Boston Harbor Islands National Recreation Area: Geologic resources inventory report
Thornberry-Ehrlich TL. 2017. Boston Harbor Islands National Recreation Area: Geologic resources inventory report. Natural Resource Report. NPS/NRSS/GRD/NRR—2017/1404. National Park Service. Fort Collins, Colorado
This report synthesizes discussions from a scoping meeting held in 2007 and a follow-up conference call in 2015 (Appendix A). Chapters of this report discuss the geologic setting, distinctive geologic features and processes within Boston Harbor Islands National Recreation Area, highlight geologic issues facing resource managers, describe the geologic history leading to the present-day landscape, and provide information about the previously completed GRI map data. Figures in Appendix B illustrate these data. The only drowned drumlin field in the United States is protected in the midst of Boston Harbor. These hills of mixed glacial sediment rest atop ancient bedrock that is part of a landmass once exotic to North America. Today, world class-coastal features attract geomorphologists to study the coastal processes at work at Boston Harbor Islands National Recreation Area. This study site has become a crucial place to investigate the potential impacts and responses to global climate change and resultant sea level rise. Authorized on 12 November 1996, Boston Harbor Islands National Recreational Area (also known as Boston Harbor Islands National and State Park) is a landmark effort among cooperating agencies and landowners working together through the Boston Harbor Islands Partnership. The National Park Service facilitates resource management and science in order to fulfill the purpose of the national recreation area as defined in its enabling legislation “to protect the drumlin archipelago in Boston Harbor and associated natural, geologic, cultural and historic resources.” The national recreation area encompasses 34 islands and former islands (now peninsulas) in Boston Harbor with more than 66 km (41 mi) of shoreline. Boston Harbor Islands are within an ancient geologic structure—the Boston Basin. This topographically low area in eastern Massachusetts began as an extension basin within a landmass that tectonic forces pushed and pulled across ancient seas before it was accreted onto the eastern margin of North America during the Paleozoic Era, more than 252 million years ago. The fault-bounded basin had collected sediments and volcanics (geologic map units CZca, Zdm, Zcr, Zvt, Zvm, and Zvp) more than 500 million years ago that would prove less resistant to erosion than the igneous and metamorphic rocks (e.g., Zgr and SOqgr) surrounding it. When glaciers scoured the landscape during the ice ages of the Pleistocene Epoch (2.6 million to 11,700 years ago), they carved the lowland of Boston Harbor, but also left vast amounts of sediment behind to form the “whaleback” mounds called drumlins. Some areas of bedrock persisted, particularly those underlain by intrusions of resistant igneous rocks (JZd, J[?]Zib, and J[?]Zdo; the question mark in the map unit symbols indicates uncertainty regarding the age assignment). When global sea level rose after glacial retreat, the drumlin field was eventually drowned, and coastal processes of wave erosion, longshore transport, and barrier migration began to shape the coastal features that persist at Boston Harbor Islands today. In general, the outer islands are smaller, rockier, and windswept, whereas the inner islands are generally larger and sandier, with forested areas.
- Type
- Published Report
- Authors
- Thornberry-Ehrlich, Trista
- Date of Issue
- 2017-03
- Publisher
- National Park Service
- Units
- BOHA , GRD , GRI , NETN , NRSS
- Keywords
- Abandoned Mineral Lands and Disturbed Lands, Aeolian Features and Processes, and Protection, Bedrock Exposures, Bluff Retreat, BOHA, Boston Harbor, Boston Harbor Islands National Recreation Area, Coastal Erosion and Response to Climate Change, Coastal Features, Faults, Folds, Geologic Features, Geologic Features and Processes, Geologic History, Geologic Processes, Geologic Resource Management Issues, Geologic Resources Division, Geologic Resources Inventory, Glacial Features, GRD, GRI, Loss of Aeolian Features, Map Units, Massachusetts, Monitoring, National Park Service, NPS, Paleontological Resource Inventory, Paleontological Resources, Resource Management, Sediment Supply and Island Erosion, Seismic Activity Hazards and Risks, Wetlands
- Subjects
- Ecological Framework: Geology and Soils | Geomorphology | Windblown Features and Processes , Ecological Framework: Geology and Soils | Geomorphology | Glacial Features and Processes , Ecological Framework: Geology and Soils | Geomorphology | Hillslope Features and Processes , Ecological Framework: Geology and Soils | Geomorphology | Coastal/Oceanographic Features and Processes , Ecological Framework: Geology and Soils | Subsurface Geologic Processes | Seismic Activity , Ecological Framework: Geology and Soils | Paleontology | Paleontology