Grafton Ponds Earthcache EarthCache
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
This earthcache takes you to sinkholes in the Grafton Ponds Natural Area Preserve, part of Newport News Park, and will teach you about the geology behind the ponds here.
There is no physical cache container to find; to log this earthcache, you will need to email or message us the answers to the questions below. The questions are repeated in the unencrypted hint for your convenience.
If you are parking at the south parking area off Fort Eustis Highway, please do not block the gates in case emergency vehicles need access. After a short dirt patch, access is an easy 1 mile walk on an old paved road.
THE YORKTOWN FORMATION
Based on current scientific theory, around five million years ago, during the time known as the late Miocene epoch, everything you see around you was at the bottom of the Yorktown Sea. Back then, the Virginia coastline was about 40 miles further west, running roughly north to south through what is now Richmond. The Yorktown Sea was warm, shallow, and tropical, teeming with life, especially mollusks (shellfish and snails). Temperatures were around 2.5 ̊ C (4.5 ̊ F) warmer than today.
Over time, deposits thickened at the bottom of the ocean and began to cement together in places. Sand, clay, silt, and especially shells formed a sedimentary layer now called the Yorktown Formation. Originally hundreds of feet thick, the formation weathered away over time. In some places, such as north at the bluffs along the York River, the Yorktown Formation remains thick and is visible above ground.
KARST TERRAIN
The ponds and depressions in this area are sinkholes, examples of karst terrain. As rain falls through the atmosphere, carbon dioxide dissolves into the water, creating a weakly acidic solution called carbonic acid. This water can become more acidic once it hits ground as it passes through decaying organic matter such as leaves.
In Virginia, karst terrain is more prominent in areas that have limestone rock, such as the Valley and Ridge region between the Blue Ridge Mountains and the Appalachian Plateau. However, even though the Yorktown Formation isn’t dense enough to support cave systems, it has developed sinkholes.
HOW THE SINKHOLES FORMED
As acidic groundwater sank through the Yorktown Formation, it reached pockets of shell-rich layers in the sediment. The shells, made primarily of calcium carbonate, dissolved, causing the surface above the now empty pocket to collapse into a sinkhole. Some of the resulting depressions are underlain by layers of clay, which help hold water in the sink and form ponds. Some of these ponds are full of water year-round; most are seasonal, filling with water in the rainier winter and spring months and drying up in the hot summers.
While this area of York County contains the greatest concentration of sinkholes, the whole area is susceptible to sinkhole formation. In the early 2000s, a large sinkhole formed in a yard in the Queens Creek subdivision near Williamsburg, forming a wetland.
These small patches of wetlands are incredibly diverse and can contain rare species of plants and animals, including orchids. The health of these small ecosystems is threatened by invasive species, such as Nepalese browntop and Japanese honeysuckle. Human activity such as new housing developments and fertilizer runoff also threaten the ponds. The Grafton Ponds Natural Area Preserve was established in 1995; the City of Newport News set aside 375 acres on both sides of Fort Eustis Highway in order to protect over 100 ponds.
LOGGING THIS EARTHCACHE
To log this earthcache, send us a message (visit link) or an email and copy and paste these questions, along with your answers. Please *DO NOT* post the answers in your log, even if encrypted. There's no need to wait for confirmation from us before you log, but we will reply to messages and to emails if you include your email address. Group answers are fine; just let us know who was with you.
1. The name of this earthcache: Grafton Ponds Earthcache
2. In your own words, how did the sinkholes form?
3. Describe the pond at the listed coordinates. Based on your observations, do you think this pond at the coordinates holds water year-round? Why or why not?
4. (Optional) Compare the pond at the listed coordinates to one (or both) of the ponds at the additional waypoints. Do you think this second pond (or these other two ponds) hold water year round? Why or why not?
Photos of your visit are optional but highly encouraged and greatly appreciated.
SOURCES
Bob Moss, "Geology of Virginia," American Society of Highway Engineers, 2014. (visit link)
J.E. Hazel, "Ostracode biostratigraphy of the Yorktown Formation (upper Miocene and lower Pliocene) of Virginia and North Carolina," US Geological Survey Professional Paper 704, 1971. (visit link)
L.W. Ward and B.W. Blackwelder, "Stratigraphic revision of Upper Miocene and Lower Pliocene beds of the Chesapeake Group, middle Atlantic Coastal Plain," US Geological Survey Bulletin 1482-D, 1980. (visit link)
Virginia Department of Mines, Minerals, and Energy, Division of Geology and Mineral Resources, “Sinkholes and Karst Terrain.” (visit link)
Virginia Department of Conservation and Recreation, “Coastal Plain Depression Swamps and Ponds.” (visit link)
Richard K. Myers, Sandra Y. Erdle, Natural Heritage Technical Report 04-05, “Seasonal Pond Natural Area Management Plan, Colonial National Historical Park,” Virginia Department of Conservation and Recreation, Division of Natural Heritage, July 2005. (visit link)
This earthcache was published with the permission of Newport News Park, and a geocache permit is on file.
Additional Hints
(Decrypt)
[To log this earthcache, send us a message or an email and copy and paste these questions, along with your answers. Please *DO NOT* post the answers in your log, even if encrypted. There's no need to wait for confirmation from us before you log, but we will reply to messages and to emails if you include your email address. Group answers are fine; just let us know who was with you.
1. The name of this earthcache: Grafton Ponds Earthcache
2. In your own words, how did the sinkholes form?
3. Describe the pond at the listed coordinates. Based on your observations, do you think this pond at the coordinates holds water year-round? Why or why not?
4. (Optional) Compare the pond at the listed coordinates to one or both of the ponds at the additional waypoints. Do you think this second pond (or these other two ponds) hold water year round? Why or why not?
Photos of your visit are optional but highly encouraged and greatly appreciated.]
Treasures
You'll collect a digital Treasure from one of these collections when you find and log this geocache:
Loading Treasures