The Earth Story

The Appalachian Bend

The Appalachian mountain chain extends just over 2400km (1500 miles), and is one of the most famous long-distance hiking trails in the world. Seen from a birds-eye view, the chain runs a nearly straight line from Alabama, USA, to Newfoundland, Canada, except for a mysterious bend in the states of Pennsylvania and New York.

The Appalachian mountain range formed more than 300 million years ago when the African and North American plates collided, making the latter fold and wrinkle as it was pushed westward, forming the ridges we know today. For some time, geologists have known of a rigid, volcanic rock structure under the Appalachians, but didn’t understand the size or its implications for mountain-building processes.

Professor Cindy Ebinger of the University of Rochester and associate professor Margaret Benoit of the College of New Jersey, together with their research team, sifted through the North American Gravity Database, which contains two decades worth of measurements of the gravitational pull over the North American terrain. They managed to determine the density of the volcanic rock and estimated its dimensions to be 450 km by 100km (280 by 62 miles). The massive size of the structure acted as a barricade forcing the mountain range to form with a bend.

Ebinger called the research project a “founding study” and hopes that it will improve the understanding of the Earth’s underlying structures. She believes that the findings could provide valuable information in the debate over hydraulic fracturing.

~ SW

The study published in the journal Earth and Planetary Science Letters: http://www.sciencedirect.com/science/article/pii/S0012821X14002246 More Info: http://www.rochester.edu/newscenter/the-bend-in-the-appalachian-mountain-chain-is-finally-explained/ http://earthobservatory.nasa.gov/IOTD/view.php?id=84393

Photo Credit: NASA / Stuart Rankin -http://bit.ly/1xT2Gwt

Fairy Stone Park

The story of these little crystals begins over 500 million years ago as sedimentary rocks were deposited along the coastline of a continent we call Laurentia – predecessor to modern day North America. Those sediments were deposited in a passive margin – an area with no active continental boundary, formed when the supercontinent Rodinia rifted apart to form a new ocean. 300 million years ago or so, that ocean closed as what is today Northwest Africa collided with eastern Laurentia, uplifting a huge mountain range. The sediments that were originally deposited off the coast of Laurentia were trapped in this mountain range. They were shoved deep into the Earth’s crust and heated, so much so that the minerals in the rock changed – making the sediments into a metamorphic rock.

One of the metamorphic minerals produced under these conditions is the mineral staurolite. Staurolite has a neat property to its structure called twinning – the layers of atoms that make up the mineral will sometimes shift along a plane or surface inside the mineral, and they do so in specific patterns. Staurolite twins by creating either 60 or 90 degree angles inside the crystal – basically forming two crystals that interlock, into a cross shape.

These staurolite crystals grew during the metamorphic event caused as the Appalachians formed. Eventually Africa and North America separated and these rocks were pulled back to the surface by new faults and erosion of the mountains above. As they cooled off, the staurolite converted to sericite, a lower-temperature mineral, without changing shape – a process called pseudomorphing (one mineral in the shape of another).

Given the religious significance of the cross shape, and the fact that they’re just neat in the first place, it’s not hard to see why these stones became collectable. Even imperfect stones can be used – the sericite is soft enough to be easily cleaned and polished and shaped into perfect crosses. In fact, I even found a literature reference from 1934 of one of them being polished into a Swastika. These stones are picked out of Fairy Stone State Park in Virginia – they are free to collect as long as you use only your hands and pay admission/parking fees in the park.

-JBB

Image credits: https://flic.kr/p/Lnt755 https://flic.kr/p/eHbiBu https://flic.kr/p/AsSCaG

References: http://www.dcr.virginia.gov/…/blog/legend-of-the-fairy-stone http://www.minsocam.org/ammin/AM19/AM19_549.pdf

Fulbright students examining an outcrop in West Virginia

Number of different shots takes you on a tour of Letchworth Falls, New York

Awesome view - cliffs in Minnewaska State Park Preserve, New York state - sedimentary rocks made of material eroded as the Appalachians were growing, now marking the edge of the mountains.

Learn about Appalachiosaurus, a Tyrannosaurid relative from the Eastern U.S.

Hills of West Virginia

A trip through the Appalachian Highlands and Blue Ridge Mountains of Western North Carolina.

GREAT SMOKY MOUNTAINS

The Great Smoky Mountains, which lie between Tennessee and North Carolina, are part of the highest and southern-most portion of the Appalachian Mountains. The “Smokies” are named for a haze of smoke that hangs over the area that originates from the bodies of water in the park (streams and waterfalls) interacting with abundant vegetation. Great Smoky Mountains National Park is 2072 square kilometers (800 square miles) in total area and holds more than 17,000 species; scientists estimate there are thousands more that have yet to be documented in the area. The mountains contain incredible biodiversity. There are approximately 100 tree species in the park, and 25% of the forested areas are classified as old-growth forest. Due to the high biodiversity found in the park, the United Nations has declared it an International Biosphere Reserve.

The wide variety of species is attributed to the shape of the mountains and their geologic history. The diversity of the elevations in the park, spanning a range from 266.7 meters to 2,024.8 meters (875 to 6,643 feet), creates many different environments in which diverse species make their homes. The Great Smoky Mountains are also some of the oldest mountains in the world, having formed 200 to 300 million years ago, and are arranged from a northeast to southwest direction. During major climatic shifts such as the last ice age in the region 10,000 years ago, species migrated across these mountains because they were not affected by glaciation due to their southern location. The mountains also experience extensive precipitation, leading to abundant plant growth.

The Smokies have a complex and ancient geological history. Initially, the rocks that made up the area were sedimentary, composed primarily of clays, silts, sands, gravels and limited amounts of calcium carbonate. The oldest rocks are approximately 800 million years old in these deposited flat layers. Nearby highlands made of granite and gneiss were weathered, creating sediments that were washed down into lower areas. The age of the rocks in the highlands is estimated to be one billion years old. The weathered material formed the coast of the ancient North American continent during the breaking up of an ancient super-continent. The mountains that we see today were formed when the ancient North American continent collided with ancient Africa and Europe, and closed an early Atlantic Ocean; this reunited the landmasses. This collision, and subsequent uplifting and metamorphosing of the rocks, created the Appalachian Mountains, a mountain chain that spans from Canada to Georgia and was part of the super-continent Pangaea. The Smokies are in the southern portion of this mountain chain. Today, the Smokies are lower than they were due to erosion. Scientists estimate that some areas of the mountains are being worn down approximately two inches every thousand years.

There is some debate as to whether the Smokies are still experiencing uplifting forces, since they possess very distinct features (i.e. steep slopes, high relief, river-incised gorges, frequent mass-wasting occurrences) that seem to indicate that the landscape is changing. Some areas of the region have even experienced uplift of 150% since the Miocene epoch. One explanation for these features is variable erosion of rock layers that make up the mountains. A competing hypothesis explains that the region is still tectonically active due to forces in the Earth’s mantle causing uplift.

If you like hiking, the tall (and potentially growing) Smokies are a great place for you to visit. I spent a day hiking there this past November after a recent snowfall and took some amazing photos. Just be careful—the incredible ecosystems that the Smoky Mountains provide are also home to approximately 1,500 black bears. This is one of the few places in the eastern United States where black bears still live in the wild.

-Jeanne K.

I took this photo while hiking the Great Smoky Mountains in November 2012. I hope you enjoy it!

References: http://www.nps.gov/grsm/naturescience/index.htm

http://www.nps.gov/grsm/naturescience/environmentalfactors.htm

http://geology.er.usgs.gov/eespteam/smoky/ResearchAreas/smokys/MountLeConte/geology1.htm

http://www.nps.gov/grsm/naturescience/geology.htm

http://memory.loc.gov/ammem/gmdhtml/nphtml/gsmhome.html

http://www.nps.gov/grsm/naturescience/black-bears.htm

http://www.geosociety.org/gsatoday/archive/23/2/article/i1052-5173-23-2-4.htm