Cape Cod Landforms and Coastal Processes

Pilgrim Lake, once known as East Harbor, was open to Cape Cod Bay until a dike was built in 1869. High Head in Truro is a relic sea cliff that marks the northernmost edge of the glacial outwash de- posits on Cape Cod. A C P Race Point Light E

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Provincetown is built O primarily of sand eroded Pamet River is carved into the Wellfl eet glacial outwash plain creating the and transported from largest valley on Cape Cod. Pamet valley was possibly an outlet to a glacial D the Cape Cod National Highland Light lake that existed seaward (eastward) of Cape Cod. Seashore bluffs.

etween 18,000 to 25,000 years ago, sediment deposited by the advance, melting and re-advances of three major TRURO Wood End Light Long Point Light If not for Ballston Beach in Truro on the Atlantic Ocean, the Pamet glacial ice lobes, the Cape Cod Bay, Buzzards Bay, OUTWASH River would be a seaway making Truro and Provincetown an island. B N and South Channel Lobes, were responsible for the cre- PLAIN ation of the primary coastal landforms that make up Cape Cod today. A The glacial outwash plains of the Cape The most common glacial landforms on Cape Cod The 60-120 foot-high coastal bluffs along the Cape Cod Cod National Seashore are eroding 2.5 are end moraines, outwash plains, and kame and kettle Bay shores of Wellfl eet and to 3.5 feet per year and are over 150 terrain. Moraines generally contain unsorted, unstratifi ed Truro are the western extent T feet high and 15 miles long. They once clay, silt, sand, cobble, pebble, and boulders, collectively referred of glacial outwash deltas and extended seaward up to 4 miles when to as till. However, due to their mode of deposition, Cape Cod mo- plains laid down by the South laid down by the melting South Channel Plymouth’s 100-foot-high Ice Lobe some 20,000 years ago. raines contain stratifi ed deposits with a relatively thin cap of till. The Channel Ice Lobe. I eroding coastal bluffs are WELLF LEET portion of the Mid-Cape Highway (Route 6) that runs east-west and glacial outwash plains and parallel to the Cape Cod Bay shore was constructed on top of the Sand- moraines deposited by the O U T W A S H wich Moraine, deposited by advances of the Cape Cod Bay ice lobe. The Cape Cod Bay and Buzzards O portion of Route 28 that runs north-south and parallel to Buzzards Bay in the Bay Ice Lobes. Through PLAIN Towns of Bourne and Falmouth was constructed atop the Buzzards Bay Moraine. the process of longshore Bound Brook, Great and Griffi n Due to the curvature of the lower Cape and predominent Islands, and Great Beach Hill in northeast windward waves, a ‘nodal zone’ or divergence of As the Cape Cod Bay ice lobe melted and retreated northward, massive volumes sediment transport, they provide the primary source Wellfl eet are fl uvio-glacial kame N sand transport exists along the Wellfl eet shore that results of glacial melt-waters were trapped by the Sandwich Moraine and the glaciers and glacial of sand to Sandwich and deposits that were connected in sand being moved both north towards Provincetown and outwash plains to the east and west, creating Glacial Lake Cape Cod. Barnstable beaches. by sand spits or tombolos in south towards Chatham and Monomoy Island. The glacial lake’s highest surface elevation the early 1800s allowing the was approximately 80 feet above present sea growth of landward salt marsh. A level and its shoreline was positioned landward (south) of Route 6A in Sandwich, well inland of the

L Atlantic Ocean present Cape Cod Bay shore. Glacial Lake Cape Cod Billingsgate Island once supported 30 drained, perhaps catastrophically, through low areas Cape Cod Bay homes, a school and lighthouse. It was now occupied by the Cape Cod Canal, Bass River in Formerly Glacial Lake Cape Cod completely submerged in 1942 due to Yarmouth, and Town Cove in Orleans. relative sea level rise and a change in the EASTHAM Cape Cod beaches, dunes, and barrier beaches were longshore sand transport system. Nauset Lighthouse, threatened created from sediment originally eroded and transport- by the 2.5 to 3.5 feet per year O U T W A S H erosion rate, was moved land- ed from glacial landforms, such as moraines and out- In 1914 the Manomet S ward 300 feet in 1996. wash plains. This erosion was caused by winds, waves, River and Scusset Creek Revetments constructed PLAIN were widened and deep- tides, storms, and relative sea level rise. Today, Cape on eroding coastal banks Nauset Light ened to create the Cape Cod’s beaches, dunes and barrier beaches still depend protect landward develop- Cod Canal. While pro- Pile-supported dune walk- ment but reduce the major E on erosion and transport of sediment from these glacial viding safe navigation, ways minimize damage to source of sand to beaches In 1602, Gosnold referred to the outer deposits as their primary source of sediment and, thus, the Canal and adjoin- dune vegetation. Healthy and dunes contributing in- Cape as an island and a continuous their very existence. Cape Cod’s bays and estuaries ing jetties affect sand vegetation traps wind-blown stead to the narrowing, and channel was depicted on Captain were created by inundation of sea water into topographic lows as a result of relative sea level rise. Likewise, transport contributing to sand which adds to dune potential loss, of beaches. A Southhack’s 1717 map. This channel, saltmarshes eventually became established in these bays and estuaries, and landward of barrier beaches. beach erosion along the volume, thus enhancing Southward and eastward longshore called Jeremiahs Gutter, ran from west Sandwich shore. storm damage protection. sand transport systems converge Nauset Harbor to Town Cove through The ‘coastal landform systems’ of Cape Cod were thus established, and continue to provide storm damage along the Cape Cod Bay shore of the Orleans traffi c rotary and joined a protection, fl ood control, wildlife habitat, as well as recreational and aesthetic values. Beginning approximately 3,300 years Brewster to create extensive S tidal creek fl owing into Cape Cod Bay. Human actions, including the construction of seawalls, revetments, bulkheads, groins, and jet- ago, longshore sand transport from the exposed sand fl ats at low tide. This waterway may also have been an ties, along with buildings and landscaping, are now considered, in the short-term, on par with eroding Plymouth bluffs and Sandwich outlet for Glacial Lake Cape Cod. beaches formed Sandy Neck barrier beach. natural forces in controlling the shape and function of our shores and coastal landforms. Extensive salt marshes have since formed H There is a great need to understand how individual actions affect the sustain- behind the barrier beach, protecting the ability of coastal landform systems in order to mainland shore from storms. preserve Cape Cod, the gift of the glaciers, for

O In 1626 storms grounded the Sparrowhawk future generations. S A N D W IC H M O R A IN E onto shoals at Nauset Beach and washed it through an inlet into Pleasant Bay. In 1863, Arrows indicate direction of net 237 years later, the long forgotten wreck was longshore sediment transport.

R exposed on the ocean side of Nauset Beach. Beach Point Light The barrier beach continues its landward Produced and published by Cape Cod migration today. Cooperative Extension and the Woods

Hole Oceanographic Institution E Sea Grant Program. Project man- In 1605 Champlain drew a chart showing Nauset agement, text, and photographs Spit one-half mile seaward of its present location. for illustrations provided by Jim Storms and relative sea level rise are causing the O’Connell. Illustrations provided by HARWICH barrier beach to migrate landward an average of Dana Gaines. Design and production, 4-6 feet per year Jim Canavan, WHOI Graphic Services. Due to the Bay’s M O R A I N E Kettle Holes OUTWASH PLAIN References for source material orientation and Y on this poster can be found at: geometry, a 25- www.capecodextension.org and foot storm surge www.whoi.edu/seagrant. could inundate the northern M A S H P E E Chatham Light reaches of Buz- zards Bay under OUTWASH PLAIN Stage Harbor Light severe hurricane A northeast storm in January 1987 conditions. The combination of small tidal range (approximately breached Nauset Beach beginning 2.5 feet) and low wave energy a new cycle in the continuing evolu- makes the south side of Cape tion of the barrier beach. The breach Cod relatively calm with low elevated tides and caused erosion Bass River, deeply incised resulting in the loss of many homes BUZZARDS BA erosion rates. into glacial outwash, was along the mainland shore. likely an outlet for the Large boulders characterize catastrophic draining of Nearly two dozen harbors Buzzards Bay Moraine outcrops Glacial Lake Cape Cod. are scattered along Cape creating headlands along the Cod’s southern shores, most irregular Buzzards Bay shore- protected by double jetties. Popponesset Spit, a barrier beach, The southern half of Monomoy Island has been accreting line of Falmouth and Bourne, These jetties alter eastward has extended eastward several southeastward at a rate of about 25 feet per year since at coalescing with barrier beaches, sand transport, causing miles, then breached due to storms. least 1853, due in part to abundant sand coming from the saltmarshes, and embayments. downdrift erosion. The latest cycle began in the eroding cliffs of the Cape Cod National Seashore. 1950s when a series of hurricanes breached the barrier, overwashed, Buzzards Bay and its eastern section migrated and attached to the mainland. Waquoit Bay is a kettle Nobska Point is an ice-contact deposit formed hole that has been partly by the Buzzards Bay Ice Lobe. The bluff eroded submerged by the post- Monomoy Point Light nearly 50 feet during the 1938 Hurricane and glacial rise in sea level. has since been armored to protect Nobska Lighthouse, cutting off a signifi cant sediment PE CO supply to adjacent beaches. The harbors and ponds of southern Falmouth (Bournes, Nantucket Sound CA D Green, Great and Little Ponds and Falmouth Harbor) are

spring sapping valleys carved by glacial melt waters and C

O subsequently drowned by the post-glacial rise in sea level. N

O O P I E S Nobska Light N RA E TIVE EXT