June 18, 2011

Vancouver riots

Not related to science or education, the two things I normally write about, but I have to comment about some horrifying pictures I saw online the other day.  They were images of the rioters in Vancouver after the loss of the Canucks.  View them here.

I convinced this could have, and has, happened in most cities here in the U.S. as well.  Looking at these images, I can't help think of events like Kristallnacht (I'd bet serious money that almost none of these rioters could even tell you what Kristallnacht was).  While 1938 may seem like ancient history to these morons in Vancouver, it was only 73 years ago.  There are plenty of people today who were alive then (albeit small children).

With the right charismatic leader, and worsening economic conditions, we could easily channel the anger of these stupid, ignorant young men and women into attacking and killing jews, or mexicans, or muslims, or gays.  Why not, given what they'll do over a stupid hocky game?  We haven't changed all that much in just a few decades.  Ethnic cleansing and genocide still happen today and those who carry it out are little different from us.

By the way, if I recognized anyone in those photos, even my own child, I would call the police and turn them in.  I would hope other good people will do the same.

Friday, June 17, 2011

Geomythology - Part III

Today I wanted to talk about another aspect of geomythology (see Part I and Part II here).  Here are some more examples of "A geologic feature or phenomenon which has inspired a folklore explanation."

Adrienne Mayor is a researcher who has published a lot on "folk science", the intersection between science and folklore - specifically how some pre-scientific cultures have interpreted fossils. Two interesting books she has written are The First Fossil Hunters: Paleontology in Greek and Roman Times and  Fossil Legends of the First Americans.

Imagine you lived a few thousand years ago farming in what's now China and found something similar to the following fossils:

Might you not imagine the following animal?

This is a picture of me about 10 years ago next to some mastodon bones found in Hyde Park, NY.

What might you think if you found a giant femur (thigh bone) like this thousands of years ago?  Would it be unreasonable to think it belonged to a giant?

Some have even speculated that Pleistocene pygmy elephant skulls, like those found in places like Sicily, may have inspired legends of cyclopes due to the large hole in front of the skull where the trunk attached.

Might a protoceratops fossil have inspired the legendary griffin?

Interesting to speculate about, probably impossible to show conclusively.

Thursday, June 16, 2011

Geomythology - Part II

Yesterday, I talked a bit about the first two of the following three categories of geomythology:

1. A garbled explanation of some actual geologic event, usually a natural catastrophe
2. A geologic feature or phenomenon which has inspired a folklore explanation
3. An association between a mythic figure or object and a geologic feature or phenomenon

Today, I want to cover the third item on the list.

But first some background... Our college participates in a one-book/one-college program where a committee chooses a book each semester and everyone's supposed to read it.  This culminates with a week-long series of presentations (mostly by faculty at the college) on the book and relating it to their various fields.

Last spring the book was Grimm's Fairy Tales and that's what got me to thinking about geomythology because that's basically what I presented a talk about (I was also asked to present it at a Phi Theta Kappa ceremony).  One connection between geology and Grimm's that I found interesting had to do with dwarves.

As a side note, when reading Grimms I frequently stopped after reading a particularly gruesome story and thought "What the fuck?  Were these really written for children?"

Dwarves are a common feature of Teutonic (Germanic/Scandanavian) mythology and Jacob Grimm was certainly familiar with this having written a massive four-volume scholarly (for the time) set of books on Teutonic Mythology.

In mythology, dwarves aren't the cute, lovable characters we're familiar with from Disney movies.

Dwarves are much darker, black elves in some stories, and the original readers of Grimm would have envisioned dwarves as being much more unpleasant creatures.

One thing I found particularly interesting about dwarves is their association with mining.  Even the Disney dwarves went off to mine with their "Hi-ho" song.  If you love Tolkien's Middle Earth, as I do, you'll also know that dwarves in his story (and Tolkien was a scholar of mythology as well) built their cities in mines.  It's not just Germanic and Scandanavian mythology either, other cultures also had stories of little people who lived in the mountains mining precious metals and jewels.

Why this association between mining and dwarves?  Where did it come from?  I did a bit of searching and was unable to find much information.  This is an example of what I meant by the third type of geomythology - An association between a mythic figure or object and a geologic feature or phenomenon.

So, bottom line, I don't know why mining and dwarves go together.  If you have ideas, let me know!  Here are a couple of speculations...

Mines are mysterious.  Here locally, there are mines in the Shawangunk Ridge dating back to the 1700s mining primarily galena (PbS) for lead - there was also sphalerite, a zinc sulfide (ZnS), but I don't know if they had much use for zinc back then.  Anyway, there are now a number of abandoned adits, mostly flooded, and associated stories floating around the area that simply aren't true.  Some people are convinced they mined silver and gold in the area, for example, but it's most likely a layperson's misidentification of silvery galena or the iron sulfide (FeS2) pyrite ("fools gold").  One of the mines was known as the Old Spanish Mine with a preposterous legend about it being dug by the Spanish Conquistadores looking for gold.

Mine tunnels, especially old ones dug by hand, are generally small (ever try to tunnel through quartzite - it's harder than steel!).  It looks like they were dug by little people.  For all I know, maybe in ancient times naturally little people were used for mining because it would have been easier for them to maneuver around.

One of the classic books in geology is De Re Metallica by Georgius Agricola (1494-1555).  Agricola has some really interesting woodcuts in his book illustrating mining in Medieval Germany (click to enlarge).  Don't those miners look a little like the stereotypical image we have of mythical dwarves? Pointy shoes, funny hats, small stature? Does reality reflect mythology or vice versa?

A belief in little people in the mines may have even had a practical purpose.  Welsh and Cornish miners told tales of the tommyknockers.  While convenient foils to blame missing tools on ("the tommy knockers must have pinched it"), they also warned miners of impending cave ins by knocking on the mine walls.  Cracking open of fractures is indeed a warning sign of rock failure so it may well have been a good sign to leave if the tommyknockers started acting up!  Today, tommyknockers are mostly remembered by dint of their being mascots for a number of brew pubs out west.
Tomorrow, I'll talk abou another aspect of geomythology.  How discoveries of fossil bones may have inspired the legends of many mythological creatures we're all familiar with today.