New Hampshire Shelf

High-Resolution Bathymetry, Surficial Geology Maps and Interactive Databases: Continental Shelf from Coastal New Hampshire to Jeffreys Ledge

CONTACTS: Paul Johnson and Larry Ward

DISCLAIMER: All information provided here is for displaying seafloor properties and cannot be used for navigation purposes.

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Interactive Compilation
 

Use of Maps and Database

The information provided here is freely available for use. However, the University of New Hampshire (UNH) Joint Hydrographic Center/Center for Coastal and Ocean Mapping (JHC/CCOM) should be acknowledged.

Recommended Citation

Ward, L.G., McAvoy, Z.S., Johnson, P. and Morrison, R. 2021, High-Resolution Bathymetry, Surficial Geology Maps and Interactive Databases: Continental Shelf from Coastal New Hampshire to Jeffreys Ledge, University of New Hampshire Center for Coastal and Ocean Mapping and Joint Hydrographic Center, Durham.
https://gis.ccom.unh.edu/portal/apps/instant/sidebar/index.html?appid=ecfea7ecddb04db49d9b75b676663925

Map Coordinate System, Projection and Datum

Coordinate System: WGS 1984 UTM Zone 19N

Projection: Transverse Mercator

Horizontal Datum: WGS 1984; Vertical Datum: MLLW

In Memoriam

Maxlimer Coromoto Vallee-Anziani was a valued colleague and a major contributor to the original work of developing the surficial geology maps, databases, and geological interpretations of the New Hampshire continental shelf. Sadly, Maxlimer passed away on January 24, 2017. However, her contributions both as a colleague and as a friend are not forgotten and will always be appreciated.

Overview

The continental shelf off New Hampshire (NH) in the Western Gulf of Maine (WGOM) is extremely complex and includes extensive bedrock outcrops, marine-modified glacial deposits, marine-formed shoals, seafloor plains, and associated features composed of a range of sediment from mud to gravel. The physiography and composition of the seafloor often changes dramatically over relatively short distances (tens of meters). The complexity of the WGOM seafloor results from the interplay of glaciations, sea-level fluctuations, and marine processes (waves and currents).

High-resolution multibeam echosounder (MBES) bathymetry and backscatter surveys, along with ground truth consisting of archived seismic reflection profiles, bottom sediment grain size data, vibracores, and video were used to develop surficial geology maps based on the Coastal and Marine Ecological Classification Standard (CMECS; FGDC 2012).

  Map of continental shelf off NH.
 
Figure 1. Geoform map for the continental shelf off the coast of New Hampshire to Jeffreys Ledge.
   
   
  Geoform map of the inner continental shelf off NH.
 
Figure 2. Geoform map for the inner continental shelf off the coast of New Hampshire.
   
   
 
 
Figure 3. Surficial sediment map based on CMECS showing the substrate groups for the continental shelf off New Hampshire.
   
   
  Map of continental shelf off NH.
 
Figure 4. Station locations for the 2016-2018 NH shelf field campaign.
   
   
 
 
Figure 5. Station locations for the NH Shelf Historical Database.
   

The surficial geology maps cover an area of ~3,250 km2 that extends from the coast of NH seaward ~50 km to Jeffreys Ledge and depict major geoforms (physiographic features) and seafloor substrate (sediment size) classifications (Figure 1). Presented here are the high-resolution surficial geology maps and an interactive database that includes seafloor photographs and bottom sediment grain size data from a major field campaign in 2016 and 2017, an historical sediment grain size database, and vibracore logs.

The new surficial geology maps depict the exposed bedrock, morphologic features, and sediment distribution in exceptional detail, revealing features of the seafloor that were not previously described. These maps, first presented in 2016 and updated and refined in 2021, are the most detailed to be published for the inner continental shelf off New Hampshire. The databases and the methods utilized to map the surficial geology of the NH continental shelf are described in detail in Ward et al. (2021a).


Surficial Geology Maps

Geoforms, as identified here and based on an adaption of CMECS, are morphologic features that are formed by geologic processes. For example, relatively large features with positive relief such as exposed bedrock, drumlins, moraines, or sand shoals would be considered geoforms. Also, low lying features are included as geoforms such as flat or low-slope seafloor plains, sand ramps, or small channels on the seafloor. The main geoforms identified in the study area are defined in Table 1 and shown in Figures 1 and 2.

The CMECS geologic substrate classifications are built on a simplification of the Wentworth (1922) and Folk (1980) classification schemes (Table 2). Essentially, the size classes are grouped into a hierarchy of broader categories including Substrate Class, Substrate Group, and Substrate Subgroup. Each level provides more detail of sediment classification (Figure 3). 


NH Shelf Seafloor Sediment Field Campaign Database: 2016-2017

A major field campaign was conducted in 2016–2017 on the NH continental shelf to obtain accurately located sediment samples and seafloor images (Figures 4). At eighty-five of these stations, bottom sediment was collected and grain size determined using standard sieve and pipette analyses (after Folk 1980). Statistics were determined in Gradistat (Blot and Pye, 2001) and classified using CMECS (described below).


NH Shelf Historical Geophysical Database: 1971-2015

A database built from previous studies conducted by UNH scientists on the NH continental shelf from 1971 to 2016 includes sediment grain size statistics from ~750 seafloor samples taken with a variety of instruments including grab samplers, box corers and vibracores (Figure 5). Although the archived database is relatively large, the coverage is inconsistent in quality and distribution. Therefore, the uncertainty of sample locations was evaluated for each sample and included in the database. Also included in the geophysical database are descriptive logs from twenty-three vibracores taken on the NH continental shelf in 1984 and 1988 by Birch (1984). The vibracores are described in detail in Ward et al. (2021b).

Data Access

A detailed report and all of the data and photographs found in this web site are available digitally from the following sources.

  1. Surficial Geology of the Continental Shelf off New Hampshire: Morphologic Features and Surficial Sediment: BOEM/New Hampshire Cooperative Agreement (Contract M14ACOOO10) Technical Report, Department of Interior, Bureau of Ocean Energy Management, Marine Minerals Division, 45600 Woodland Road, Sterling, VA, 20166, 184pp. https://dx.doi.org/10.34051/p/2021.31
     
  2. New Hampshire Continental Shelf Geophysical Database: 2016-2017 Field Campaign Seafloor and Sample Photographs and Sediment Data  https://dx.doi.org/10.34051/d/2021.1
     
  3. New Hampshire Continental Shelf Geophysical Database:  2016-2017 Field Campaign Stations and Sediment Data https://dx.doi.org/10.34051/d/2021.2
     
  4. The New Hampshire Continental Shelf Geophysical Database: 2016-2017 Field Campaign Seafloor Photographs https://dx.doi.org/10.34051/d/2021.5
     
  5. The New Hampshire Continental Shelf Historical Geophysical Database: 1971 to 2015 Sediment Data https://dx.doi.org/10.34051/d/2021.3

The report and databases presented here are part of a comprehensive series of reports on the bathymetry and surficial geology of the continental shelf off New Hampshire developed and supported by BOEM and UNH JHC/CCOM. Other associated major reports include the following.

  1. Ward, L.G., McAvoy, Z.S., and Vallee-Anziani, M., 2021a, New Hampshire and Vicinity Continental Shelf: Sand and Gravel Resources: BOEM/New Hampshire Cooperative Agreement (Contract M14ACOOO10) Technical Report, BOEM Marine Minerals Branch, 381 Elden Street, Herndon, VA, 20170, 97 pp.
    https://dx.doi.org/10.34051/p/2021.30
     
  2. Ward, L.G., Morrison, R.C., McAvoy, Z.S., and Vallee-Anziani, M., 2021g, Analysis of Vibracores from the New Hampshire Continental Shelf from 1984 and 1988: BOEM/New Hampshire Cooperative Agreement (Contract M14AC00010) Technical Report, Department of Interior, Bureau of Ocean Energy Management, Marine Minerals Division, 45600 Woodland Road, Sterling, VA, 20166, 173 pp. 
    https://dx.doi.org/10.34051/p/2021.26
     
  3. Ward, L.G., Johnson, P., Bogonko, M., McAvoy, Z.S., and Morrison, R.C., 2021h, Northeast Bathymetry and Backscatter Compilation: Western Gulf of Maine, Southern New England, and Long Island Sound:  BOEM/New Hampshire Cooperative Agreement (Contract M14ACOOO10) Technical Report, Department of Interior, Bureau of Ocean Energy Management, Marine Minerals Division, 45600 Woodland Road, Sterling, VA, 20166., 23 pp. https://dx.doi.org/10.34051/p/2021.28
     

Additional Databases and Surficial Geology Maps of the Continental Shelf off NH

Other web pages showing bathymetry, backscatter, surficial geology maps, photographs, bottom sediment data can be found at the University of New Hampshire (UNH) Center web site (http://ccom.unh.edu/) including:

High Resolution Seafloor Surficial Geology Maps and Interactive Database: Jeffreys Ledge and Vicinity http://ccom.unh.edu/project/jeffreys-ledge;

Northeastern Bathymetry and Backscatter Compilation: Western Gulf of Maine, Southern New England and Long Island http://ccom.unh.edu/project/NE-bathymetry-and-backscatter-compilation.

Acknowledgements

The development of the surficial geology maps and associated products was supported by the University of New Hampshire/National Oceanic and Atmospheric Administration Joint Hydrographic Center Award Number NA15NOS4000200 and the Bureau of Ocean Energy Management Award Number M14AC00010. A number of colleagues at the CCOM/JHC provided scientific and technical support, advice, and insight including Colleen Mitchell (Graphics Design and Editing), Will Fessenden (IT Group), and Larry Mayer, Giuseppe Masetti, Michael Bogonko, and Erin Nagel (Faculty and Research Scientists).

Cited References

Barnhardt, W.A., Andrews, B.D., Ackerman, S.D., Baldwin, W.E., and Hein, C.J., 2007, High-resolution geologic mapping of the inner continental shelf: Cape Ann to Salisbury Beach, Massachusetts: U.S. Geological Survey Open-file Report 2007-1373, variously paged. Accessed May 2019, available online at http://pubs.usgs.gov/of/2007/1373/

Birch, F.S., 1984, A geophysical study of sedimentary deposits on the inner continental shelf of New Hampshire: Northeastern Geology, volume 6, number 4, pp. 207-221.

Blott, S.J. and Pye, K., 2001, Gradistat: A grain size distribution and statistics package for analysis of unconsolidated sediments.  Earth Surface Processes and Landforms, v.26, no. 11, p.1237-1248.  http://dx.doi.org/10.1002/esp.261

FGDC (Federal Geographic Data Committee, Marine and Coastal Spatial Data Subcommittee), 2012, Coastal and Marine ecological classification standard, FGDC-STD-018-2012, Washington, DC, 343 pp., https://www.fgdc.gov/standards/projects/cmecs-folder/CMECS_Version_06-20...

Folk, R.L., 1980, Petrology of Sedimentary Rocks: Hemphill Publishing Company, Austin, TX. 182 pp.

Ward, L.G., McAvoy, Z.S., Vallee-Anziani, M., and Morrison, R.C., 2021a, Surficial Geology of the Continental Shelf off New Hampshire: Morphologic Features and Surficial Sediment: BOEM/New Hampshire Cooperative Agreement (Contract M14ACOOO10) Technical Report, Department of Interior, Bureau of Ocean Energy Management, Marine Minerals Division, 45600 Woodland Road, Sterling, VA, 20166, 184pp. https://dx.doi.org/10.34051/p/2021.31

Ward, L.G., Morrison, R.C., McAvoy, Z.S., and Vallee-Anziani, M., 2021b, Analysis of Vibracores from the New Hampshire Continental Shelf from 1984 and 1988: BOEM/New Hampshire Cooperative Agreement (Contract M14AC00010) Technical Report, Department of Interior, Bureau of Ocean Energy Management, Marine Minerals Division, 45600 Woodland Road, Sterling, VA, 20166, 173 pp. https://dx.doi.org/10.34051/p/2021.26

Ward, L.G., Johnson, P., Bogonko, M., McAvoy, Z.S., and Morrison, R.C., 2021c, Northeast Bathymetry and Backscatter Compilation: Western Gulf of Maine, Southern New England, and Long Island Sound: BOEM/New Hampshire Cooperative Agreement (Contract M14ACOOO10) Technical Report, Department of Interior, Bureau of Ocean Energy Management, Marine Minerals Division, 45600 Woodland Road, Sterling, VA, 20166., 23 pp. https://dx.doi.org/10.34051/p/2021.28

Wentworth, C., 1922, A scale of grade and class terms for clastic sediments: The Journal of Geology, v. 30, no. 5, p. 377–392. Accessed May 2019, available online at https://www.jstor.org/stable/30063207

 

Table 1(a). Geoforms classification modified after FGDC (2012).
 
  • Bedforms or Bedform Field: Area of larger bedforms or subaqueous dunes that are identifiable with bathymetry, hillshade, and backscatter. Thus, they must have wavelengths that exceed the bathymetry grid size. They are assumed to be largely composed of sand or gravelly sand and are formed by waves and currents.
  • Bedrock Border: Deposit of unconsolidated sediment surrounding a bedrock outcrop. They are identified by bathymetry, hillshade, roughness, and acoustic backscatter.
  • Channel: Linear or sinuous depression on an otherwise flat seafloor.
  • Depression: Small, shallow basin or low areas of the seafloor with no natural outlet. Depressions are identified by bathymetry, BPI, and hillshade.
  • Ebb Tidal Delta: Subaqueous, typically fan-shaped delta composed of mostly sand and fine gravel located on the seaward side of a tidal inlet. The morphology of these features is controlled by the flood and ebb tidal currents through the adjacent tidal inlet.
  • Iceberg Scour Scar: Gouges or deformation of the bottom formed by movements of an iceberg dragging across the substrate. They are formed in glaciated areas and can extend for long distances.
  • Inlet: Narrow opening in the coast that facilitates water exchange between the ocean and adjacent enclosed bays, lagoons or marshes.
  • Moraine: Elongated mound or ridge-like feature often occurring as clusters on sloping seafloor or imposed on bathymetric features with positive relief. These distinct subglacial deposits are composed of unsorted, unstratified gravel mixes to megaclasts.
  • Ridge: Elongated, narrow, steep-sided, crested feature. Identifiable in bathymetry and shaded relief.
  • Shoal: Relatively shallow area in a body of water, rising above adjacent seafloor. Shoals are morphologically diverse and are largely influenced by tidal or river currents. Shoals are normally composed of sand but can also be gravel mixes.
  • Slope: An inclined area of seafloor with a gentle change in depth over its upper and lower limits. Slopes occur at all scales and can be composed of various types of material. Primarily identified by bathymetry.
  • Tombolo: Sand or gravel bar or barrier that connects an island with the mainland.
 

 
Table 1(b). Geoforms classification modified after Barnhardt et al. (2007).
 
  • Nearshore Ramp: Gently sloping sandy or gravelly seafloor located offshore of a beach. The nearshore ramp generally exhibits shore-parallel bathymetric contours and is primarily covered with sand-rich sediment, although locally small exposures of ledge, cobbles, and boulders may be present.
 

 
Table 1(c). Geoforms classification defined for this study (Ward et al. 2021a).
 
  • Bedrock Outcrop: Exposed bedrock with little sediment coverage. It is often heavily vegetated. Bedrock outcrops are identified by bathymetry, hillshade, roughness, and acoustic backscatter. The bedrock often has ridges separated by bathymetric lows or swales with sediment.
  • Marine-Formed Feature or Shoal: Wave- or current-formed features such as sand bars or mounds, shoals formed at lower sea levels but now submerged, and sand or gravel ridges. The marine-formed features tend to have relief but are generally smooth in appearance. Although defined here, the features are similar in some cases to moraine shoals or other drowned, elongated offshore ridges. 
  • Marine-Modified Glacial Feature: Glacially formed feature3 now submerged and altered via erosion in the marine environment. Examples include eroded drumlins, eskers, outwash, or moraines (see Glossary). In the study area, the drumlins tend to be 0.5 - 4 km in length (long axis) and are oriented northwest-southeast. Some of the larger features (up to 10 km) appear to be groups of drumlins. Small glacial moraines also occur that are less than a few hundred meters in length, linear to arcuate in shape with low relief, and tend to be oriented in a northeast-southwest direction (likely De Geer moraines). Marine-modified glacial features tend to have high backscatter and roughness. The surface can appear eroded and rough, presumably due to the presence of cobble to boulder gravels.
  • Seafloor Plain: Large area of the seafloor that are relatively flat or have a low slope. They can have local areas that are undulating or slightly rougher than adjacent areas. Seafloor plains tend to be composed of finer-grained sediments. 
  • Sediment-Draped Bedrock: Bedrock covered by a thin layer of sediment. It appears as distinctive bedrock, but the texture is more subdued. 
  • Undefined: Apparent geoforms or areas of the seafloor which cannot be identified with the available database. 

 

Table 2. CMECS Sediment Classification (from FGDC, 2012).