The earthcache is located within Salisbury Beach State Reservation. The beach is open from dawn to dusk; night caching is not allowed. The Reservation is a Massachusetts DCR facility so there is a day use entrance fee between Memorial Day weekend and Labor Day and on weekends between Labor Day and Columbus Day.
This is an earthcache so there isn’t a container to find but instead you discover something about the geology of the area. To log this cache as a found, you will view the location at low tide and then provide answers to a few questions. Note, this earthcache can only be done at low tide because the earthcache location is covered by water at any other time. Here is a link to the local tide chart.
Salisbury Marsh
The Salisbury Marsh is part of what is called the Great Marsh. The Great Marsh is the largest, continuous salt marsh in New England. This wetland ecosystem extends from Cape Ann to the New Hampshire border and includes not just salt marsh but also barrier-island beaches, tidal creeks and rivers. At more than 20,000 acres, it is recognized as vital habitat for migratory waterfowl, shorebirds and endangered species such as piping plovers.
Salt Marsh Formation
Glaciers scoured the Northern Massachusetts coast between 22,000 and 12,000 years ago. The observed stratigraphy is evidence of a gradual marine transgression and rising sea-level since about 6300 B.P. The blue clay was deposited during late Pleistocene in an estuarine area at or near sea level. By 10,500 years B.P., the ice had retreated and the land was rebounding more rapidly than sea level was rising. About 7500 B.P. the land reached its maximum uplift while sea level reached maximum regression. By 6300 B.P. the land began to subside and the sea started infringing over the glaciomarine blue clay (i.e., an environment containing both glacial ice and marine water). At about 3000 years B.P., a marked decrease in the rate of sea-level rise occurred along much of the New England coast. Since then sea-level appears to have remained stationary.
Salt marshes form on parts of the coast that are protected from the full force of the waves by barrier islands and estuaries. The Salisbury Marsh is protected from waves by Salisbury beach which is a barrier beach. In many of the protected areas of the coast mud, silt and clay sediments settled out of the water to form extensive mud flats. Twice a day at low tide, portions of these mud flats are exposed to open air. Seeds from two grasses, Smooth Cordgrass (Spartina alterniflora) and Salt Marsh Hay (Spartina patens) took root in the mud. Both species possess a special regulatory system to excrete excess salt through pores in their leaves. As grasses sprouted and spread asexually through underground rhizomes, the thick growth began to trap more sediments and organic matter which raised the level of the marsh. The organic matter and dead spartina grasses accumulate underneath the new growth as peat.
In the Salisbury Marsh, a belt of peat 3-4M thick extends from the northeast across most of the marsh, nearly parallel to a series of bedrock pinnacles in the northwest. Looking at the stratification on the exposed bank, you will see the general overlapping stratigraphy of black peat overlain by the intertidal facies and the Smooth Cordgrass to Salt Marsh Hay sequence. The presence of the silty to sandy intertidal facies under most of the Smooth Cordgrass peat suggest that the latter did not develop until the sand- and mud-flats of the former open bay environment built up to mid-tide level about 3000 B.P.
Salt Marsh Zonation
Smooth Cordgrass is more effective at disposing of excess salt and can better tolerate having its roots submerged by the daily tides. At higher levels of the marsh which are only exposed to the highest tides, Salt Marsh Hay outcompetes Smooth Cordgrass and becomes the dominant species. This interaction with the tides creates vertical zones with a Low Marsh consisting almost exclusively of Smooth Cordgrass at the ocean’s edge and a High Marsh consisting of Salt Marsh Hay and other salt tolerant species.
Salt Marsh Changes
Marshes undergo constant change as they respond to both the daily tides and biological processes; tidal flooding supplies marshes with sediment, while the grass plants help to trap sediment and build peat through the input of organic matter. As average water levels rise, the potential for sediments suspended by flooding tides to deposit on the marsh increases, and the potential for peat to dry out and oxidize decreases. Over time this deposited sediment, combined with accumulation of organic matter leads to elevation gains on the marsh surface.
Another important mechanism for sediment deposition in northern marshes is ice rafting. Ice rafting is the transport of various materials by ice. Deposition through ice rafting occurs when ice forms and freezes to exposed mudflats at low tide, and the rising tide transports the ice sheets to the adjacent marsh, along with mudflat sediment attached to the bottom of the ice. When the ice melts, any sediment contained within or beneath the ice is left on the marsh surface. This process can be repeated throughout the winter, resulting in small patches of sediment accumulation on the marsh surface, sometimes as multiple layers.
Earthcache Questions
To get credit for this earthcache, you will need to send to me the answers to the following questions by email or Message Center. Please include the name of the earthcache in your message. You don't have to wait for a response from me after you send the answers.
Reminder: this earthcache can only be done at low tide.
- Look at the stratification (i.e., layering) in the exposed banking on the opposite side of the creek.
a) How many different layers can be seen in the banking?
b) For each layer, provide an estimate of its thickness, color, and consistency.
c) Why do the layers have the thickness they have?
- Observe the grass on top of the banking. Which type of grass do you think it is and why?
- Do you think the marsh is growing, staying the same or receding? Explain why.
- Include a photo of you/GPS standing at ground zero.