October 4, 2012 by Chuck Bailey
My Geology 110 course, Earth’s Environmental Systems, is a big class. 195 students are enrolled and we meet for 50 minutes at 9 a.m. on Monday, Wednesday, and Friday. A big part of my job is to keep these 195 students engaged during our class meetings. This semester I am using LectureTools, a web-based software tool, that allows students to follow my presentations, ask questions, answer questions, and solve problems in class using their laptops, iPads, and smart phones. I get real time feedback from students: “Chuck, that last slide confused me”, “Chuck, please don’t put that question on the exam!”, etc. I ask questions and we can collectively see just how well they’ve done. Based on the answers I can change the pace or direction of the lecture. LectureTools has much promise. Thus far, the response from students ranges from mildly positive to robustly jubilant.
Understanding spatial relations on planet Earth is at the heart of understanding the Earth’s Environmental Systems. For many students, sorting out spatial relations is a challenge. We’ve considered solar elevation angles and insolation which leads to thinking about the Earth’s seasons and its axial tilt. Last Friday, I put up this satellite image of the Earth and asked:
On what day was this photo taken?
Notice the Earth is illuminated from its far northern reaches (Greenland) all the way to the Southern Ocean and Antarctica. The picture was taken by the Meteosat 9 satellite on September 22nd—the autumnal equinox (for the northern hemisphere). I expected it would be easy to tell that it was one of the equinoxes. But which equinox? The abundant sea ice in the Southern Ocean means that the region is emerging from its winter (the northern hemisphere’s summer). The results from my class were far different than my expectation. 61 of the students got the answer correct (that’s 37%), but 63% of the responses were incorrect and more people chose the summer solstice over the spring equinox. Yikes, we have a problem.
Having the results for everybody to see, immediately after students have answered a question is a great innovation. I then talked the class through the observations required to know that the image was taken on the autumnal equinox.
On Monday morning I tried a similar question on my charges.
Indeed this photo was obtained on the December solstice as evidenced by the illuminated region in the Antarctic and the darkness in the northern latitudes. A majority of the class got the question correct, but a sizable fraction was still confused. Better results, but not what I was hoping for. I followed this question with an annotated image illustrating a tilted Earth and a labeled equator. It’s all so easy when things are labeled!
On Wednesday I threw the class a related question and assumed that the third time would be the charm. LectureTools enables me to ask image questions in which students click on a map or an illustration to answer a question. My question concerned the current location of the subsolar point at 9:30 a.m. (EDT) on Wednesday, October 3rd. The subsolar point is the place on the planet where the Sun is directly overhead (solar elevation angle = 90˚).
The autumnal equinox had passed 10 days earlier, thus the subsolar point is a few degrees south of the equator. It was mid-morning in Williamsburg and in Greenwich, England (located on the Prime Meridian) it was mid-afternoon, thus noon (the time when the Sun reaches its zenith) was to the east of Williamsburg and to the west of Greenwich. The subsolar point at that moment was in the Atlantic Ocean to the east of Brazil.
A sizable fraction of the class placed the subsolar point in the Atlantic Ocean to the east of Brazil—nice work! Unfortunately, others placed the subsolar point in the northern hemisphere or worse yet, far to the north of the Tropic of Cancer (that never happens!). Not good news. But this in-class assessment paints a clear picture of what students grasp and, more importantly, don’t grasp. Back to the drawing board? I’ve got to figure out how best to help students learn these concepts and master spatial relations. I am a believer in “Practice Makes Perfect”, we shall see what the fourth try brings!
September 26, 2012 by Chuck Bailey
The James River’s basin spans much of Virginia. Its headwaters start amongst the high ridges of the Allegheny Mountains, and the river system covers some 700 kilometers (~400 miles) before debouching into the Chesapeake Bay at Hampton Roads. The river crosses four of Virginia’s five geologic provinces and exposes a wide array of rocks. Outcrops in and along the James provide key exposures for geologic research, and I’ve written about our numerous adventures on the river before. It is also an ideal watershed for reflecting upon hydrologic systems.
Last week a weathermaker crept northeast from Louisiana and brought rain to the mid-Atlantic on Tuesday the 18th. Some parts of the Appalachian Mountains received 3 to 5 inches of rain; eastern Virginia garnered less precipitation, but all in all it was a rainy day across the region. In the coming weeks I’ll ask my Earth’s Environmental Systems class to consider what happens throughout a drainage system when it rains, but this late September event was, dare I say, a textbook example of a flood wave passing through a basin and worthy of a post.
Watch the animated stream hydrograph of four U.S. Geological Survey gaging stations in the James River drainage basin to see the impact of this rainfall event. Before the arrival of the rain, the James and its tributaries were flowing steadily at relatively low late summer flow rates. The rain commenced late on Monday the 17th and continued throughout most of the day on Tuesday. The Bullpasture River, a small tributary stream in Highland County, responded with alacrity. At 9 a.m. on Tuesday the Bullpasture River had about 90 cubic feet of water passing down its channel every second (ft3/sec or cfs), by 3 p.m. the water level in the river jumped up by 5 feet, flow exceeded 4,000 cfs, and the stream was coursing above flood stage.
The rain came to an end on Tuesday evening. By that time flow on the Bullpasture was falling while the James River at Lick Run near Clifton Forge was about to start its climb, topping out at 6,400 cfs in the early morning on Wednesday. All the while, the James continued to flow placidly past the gaging stations in Scottsville and Richmond.
This pulse of water reached Scottsville on the morning of Thursday the 20th. Although the river never reached flood stage in Scottsville, the water rose ~3 feet in less than 3 hours and topped out with a flow of ~8,300 cfs just before midnight. It was mid day on the 20th when the James started a slow and sluggish rise in Richmond. The river continued to rise for over a day, eventually cresting at 11 p.m. on Friday the 21st. With a peak flow of 8,350 cfs in Richmond, the James did not reach its bank full discharge, but was well above the long term median flow.
The river distance between Clifton Forge and Richmond is ~350 km and it took the flood wave* nearly three days (65 hours actually) to traverse that distance. So what’s the average velocity of this pulse rolling down the river? After the river crested, all 4 hydrographs follow a similar trajectory with the flow dropping off exponentially over time. Why is the shape similar and what controls rate at which the hydrograph drops off?
Floods can wreak havoc on riverfront communities, especially if they arrive unannounced. But the surge from a storm through a drainage basin is relatively systematic and predictable. Upstream gage data make it possible to estimate both water height and the arrival time of high water, potentially averting dangerous situations. That’s one of the many reasons the U.S. Geological Survey gages rivers and it is a topic worth studying in the Earth’s Environmental Systems course.
*Although it did not actually flood along most of the James River, the concept is exactly the same.
August 29, 2012 by Chuck Bailey
William & Mary is back in business for another academic year. I teach my first class at 9 a.m. on Wednesday—Geology 110: The Earth’s Environmental Systems; it’s an introductory class with 200 students enrolled. Later, on Wednesday afternoon the College will gather for Convocation, and this is the ceremony that really kicks off the academic year.
In Earth’s Environmental Systems we’ll spend much time during the first week or two discussing the Sun and its relationship to the Earth. Consider the Sun and its path across the sky here on campus during the first day of the new semester, August 29th 2012.
The Sun will rise at about 6:36 a.m. (EDT) and will first appear above the horizon in the east-northeast. As morning progresses the Sun will rise ever higher in the sky, tracking out a southeasterly course. At local noon the Sun will be directly to the south and at its maximum solar elevation angle for the day (~62˚ on August 29th). Watch the animated graph to the see the path of the Sun across the Williamsburg sky.
Here’s a question: why, on August 29th, does local noon occur just after 1 p.m. rather than at 12 p.m.?
Insolation (incoming solar radiation) is the flow of solar energy intercepted by exposed surfaces. Insolation is a rate per unit area (watts/meter2). The amount of insolation received at any given point is a function of the solar elevation angle—the larger the solar elevation angle the greater the insolation. Insolation varies greatly as the solar elevation angle changes during the course of the day. Discerning how and why insolation varies across the Earth is fundamental to understanding the Earth’s environmental systems.
For many years Convocation has taken place in the courtyard of the Christopher Wren building, located on the west side of the Wren building. Convocation begins at 5:15 p.m. at that time the Sun will be 28˚ above the horizon at an azimuth of 260˚ (to the west-southwest), and as the ceremony rolls on the Sun will progress ever westward.
The Wren courtyard is well located to receive copious insolation during Convocation, and as such the temperature in the Wren courtyard is typically elevated to garish levels throughout the speeches and fanfare. Just ask the choir and faculty sitting in the courtyard, all tricked out in their robes and academic finery, about the temperature during Convocation. “It’s like being a disconsolate pig, all trussed up and stuffed into a three-sided brick oven…” groaned one of my colleagues. A three-side oven is an apt comparison as the vertical brick walls of the Wren building receive up to twice as much insolation as the nearby Earth’s surface, this heats up the bricks which, in turn, heat the surrounding air much more effectively than any blustery speaker ever could.
For this year’s Convocation, the College is moving the ceremony from the western courtyard to the eastern facade and front yard of the Wren building- what a brilliant idea! The venerable Wren building will provide shade for Convocation goers. After Convocation the incoming class of W&M students will proceed westward through the Wren building and emerge onto campus as the newest members of our community. This change in Convocation symmetry is a good idea. Paying due diligence to the physical reality of late August insolation and seeking a shady refuge in the Wren building’s eastern yard is a brilliant idea.
May 15, 2012 by Chuck Bailey
It’s just a day after commencement and I have landed in Arizona to await the arrival of 26 students enrolled in Geology 310: Regional Field Geology. The semester may be over, but the fun is not. Over the next three weeks we will traipse across the landscape of northern Arizona and Utah. We’ll study the geology of the Colorado Plateau from the bottom of the Grand Canyon to the top of the La Sal Mountains. This is the place where geologists go to see geology, well exposed and glorious. As access to the web permits, I’ll post status reports of our adventure.
May 3, 2012 by Chuck Bailey
The spring semester is rushing towards its conclusion. Classes have ended, final exams are underway, and graduation is just over a week away. The Geology Department’s class of 2012 is an accomplished and talented group. As I’ve noted before, all geology majors complete a year-long, independent senior thesis—this project is part of what makes the Geology experience at William & Mary unique. This year’s senior research projects were wide-ranging, from investigations of fossil shark tooth morphology, to lead geochemistry in New England soils, to magnetic anomalies in the Blue Ridge, to Mesozoic rift basin formation, and beyond! Two Saturday’s ago, the department came together for Senior Research Saturday, an eventful symposium in which seniors presented their research to friends, families, faculty, and peers. They played to a packed house and talks were followed by a suitably celebratory reception.
The class of 2012 not only talked up their science on campus, but also took to the road and presented the results of their research at professional meetings from Charlottesville to Asheville to San Francisco. Doug Rowland’s research on arsenic in groundwater at Jamestown was even highlighted by the History Channel. W&M geology students do meaningful research—but being able to effectively communicate that research is an essential part of being a public scientist. We put a strong emphasis on presentations in the Geology department and it’s rewarding to have our students showcase their research on a larger stage.
Earlier in the spring, our seniors led the departmental field trip and discussed their research at field sites from the Coastal Plain to the Blue Ridge Mountains. Watch a video from the trip and see for yourself! It is cool to see the geology seniors engaging their peers and teaching the faculty a thing or two! These activities don’t happen everywhere, but collaborative field trips and student leadership experiences are a delicious staple in the William & Mary Geology Department.
April 19, 2012 by Chuck Bailey
This past Friday, the Earth Structure & Dynamics class assembled behind the Geology Department and then poured themselves into 3 vans and headed west to the Appalachian Mountains. Counting supernumeraries we totaled 36 people, which qualifies as a mobile mob.
On this trip, students practice and hone their skills doing geology in the field and become familiar with the tectonic history of the Appalachian Mountains. Most years the trip runs in early April – a beautiful time of year in the mountains, but a time of year in which the weather can range from outright frozen to quite delightful. This year’s trip reveled in warm and dry weather. We camped in a valley cradled by Cambrian quartz sandstones – it was glorious.
Just how does this operation go down? Typically, we pull up to an outcrop or an overlook and the students debouch from the vehicles. I hand out sheets of paper with an array of tantalizing (or perhaps not so tantalizing) questions. Students work in teams of two and answer the questions; after the work is complete we discuss our answers and try to place the outcrop into the regional tectonic framework. We spent most of Saturday afternoon hiking and doing geology along the western slope of the Blue Ridge Mountains and from those data constructed a cross section of the geologic structure beneath us.
Back in the Paleozoic, when I was a student, we’d arrive at an outcrop and the professor would 1) prod us with questions until somebody shouted out the correct answer or 2) give us a mini- (or not so mini) lecture while we all stood around, passive and bored. My little worksheets are intended to get everybody thinking about geology. Students typically adopt a team name for the weekend, here is a sampling from this year’s trip: Gneiss-Gneiss Baby, team Diamonds in the Rough, team Paxtram, team Cococrisp, and who could forget team Big Boudins.
The days are running out on the spring semester and students are mighty busy, but this weekend field trip, far from the madding crowd, is an important piece in the education of W&M geologists as no amount of classroom or lab work can replace the hands-on experience of doing geology in the field.
March 6, 2012 by Chuck Bailey
My first post as a W&M blogger came after our Utah field season during the summer of 2008. Indeed, we lived the high life that July, conducting geologic research on the Fish Lake Plateau, a broad and broken highland situated nearly 2 miles above sea level. My undergraduate research students: Trevor Buckley, JoBeth Carbaugh, and Graham Lederer have graduated and moved on to success in graduate school and careers beyond the academy.
One of the areas in which we worked was Mount Hilgard, an iconic mountain that tops out at just over 3,500 meters (11,500 feet). What makes Mount Hilgard iconic is its curious shape. From the north the peak rises to a craggy summit while from the east or west it is asymmetric with a gentle southern flank and a steep northern rampart.
Mt. Hilgard owes its shape to the underlying geology, the peak is capped by a 250 meter thick sequence of volcanic rock erupted from gassy volcanoes 24 million years ago. The volcanic rocks unconformably overlie an older sequence of thinly-bedded mudstone and limestone. During the last 5 million years these rocks were uplifted, faulted, and tilted such that they are inclined about 10˚ towards the south. Gravity, water, and ice conspired to erode the bedrock: the volcanic rock stands as a hulking edifice that, over time, sheds copious debris onto the weak foundation of sedimentary rock below.
On July 23rd, 2008 Graham Lederer and I set off on our last traverse for the summer and climbed Mt. Hilgard to collect samples. On our descent we transited a block field composed of rubble accumulated at the base of the cliffs above, hiking down a block field is precarious work. A small bedrock outcrop (C99) provided a respite from the tortured descent. Further downslope (C100) my field notes tersely read, “bloody block field with mosquitoes- no bedrock here”. Much to our chagrin, surficial deposits effectively masked the underlying bedrock.
Take a look at the latest imagery (from July, 2011) of Mt. Hilgard available on Google Earth. A big chunk of the mountain’s east side moved downslope in the spring of 2011. In common parlance it’s a landslide, to a geologist it’s a debris flow. In 2008 we’d crossed the same patch of ground that later became entrained in this flow. Geology is a science in which time and place are important. Our traverse was in the wrong place, but at the right time!
This mass movement came downslope with enough velocity to flow up and over a small hill and continue a bit further down the other side. The flow terminates in a series of lobes about 800 meters (1/2 mile) below its origin. To put the scale of this mass movement into context, I plotted the outline of the flow onto an image of William & Mary’s campus. In this scene, the flow originated between Sadler Center and the Integrated Science Center. It would have flowed east, taking with it most of Old Campus, including the Geology Department, and grinding to a halt just before reaching North Boundary Street. The Mt. Hilgard event likely moved half-a-million cubic meters of material—that is quite a pile. These mass movement events play a large role in shaping this alpine landscape.
This summer I’ll be back on the Fish Lake Plateau with William & Mary students and we’ll head for the eastern slope of Mount Hilgard. Here we’ll do geology—examining the newly exposed bedrock and quantifying the 2011 mass movement event. No doubt we’ll stand on the debris flow surface and wonder, that if the time and place had both been wrong, would we have been able to outrun this debris flow as it roiled down Hilgard’s menacing flank? What do you think?
February 22, 2012 by Chuck Bailey
We are deep into the spring semester and my teaching/administrative duties are gobbling up most of my weekdays and nights. There is hardly a moment for research during the week, so research gets done on the weekends. I spent this past Saturday in the field searching for Hylas, the Hylas Fault Zone that is, not Hylas of Greek mythology. As the story goes, the mythological Hylas journeyed with the Argonauts, but while on an errand to fetch water he was abducted by nymphs. His mates searched in vain and Hylas was left to his fate. In 1976, Andy Bobyarchick described a zone of both ductile and brittle fault rocks near the small crossroads of Hylas, Virginia (~25 km northwest of Richmond) and the Hylas Fault Zone entered the geological literature.
Jump forward three and a half decades and John Hollis, a W&M geology major, has commenced his thesis research on understanding the brittle deformation history of the Hylas Fault Zone. During the past six months, John sought out exposures of bedrock in stream valleys and quarries to understand the structural geology of these rocks. On Saturday we put a canoe into the North Anna River: a floating traverse across the eastern Piedmont in search of the Hylas Fault Zone.
For February, the weather could not have been better (although a bit on the chilly side for nymphs). The North Anna was similarly cooperative, flowing at a comfortable rate that easily floated the boat, but left most of the bedrock outcrops above the waterline. We glided by a veritable menagerie of metamorphic rocks in the enigmatic Goochland Terrane, examining thinly layered gneisses, coarsely banded gneisses, pegmatitic gneisses, biotite-garnet schists, and amphibolites. We measured the orientation of ductile and brittle structures in these impressive channel and riverside cliff outcrops.
Halfway into the trip we lunched at a large low outcrop of biotite-garnet gneiss cut by two generations of brittle fractures. Immediately northeast of the river stood the stone foundations and derelict chimney of Jericho Mills. In May 1864, Jericho Mills formed a major crossing point for the Union Army as it pressed south against the Confederate Army. A photo dated May 24th 1864 by Timothy O’Sullivan shows a pontoon bridge spanning the North Anna just upstream from the mill and the same outcrop upon which we lunched, measured structures, and collected a sample 148 years later. For me, this nexus of human history, geologic history, and now my personal experience defies easy description but is somwehere between surreal and cool. O’Sullivan’s photos illustrate that the terrain bordering the North Anna was mostly open country during the Civil War: today that same terrain is cloaked in forest and the vestiges of past human activities are greatly muted. On this tranquil float, it was difficult to conceive that we transited a battleground on which more than 5,000 Americans were either killed or wounded during those four days of fighting long ago.
The North Anna flows with a subdued gradient across the Piedmont, but in the last few kilometers before arriving at the Coastal Plain the river drops through a sequence of rapids that define the Fall Zone. These rapids got our attention as we coursed quickly past the bedrock in whitewater. After negotiating the big Fall Zone rapid we caught our breath on the broken rocks on the east side of the Hylas Fault Zone. These rocks have enjoyed more deformation than most: when these rocks were hot, but not molten, they were sheared and squeezed. Later these rocks were fractured, faulted, and mineralized. A suite of narrow jagged veins angle through the rock, these veins look suspiciously like pseudotachylite. Pseudo what? Pseudotachylite is a dark glassy fault rock formed by frictional heating, melting, and subsequent quenching. These veins may record paleoearthquakes in the Hylas Fault Zone.
Just below the rapids, we quietly glided over the Fork Church Fault, the eastern boundary to the Hylas Fault Zone. Although we never saw the Fork Church Fault, it is a whopper of a normal fault with thousands of meters of slip and it forms the boundary fault to the Taylorsville Mesozoic basin. We were delighted by the mossy outcrop of boulder conglomerate that signaled our arrival in the Triassic rift basin. The character of the North Anna changed dramatically as well: the Fall Zone rapids were behind us, bedrock outcrops became sparse, and the river birches formed a nearly unbroken canopy above the river. Another research adventure complete, we pulled the canoe off the water in growing twilight.
We learned much from our float trip. John has a heap of new data to chew on and incorporate into his thesis. Some of our observations don’t jive with previous studies and we’ve got a host of new questions about the regional geology. Geologists are fortunate in that the field is commonly where we go to collect our primary data. Although time consuming, fieldwork is often sublime and beautiful.
February 3, 2012 by Chuck Bailey
William & Mary is celebrating its 319th birthday this weekend. For an institution of higher learning in the western hemisphere, 319 years certainly qualifies as venerable. Although what qualifies as old depends on your perspective; geologists typically take a long view on time. It’s easy to do when you consider that the Earth’s history stretches out to well over four billion years.
Consider the photograph below, a little snippet of bedrock cropping out high above Harris Cove in the Blue Ridge Mountains of western Virginia. The rock is a gneiss (pronounced- nice!), a curiously colorful granitic gneiss. This is an ancient rock, it crystallized and cooled into a granite, far below the Earth’s surface, some 1.15 billion years ago. It was later metamorphosed and transformed to a coarsely-foliated gneiss. By the late Neoproterozoic (~550 million years ago) the rock was exposed at the surface and then buried beneath a sequence of lava flows and sedimentary deposits. At some point the rock underwent another transformation and the iron-bearing minerals were altered into a new mineral, epidote—a distinctive greenish silicate, while the feldspar turned pink. Indeed, it’s an old rock with quite a history.
Field geologists take oodles of rock pictures and invariably we include some marker to provide ‘scale’ for the picture. I’ve used rock hammers, lens caps, pocketknives, and even doughnuts to provide scale. Coins are a time-honored standard, in part because the local currency imparts a certain authenticity to your whereabouts (e.g. loonies in Canada, kangaroo dollars in Australia, and Eva Perón pesos in Argentina). Take another look at the coin I used for scale. Just whose faces are those emblazoned on the not-quite-round coin? Why, it’s our very own King William (GVLIELMVS) & Queen Mary (MARIA) on a weathered threepence from the days of the Glorious Revolution in the late 17th century. The coin is 18 mm in diameter (roughly the size of a dime) and a gift from my coin-collecting father.
It’s nice (or is that gneiss?) to be old and good to see William & Mary out and about! Happy Charter Day.