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 Geoform 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, 2012

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

Channel

Delta or fan

Delta or fan

DEEP INFRALITTORAL: 5 m–30 m water depth

Wall

Delta or fan

Floor

SHALLOW INFRALITTORAL: 0 m–5 m water depth

LIST OF MAP UNITS

Floor

Moraine

Rock outcrop or wall

Slump

Delta or fan

Floor

Moraine

Rock outcrop or wall

Slump

Moraine

CIRCALITTORAL (OFFSHORE): 80 m–200 m water depth

CIRCALITTORAL: 30 m–80 m water depth

Slump

Floor

Moraine

Rock outcrop or wall

Channel

MESOBENTHIC: 200 m–1,000 m water depth

Delta or fan

Floor

Moraine

Rock outcrop or wall

Slump

Scientific Investigations Map 3253

Sheet 4 of 4

Pamphlet accompanies map

U.S. Department of the Interior

U.S. Geological Survey

Discussion

 This map shows the primary morphologic features within West Arm, Glacier 

Bay National Park & Preserve, Alaska. The Coastal and Marine Ecological Classification Standard (CMECS, Madden and others, 2009) by the National Oceanic and 

Atmospheric Administration (NOAA) and NatureServe was used to classify various 

submarine landforms. Geoforms were manually selected from the multibeam 

bathymetry with the aid of video observations, seismic reflection profiles, bottom 

grab descriptions, knowledge of glacimarine processes, well-documented glacial 

history in the West Arm, and interpretations from other studies (for example, Cai 

1994).

 Units displayed on this map represent the geoform component of the 

CMECS classification draped over the shaded-relief multibeam bathymetry. Geoforms shape the seascape and provide structure and channel energy, regulate 

bioenergetics, and control transfer rates of energy, material, and organisms 

(Madden and others, 2009). Geoforms are defined based on spatial scales ranging 

from megageoform (largest) to microgeoform (smallest). All units depicted in this 

map are mesogeoform scale, as they range in size from tens of meters to kilometers. All geoforms displayed are part of the megageoforms of continental margin 

and fjord. Smaller-scale landforms within the mesogeoform scale exist within the 

map units, including channel, slump, rock outcrop, and fan. Each geoform is divided 

into its respective CMECS benthic depth zone: 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). Bathymetric contours represent the divisions between 

these depth zones. As water depth increases, the shade of color for each geoform 

darkens. 

 Deltas depicted are both fluvial and fully glacifluvial in origin and most are 

at least partially fed by glacial meltwater runoff. Morainal forms include kame 

terraces, morainal banks, push moraines, and complexes composed of multiple 

superimposed features, which formed in contact with and proximal to the terminus. 

Lithologically heterogenous, morainal banks are composed of poorly sorted sand 

and gravel, weakly stratified to massive diamicton, and stratified sand and mud. 

Seismic reflection profiles indicate that many of the prominent morainal banks within 

the West Arm are cored by bedrock and are therefore sills (Cai, 1994). Relict 

moraines are typically draped in distal mud, except where high-energy processes 

disrupt hemiplegic sedimentation, as in the tidally winnowed shallows of Hugh Miller 

Inlet. Similarly, rock outcrop and wall classes imply that the underlying morphology 

of the feature is bedrock controlled; however, owing to the large influx of glaciallysourced mud, even steeply-sloping bedrock features may have an extensive mud 

 drape. (See the accompanying pamphlet for a more detailed discussion of substrate

 relations for each geoform.) 

137°0' 136°30' 136°0' 135°30' 135°0'

59°0'

58°30'

58°0'

Pacific

Ocean

Glacier

Bay Sheet 2

Location map showing CMECS geoform component maps 

of lower West Arm (sheet 2, black) and upper West Arm (this 

map, red), Glacier Bay National Park and Preserves, Alaska.

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/.

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'

59°5'

59°5'

59°0'

59°0'

58°55'

58°55'

58°50'

58°50'

Inlet

Inlet

Johns

Hopkins

Tarr

View 2. Perspective view looking northwest over the morainal bank that divides the basins of the upper and lower West Arm. The head of Tarr Inlet 

and Jaw Point of Johns Hopkins Inlet are visible in the background. While the precise age of this morainal bank is unknown, observational evidence 

constrains the date of deposition to sometime between 1860 and 1879. Based on predicted retreat rates, the terminus probably occupied this 

position during the middle to late 1870s. Given the rapid retreat rates characterizing this interval, it is unlikely that the terminus persisted at this 

location for more than a few years. At present, this sill is the primary bathymetric barrier between the lower West and upper West Arm. The ridgelike structures across the up-fjord side may be annual push moraines, formed by the temporary wintertime advances of the terminus. Visible in the 

 background are morainal and ice-contact deposits exposed near the mouths of Tarr and Johns Hopkins Inlets. These features are associated with a

 brief interval of quasi-stability, which occurred as the ice retreated from the main trunk of the West Arm. Following this interval, the termini in Tarr

 and Johns Hopkins Inlets have moved asynchronously to their modern positions. Vertical exaggeration in the perspective view, X1.5

View 1. Perspective view looking north over the termini of Margerie and Grand Pacific Glaciers at the head of Tarr Inlet, one of the largest tributary 

inlets with active tidewater termini in Glacier Bay. Sediment accumulations rates in Tarr Inlet are some of the highest in the world, averaging more 

than 4 m/yr near the head of the fjord, and decreasing to about 0.2 m/yr at the mouth (this study). The bulk of sediment is delivered by the lateral 

meltwater streams that discharge along both sides of the two glaciers. The submarine channel that originates along the steep unconsolidated slopes 

of the fjord-head deltas and morainal banks, has been traced roughly 8km down Tarr Inlet (Cai and others, 1997). The Tarr basin has been infilling 

since the terminus retreated from the mouth of the inlet in the 1890s. Historically, sediment entering the basin has been confined by the relict 

morainal bank at the mouth of the inlet. The 2009 bathymetry indicates that this morainal bank may be approaching its capacity as a sediment trap, 

forcing excess sediment to bypass Tarr Inlet. At present, the bypassing sediment constitutes a small fraction of the total sediment entering Tarr; 

however as more efficient pathways evolve, a second depocenter may develop at the mouth of the inlet. Vertical exaggeration in the perspective 

view, X1.5.

2

1

1 Department of Geology and Environmental Geosciences, Northern 

Illinois University

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