Scientific Investigations Map 3253

Sheet 3 of 4

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey

137°0' 136°30' 136°0' 135°30' 135°0'

59°0'

58°30'

58°0'

Pacific

Ocean

Glacier

Bay

Sheet 1

Location map showing CMECS surface geology component 

maps of lower West Arm (sheet 1, black) and upper West Arm 

(this map, red), Glacier Bay National Park and Preserve, Alaska.

Sand

Bedrock

Boulder/rubble

CMECS SUBCLASS LEVEL: SURFACE GEOLOGY

Mixed

Mud

Cobble/gravel

Description

This map shows surficial sediment within the West Arm, Glacier Bay National Park and Preserve, Alaska, and was produced by manual polygon 

selection using geological reasoning, seafloor property measurements from the multibeam bathymetry, and knowledge of substrate types from 

video observations, seismic reflection profile interpretations, and sediment sampling. The sea floor properties examined during manual classification were rugosity (a dimensionless measure of seafloor roughness) and seafloor slope. These were used to help identify steeply sloping and 

rugose areas that are most likely bedrock or consolidated sediment. 

 The Coastal and Marine Ecological Classification Standard (CMECS, v. III, June 2009) by the National Oceanic and Atmospheric Administration (NOAA) and NatureServe was used to classify various substrate types (Madden and others, 2009). Units displayed on this map 

represent the surface geology component subclass level of the CMECS classification draped over the shaded bathymetry. Substrate distributions 

are summarized for the entire West Arm in the tables below. Table 1 shows the percent and area of the substrate distribution by CMECS class. 

The unconsolidated bottom CMECS class is divided into mud, mixed sediments, and cobble/gravel subclasses.The rock bottom CMECS class is 

divided into bedrock and boulder/rubble. Table 2 shows the substrate distribution across each benthic depth zone. Bathymetric contours represent 

the division between benthic depth zones as defined in CMECS. The zones depicted in this map are shallow infralittoral (0–5 m), deep infralittoral 

(5–30 m), circalittoral (30–80 m), circalittoral offshore (80–200 m), and mesobenthic (200–1,000 m). Substrate distribution within the shallow 

infralittoral (0–5 m) depth zone is included in table 2. However, due to coverage and resolution constraints, these values are conservative 

estimates. The bathymetric contour demarking the shallow infralittoral zone has been omitted for aesthetic reasons.

 Mud is the dominant substrate in the West Arm, comprising 72% or 277 km2

 (table 1), and the greatest abundance is in the mesobenthic 

depth zone (table 2). Abundant glacimarine mud in the West Arm is primarily sourced today from glaciers in Johns Hopkins, Tarr, and Queen Inlets. 

See the accompanying pamphlet for more information regarding sources and rates. Unclassified soft-bottom is the second most abundant 

substrate at 14.4% or 55.4 km2

, and the greatest percentage is located in the circalittoral and deep infralittoral depth zones. The unclassified 

soft-bottom subclass was applied to areas where ground-truthing coverage was poor, but higher-energy processes such as winnowing are 

suspected of disrupting hemipelagic deposition. Areas where no single size fraction constituted the majority of the substrate fall under the mixed 

sediments subclass. Mixed sediments comprise 1.6% or 6.2 km2

 and are primarily found in the shallows of Hugh Miller Inlet and at the mouth of 

Tidal Inlet where winnowing has exposed ice-contact sediments deposited during the post-Little Ice Age retreat of the Russell System. The sand 

subclass covers 3.0% or 11.8 km2

 and typifies the foresets of side-wall and fjord head deltas and active morainal banks. The latter environment 

likely includes a large component of other size fractions, reflecting depositional processes, including dumping and sediment gravity flows, yet it still 

conforms to the CMECS definition of the sand subclass. The cobble/gravel subclass, comprising 1.7% or 6.5 km2

 of the measured area in the West 

Arm, commonly occurs where high-gradient glacifluvial streams enter the fjord, such as along Johns Hopkins Inlet, or in tidally winnowed shallows 

as in Reid Inlet. Of the two rock bottom subclasses, bedrock was the most abundant, constituting 7% or 26.7 km2

 of the West Arm, or 98% of rock 

bottom substrates. Boulder/rubble could only be confidently mapped in 0.2% or 0.6 km2

, but likely contributes to the unclassified soft-bottom and 

bedrock subclasses in areas proximal to steep bedrock cliffs. 

Percent Area (km ) Percent Area (km ) Percent Area (km ) Percent Area (km ) Percent Area (km )

0.3 1.0 3.9 15.0 4.1 15.9 3.4 13.1 2.6 10.0

Mud 0.0 0.0 2.1 8.1 9.3 35.8 17.5 67.3 43.0 165.2

Sand 0.0 0.1 0.5 2.0 0.7 2.8 1.0 3.9 0.7 2.9

Mixed sediments 0.0 0.0 0.2 0.8 0.4 1.6 0.7 2.5 0.3 1.2

Cobble/gravel 0.1 0.3 0.5 1.9 0.2 0.8 0.3 1.1 0.6 2.4

Boulder/rubble 0.0 0.0 0.0 0.1 0.1 0.3 0.0 0.2 0.0 0.0

Bedrock 0.0 0.0 0.4 1.7 1.3 4.9 2.4 9.2 2.8 10.7

Shallow infralittoral

0–5 m water depth

Deep infralittoral

5–30 m water depth

Circalittoral 

30–80 m water depth

Circalittoral (o shore)

80–200 m water depth

Mesobenthic 

200–1,000m water depth

CMECS subclass 

Unclassi ed softbottom

Table 2. Substrate distribution vs. depth zone for the West Arm, Glacier Bay National Park and Preserve, Alaska.

CMECS class CMECS subclass

Unconsolidated bottom

Unclassi ed soft-bottom 14.4 55.4

Mud 72.0 276.6

Sand 3.0 11.8

Mixed sediments 1.6 6.2

Cobble/gravel 1.7 6.5

Rock bottom

Boulder/rubble 0.2 0.6

Bedrock 7.0 26.7

Percentage of 

total area Area (km )

Table 1. Substrate distribution in the West Arm, Glacier Bay National Park and 

Preserve, Alaska.

59°5'

59°5'

59°0'

59°0'

58°55'

58°55'

58°50'

58°50'

136°40'

136°40'

136°45'

136°45'

136°50'

136°50'

136°55'

136°55'

137°0'

137°0'

137°5'

137°5'

137°10'

137°10'

137°15'

137°15'

Inlet

Inlet

Johns

Hopkins

Tarr

MAP LOCATION

ALASKA

SCALE 1:50000

2 1 0 2 KILOMETERS

2000 0 2000 4000 6000 8000 10000 12000 14000 FEET

2 1 0 2 MILES

LAND CONTOUR INTERVAL 100 METERS

BATHYMETRIC CONTOURS: 30, 80, AND 200 METERS

SEA LEVEL, CYAN

CMECS Surface Geology Component Map of Upper West Arm, Glacier Bay National Park and Preserve, Alaska

By

Timothy O. Hodson1, Guy R. Cochrane2, Ross D. Powell1 

2013

APPROXIMATE MEAN

DECLINATION, 2013

21°

MAGNETIC NORTH

TRUE NORTH

Base from U.S. Geological Survey, National Elevation Dataset

NASA Landsat 7 Imagery, 1999

Universal Transverse Mercator Zone 8N Projection, WGS84

NOT INTENDED FOR NAVIGATIONAL USE

Manuscript approved for publication March 6, 2013

GIS database and digital cartography by 

T.O. Hodson 

Based on multibeam sonar data collected in

2009 during NOAA NOS hydrographic surveys 

H12140, H12141, and H12142

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the 

U.S. Government

This map was printed on an electronic plotter directly from digital files. Dimensional calibration may vary between electronic plotters 

and between X and Y directions on the same plotter, and paper may change size due to atmospheric conditions; therefore, scale and 

proportions may not be true on plots of this map.

For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225, 1–888–ASK–USGS

Digital files available at http://pubs.usgs.gov/sim/3253/

Suggested Citation: Hodson, T.O., Cochrane, G.R., and Powell, R.D., 2013, Marine Benthic Habitat Mapping of the West Arm, Glacier 

Bay National Park and Preserve, Alaska: U.S. Geological Survey Scientific Investigations Map 3253, pamphlet 30 p., scale 1:50,000, 

available at http://pubs.usgs.gov/sim/3253/.

1 Department of Geology and Environmental Geosciences, Northern 

Illinois University

Pacific Coastal and Marine Science Center, U.S. Geological Survey 2