The Falls of the Rappahannock EarthCache

The Falls of the Rappahannock

The questions and a warning...

As a courtesy to my fellow cachers, I have placed the questions you need to answer at the beginning of this page, so that they do not get truncated by gps units that can only display a limited amount of text in the description. Please take a moment to read through the rest of the description to discover why this place is so special, thank you.

In order to log this earthcache you must answer these questions, and post your picture to the cache page. You must also exercise caution, while this location is safe, the water is not. Do not do anything that could cause you to fall into the water, as there is a significant chance of injury or drowning if you enter the water above the fall line. When using your gps to record elevations, shoot them from the beaches not the rocks. This is a beautiful spot, but like many of nature's beauties it has it's own dangers and must be respected. I should also mention that the island is connected to the shore by a man-made structure that I have always used to access it. Now on to the important stuff:

1. Proceed to the rock outcropping at the posted coordinates and take a picture of your group to post to this page. Here is an example of a picture of Scoot the Frog and StShelby taken at these coordinates.

2. Walk to the upstream end of this island and use your gps to record the elevation of the water level.

3. While on the upstream end of the island note the geological makeup of this island, what does this tell you about it's creation and survival in this tumultuous area. What is the main difference between the upstream and downstream ends of the island.

4. Head back to the mainland and proceed downstream to any point below the fall line, use your gps to record the elevation of the water level. How far has the water dropped as it crosses the fall line.

The Falls

The Rappahannock River is a river in eastern Virginia in the United States, approximately 184 miles in length. It traverses the entire northern part of the state, from the Blue Ridge Mountains in the west across the Piedmont to Chesapeake Bay south of the Potomac. It is considered by some to have been the boundary between the "North" and the "South" during the Civil War, which are geographic regions still referenced today. An important river in U.S. history, it was the site of early settlements in the Virginia Colony and was later a major theater of battle in the American Civil War. It drains an area of 2,848 square miles, approximately 6% of the state of Virginia.
The name of the river comes from an Algonquian language word lappihanne (also noted as toppehannock), meaning "river of quick, rising water" or "where the tide ebbs and flows." This name was taken from the name given to it by the local native population the Rappahannock Tribe.
The Rappahannock River begins as streams flowing from the eastern slopes of the Blue Ridge mountains, flows southeast through the fall line at Fredericksburg (where freshwater and tidal effects meet), and ends as a wide estuarine river that meets the Chesapeake Bay. The Rappahannock river is joined by the Rapidan river at a confluence approximately ten miles northwest of Fredericksburg. The Rappahannock River basin is 2,725 square miles in area, with a maximum width of fifty miles in the headwaters, and a minimum width of ten miles just north of Fredericksburg. There is also an additional 2,432 miles of streams and rivers within the basin providing an abundance of water resources.

The underlying strata of the eastern seaboard along the Fall Line.

The Fall Line

The Fall Line is a low east-facing cliff paralleling the Atlantic coastline from New Jersey to the Carolinas. It separates hard Paleozoic metamorphic rocks of the Appalachian Piedmont to the west from the softer, gently dipping Mesozoic and Tertiary sedimentary rocks of the Coastal Plain. This erosional scarp, the site of many waterfalls, hosted flume- and water-wheel-powered industries in colonial times and thus helped determine the location of such major cities as Philadelphia, Baltimore, Washington, and Richmond.

The interstate highway is a rough guide to the location of a geologic boundary known as the Fall Line, which is the boundary separating the soft Coastal Plain from the hard Piedmont. East of I-95, the soil is sandy, it is light-colored (sometimes almost yellow or even white), and there are few hills. West of the interstate, the plowed fields expose red clay and the land rises steadily to the Blue Ridge, the eastern edge of the Valley and Ridge. The Piedmont rock was once the soft sediments of the Outer Continental Shelf, and located offshore from the ancient shoreline of Virginia in the Iapetus Ocean. When Africa and Europe bumped into the North American continent and created the Appalachian Mountains, those soft sediments were scrunched up from the ocean bottom and pushed onto the North American continent. In the process of being scrunched, the sediments from the Iapetus Ocean floor were squeezed and baked into the hard metamorphic rock that now underlies much of Virginia between I-95 and the Blue Ridge. The metamorphosed sediments are exposed at many spots along the fall line including Great Falls on the Potomac River, just upstream from Washington, DC and the Falls of the Rappahannock, here in Fredericksburg.

After the continents collided and formed the Appalachians, the continents then split and formed the Atlantic Ocean. When it opened, the Virginia shoreline was at the eastern edge of the Piedmont. Since then, sediments have washed down as the mountains eroded. Those sediments have accumulated east of the Piedmont to form the Coastal Plain. In addition, the water levels in the Atlantic Ocean have risen at times, and deposited more sediments east of the Piedmont to increase the extent of the Coastal Plain. Those relatively recent Coastal Plain sediments, formed by freshwater rivers eroding the modern Appalachian Mountains and by deposition when ocean levels were higher, have not been baked and squeezed tight like the Piedmont bedrock and are much more subject to the effects of erosion.

When the Rappahannock flows eastward from the Piedmont onto the Coastal Plain, it leaves a zone where the riverbottom is hard rock and encounter easier-to-erode Coastal Plain sediments. The energy of the water carves a deeper channel in the softer sediments, creating waterfalls. This edge of the Piedmont/Coastal Plain is marked by a line of waterfalls (the Fall Line) where various rivers move from harder to softer bedrock.

These photos show the effects of the Fall Line on the navigability of the Rappahannock. These photos were taken within 15 minutes of each other less than 1.5 miles apart.

The waterfalls are most obvious at Great Falls on the Potomac River, on the Rappahannock River at Fredericksburg, and on the James River near downtown Richmond. The waterfall on the Occoquan River near Lorton has been "dried out" by the construction of a dam, trapping the water in the Occoquan Reservoir, but you can see the exposed rocks at the Fall Line by walking upstream from the town of Occoquan. The Fall Line is a zone - sometimes several miles wide, rather than just a narrow line - between the Coastal Plain and the Piedmont physiographic provinces. The bedrock in the Piedmont is the hard crystalline rock that you can see at this location and the sandy beach just below this spot is evidence of the soil structure of the coastal plain that this line marks the boundary of.

Email your answers to me and log the cache.

I hope that you enjoy your visit to this beautiful location, I visit every time I am nearby and I really love it here. While reading an article about the fall line a couple of weeks ago, I thought about how this island is a microcosm of what is happening in the surrounding area, and how this would make it the perfect classroom in which to learn about the Fall Line while enjoying this wonder of nature. Have fun and be careful out there.