Inland Dunes
Dunes are a very rare geologic phenomenon away from the coast in New England. In New Hampshire, the only inland dunes occurs in the high terraces associated with the broad meanders of the upper Merrimack River in Canterbury. These terraces have been periodically scoured during major flood events, burying the point bars with fresh sand and gravel deposits. Subsequent re-working of sand deposits by wind has formed dunes on portions of these plains.
How Did The Sand Get Here?
The bottomlands along this part of the upper Merrimack River consist of glacio-lacustrine deposits (lake-bed and river delta sediments) associated with glacial Lake Merrimack, which existed between 14,300 to 14,750 years ago. Thinly-bedded, alternating layers of silt and clay lake-bed deposits (called “varves”) were covered by river delta deposits, which were in turn capped by deep fluvial deposits of more recent origin that eventually filled Lake Merrimack.
For a full discussion of how these deposits occurred, please see the nearby Earthcache, Varves at Muchyedo Bluffs (GC60W8Z)
After glacial Lake Merrimack filled in, the river cut its way through about 25 m of these deposits to reach its present day level, maintaining a series of broad, sandy peninsulas that support this and other communities. During the post-glacial time, flood and fire dynamics have been operating on these riverwash plains. Periodic scouring during major flood events buried the plains with fresh sand and gravel deposits. Subsequent re-working of sand deposits by wind has formed dunes on portions of the plains. The earthcache brings you to the two largest examples of this community.
Floodplains supporting this community range from unvegetated to wooded, depending on the degree of natural and human disturbance. This community can include woodland pockets surrounded by areas of open sand, but does not include extensive forested areas on these floodplains. Open areas support a sparse to moderate cover of drought-tolerant grasses, sedges, forbs, and a cryptogamic crust (some combination of mosses, lichens, fungi, bacteria, and algae). Shrubs and tree saplings are widely scattered overall, but are more abundant at the community margins.
Logging Requirements:
1. At the posted coordinates, please describe your surroundings with specific emphasis on the sediments under your feet.
2. Is the area at the posted coordinates open or wooded? Based on the cache page, please explain how you think it got to be open or wooded.
3. At the reference point, please take an elevation and compare to the elevation at the posted coordinates. Estimate the height of the dunes. Can you find an example of a higher dune in this area? Are you impressed or is it Muchyedo about nothing? Was it worth the bushwack?
Reference:
Sperduto, D.D. and William F. Nichols. 2011. Natural Communities of New Hampshire. 2nd Ed. NH Natural Heritage Bureau, Concord, NH. Pub. UNH Cooperative Extension, Durham, NH. © 2011, 2005, 2004 by the New Hampshire Natural Heritage Bureau. All rights reserved.