Posts

The Volcano Near Fairfax County

A photograph of Mole Hill as seen along Route 33.

Article and photo by FMN Stephen Tzikas

When I travel to the Society of Amateur Radio Astronomers (SARA) annual conference every summer at the Greenbank Observatory in West Virginia, I drive along Route 33 just past Harrisonburg, VA, the home of James Madison University (JMU). It’s a rural road, but something unusual is found there – a volcano. It’s called Mole Hill, quite inactive today, but nearly 50 million years ago magma thrusted upwards to the surface through cracks in the lithosphere. The tree covered Mole Hill as seen today is made of remnants of the cooled magma column, eroding at a slower pace than the sedimentary rock around it. That resistant rock that supports the peak is a volcanic plug of olivine basalt. This basalt is dark greenish gray to grayish black, medium grained, and moderately porphyritic. Mole Hill is one of the youngest volcanoes on the east coast of North America. Mole Hill has a height of nearly 1,900 feet above sea level. Another extinct volcano, Trimble Knob, is a little closer to the Greenbank Observatory and a little farther from Fairfax County.

Dr. W. Cullen Sherwood of JMU, who passed away in 2016, gave a brief account of Mole Hill and its geology at the following link: https://csmgeo.csm.jmu.edu/geollab/vageol/outreach/fieldtrips/rockingham/molehill.html

His illustration gives the reader an idea of how Mole Hill may have originally appeared.

Mole Hill is mentioned in the Roadside Geology of Virginia book by Keith Frye. The books in the Roadside Geology Series are an excellent way to explore the geology around us when we travel along roads through different states. These books are available through Amazon.com.

 

Triassic Rocks of Horsepen Run

Muscovite mica glitter is apparent in a rock sample from Horsepen Run.

Article and photos by FMN Stephen Tzikas

Part of the Horsepen Run watershed is located in the northwestern part of Fairfax County. Horsepen Run eventually drains into the Potomac River. The trail that follows the creek in the watershed is popular with county residents. A part of the creek is also one of the regular sites of biological stream monitoring, a volunteer citizen science program managed by the Northern Virginia Soil and Water Conservation District. What a lot of people don’t know is that Horsepen Run is home to some interesting Triassic Period rocks, formed some 200 to 250 million years ago. A few years ago I participated in a geological field trip excursion as part of a NVCC 1-day 1-credit course that explored the geologic history of Mesozoic Era rift basin across the Manassas, Leesburg, and Haymarket areas. The excursion was specific to the Triassic and Jurassic Periods. Specific items of interest were the weathering of products; direction of transport; sediment structures; igneous rock textures and their cooling history, the rock cycle, and plate tectonics.

One of the sites investigated was the Dulles Access Road East “utility” off-road on the exit ramp for Rt. 28, at Horsepen Run. This site was the central point of a rift valley deep with sediments. Specifically, it was a lake bottom of red sediment. Some shale exists, breaking into sheets and fine grain. The rift was formed when the Earth

Horsepen Run creek at this location is composed of characteristic red rock: TRb Balls Bluff siltstone, both creek bottom and the adjacent 1-2 foot walls.

was pulled apart at the location. The rift valley is the linear shaped lowland between higher hilly and mountainous elevations created by the action of a geologic rift. Such valleys are likely to be filled with sedimentary deposits derived from the rift flanks and the surrounding areas. At this location the rock type contains Upper Triassic Balls Bluff Siltstone baked and thermally altered material. The red sediment at the location is obvious and contrasts with the appearance further upstream. The glitter found in the red rocks at this location are tiny fragments of mica.

In the Triassic Period, this site was tranquil and sediments came to rest. At the Horsepen Run area, bubbles on the surface of the sediment rock indicate a calcareous (calcium based) dissolved appearance where the red rock voids still have some calcium carbonate (scattered white tones on the rocks). Occasional storms brought water from outlying edges to the center and carried some coarser material. A storm deposit from the west could bring calcium carbonate from the Leesburg conglomerate. A storm deposit episode or event could last minutes to hours.

The lacustrine (lake) facies indicated an oxygen rich environment with red color clastic deposits, allowing the oxidation of the iron. This is facies evidence, referencing the look of rock to respect of environment. If there was no oxygen we would have found black shale. Low energy would have been required for the fine grain to come to rest. Fine grains could also be due to a deep environment, but here it was more likely a shallow one of 10-15 feet, where sediments could dry. This area was a cove of low energy closed lake basin water, subject to evaporation effects. Some “circle fossil” burrow tubes also exist in the fine grain clays. Burrowing organisms lived here causing bioturbation. More evidence of the oxygen rich condition is that the taphonomic conditions were not ideal for preservation, as oxygen rich area deaths led to scavenging and organic breakdown. The terraced layers at the site alternated between siltstone and claystone, caused by changes of energy due to rainfall and climate. Higher energy means more shallow depth silt: wave energy takes away clay silt by the beach. If the climate was a little dryer, the lake would shrink, alternating between shallow and deeper cycles. These climatic cycles were tied to the Milankovitch cycles of variations in the Earth’s eccentricity, axial tilt, and precession.

You also might find some of the glittery red rocks in the surrounding area near Horsepen Run. Recently I visited the EatLoco Farmers Market at One Loudoun near Dulles airport. Between the parking lot and the vendor stalls is a strip of ground, part grassy and part flat thin red rock chips, not unlike what is found at the Horsepen Run site.

Geology Adventures: Man-Made Slag

Feature photo:  Slag Nuggets line this railroad track near Willoughby Brook, High Bridge, NJ

Article and photos by FMN Stephen Tzikas

Not too far from Fairfax County is geologic treasure. Engineers love it. It is a by-product of iron ore smelting, one of the oldest chemical engineering processes. The by-product is called slag and it is unique and beautiful.

A few years ago I stopped at the Burden Iron Works in Troy, NY on my way to Rensselaer Polytechnic Institute (RPI) for Reunion and Homecoming not far from the iron works. The iron works are not a big tourist attraction, so I had to call the curator for an appointment. The meeting I had with curator was just grand. We talked at least a couple hours on the engineering history of the area which included RPI. Before leaving he took me outside to walk the perimeter of the iron works

Catoctin Furnace Slag Nugget Sample 1.  Vesicles pockmark this brownish and green tone slag sample.

and told me about slag. Slag is the rock remaining after iron is extracted from the ore. The property and surrounding area has some slag scattered around. He told me it can usually be found easily along a building perimeter because that’s where it’s thrown by ground keepers who cut grass and don’t like hitting it with the mowers. He gave me a few pieces of the century-plus old slag and I finally departed.

Later, at the Jonsson-Rowland Science Center building at RPI, while looking at the geologic collection located there, a graduate student came out of his research lab and I struck up a conversation with him on the Burden Iron Works. He quickly went back into his lab to pull out a slag sample from the iron works in which some residue ore in a large slag sample formed a colorful blue glass mix with the ore. Impressed, I have ever since included old iron furnace stops on my road trips. If you keep in mind that slag samples are likely to be located along perimeter building ruins, you’ll find interesting nuggets. One especially pleasing location is the Lock Ridge Furnace Museum if you are passing through the Allentown, PA area. There are literally thousands of slag samples all over the grounds. It is much rarer to find slag samples with colorful shades of glass in them, but if you are curious, do a google image search on “colored iron slag” to see what I mean. Some slag samples can also be magnetic, and the color of a slag sample is due to the different mixes of elements and leftover metals in it.

Catoctin Furnace Slag Nugget Sample 2. Vesicles and Blebs are found in this gray slag sample.

Iron smelting was a big industry in the 18th and 19th century America, and you can usually find industrial furnace ruins from that period everywhere that had settlements. My stops at old furnaces usually take me through Pennsylvania on my trips to NJ and NY. However, we have local furnace ruins too. One nearby is the Catoctin Furnace in Thurmont, MD. This is a 19th century iron works and the website can be found at https://catoctinfurnace.org/village/

Slag samples could appear in a variety of other places too. The iron industry of yesteryear produced so much slag waste, the industry found uses for it. Iron ore slag is generally safe. It is just ore rock with the iron removed. While hiking in High Bridge, NJ one day, I came across large amounts of it lining the railroad tracks (along Buffalo Hollow Road near Willoughby Brook, and just off of Cregar Road). The slag made a suitable material cushioning the track area from the extended environment. Normally, one might see other forms of crushed stone gravel around railroad tracks. If you come across railroad tracks in your nature trail excursions, take a look at whether the tracks have stone ballast in the track bed, and whether it is slag.

If I have interested you to build a slag collection, please be aware that some parks might have rules requiring visitors not to remove anything from a site. Such rules, if they exist, are usually posted so visitors know. Now that you are aware, keep your eyes open for interesting geology on the ground at old furnace ruins.

 

Below the Surface: How Plants & Geology Interact, webinars March 8th & 15th

Tuesdays, March 8 and 15, 2022
6:30 pm, meet and greet both evenings
Sessions start at 7pm and 8pm both evenings
Please register only once for both sessions

Join Virginia Native Plant Society for either or both evenings on geology and plants. March 8th’s sessions topics are Land Management Lessons from Piedmont Prairies and Virginia’s Geology. On March 15th the topics are Geology and Soil Parent Materials as Determinants of Natural Communities in Virginia and the Carolinas and Beyond Substrates.

Keep learning with Smithsonian Museum of Natural History webcasts

Smithsonian Science How

Bring a Smithsonian Scientist into your classroom with Smithsonian Science How! Check out the Science How schedule below to get started, or preview our formats by watching a program from our video webcast archives.

Video Webcasts

These free, interactive, live video webcasts take questions from your students while introducing them to science concepts and practices through the lens of Smithsonian research and experts. The shows provide opportunities for your students to interact via live polls and Q&A with the scientist.

  • Grades 3-8; optimized for students in grades 3-5
  • Developed in collaboration with the Smithsonian’s children’s theater, Discovery Theater
  • Scientists take your questions
  • Complementary teaching resources
  • 30 minutes long
  • Aligned with national science standards

Schedule

Here is the webcast schedule for the 2019-2020 school year. Want to suggest a topic for a future show? E-mail us at ScienceHow@si.edu.

Upcoming Shows

We’re moving our popular webcast series to video webinars to connect your learners to natural history science and careers more often. Webinars will be presented on Zoom video. All times are Eastern Time.

Completed Shows

Video Archives

We’ve produced 52 Smithsonian Science How webcasts over the last six years. They feature Smithsonian experts and cover specific topics in the disciplines of Earth Science, Life Science, Paleontology, and Social Studies.

Browse the video archives.

Ask Science How

Teachers and students: Do you have a question for our science experts? Send us your questions, either before or after a webcast. We’ll send you the answer. Ask Science How

Learn at The Nature Foundation Spring Wildflower Symposium

18-20 May

Wintergreen Resort, Route 664
Wintergreen, VA 22958

Register by 20 April to receive an early registration discount

Presented by The Nature Foundation, for over 30 years Wintergreen’s Spring Wildflower Symposium has offered the best and most diverse coverage of wildflowers and mountain ecosystems. The setting is unique, with over 30 miles of hiking trails and convenient access to diverse geological sites. No one comes away from this event without learning more about botany, geology, entomology, ornithology and ecology. And all of this is available in the most beautiful springtime region in Virginia.  Learn more here.