• Stratified: exhibit layering
• Sorting: may be well to poorly-sorted, but most fines have been washed out and deposited downstream in a marine or lacustrine environment.

General definition: Any fluvial or related deposit (e.g. deltas) laid down within or against ice by glacial meltwater.

• General characteristics of ice-contact deposits:
  • Contains one or more steep ice-contact slopes
  • Typically exhibit collapse structures (normal faults and related folds formed by collapse of sediment when supporting ice is melted) 
  • Contains cruder stratification, and coarser, less well-sorted sediment than its distal proglacial counterparts. Ice contact deposits are generally a good source of gravel.
  • May contain lenses of flow till mass-wasted from the surface of disintegrating ice
• Ridge deposits
  • Eskers, crevasse fills, *subaqueous outwash ridge or delta ridges
    • Characteristics:
      • morphology: sinuous ridge; may be continuous for several km, discontinuous, or beaded; ridge crest is typically undulatory; eskers may traverse modern hydrologic divides (Waterford esker, Maine)
      • composition: Generally gravel and course sand; may contain flow till; sorting may range from well- to very poorly-sorted
      • Unique features: englacial and supraglacial eskers may be highly collapsed and exhibit slump folds and normal faults. Crevasse fills may have a deceiving cap of boulders or till mass-wasted onto the surface of the fluvial deposit.
      • *Subaqueous outwash/delta ridge is in fact not a true ice-contact deposit, but a ridge formed by a high pressure subglacial meltwater stream entering the ocean or a lake from the base of a glacier. It looks like an esker but lacks the flanking collapse features and is composed of dipping foreset beds.
      • orientation of eskers is governed by the pressure gradient (h/l) within the ice and are typically parallel to the direction of ice flow. 
• "Kames" : Another commonly used vague term. Generally, any ice-contact hill or deposit composed of stratified drift.
  • Kame terrace: terrace-like deposit formed where an esker producing stream flowed against a valley wall. A better term might be esker terrace. Kame terrace is also used to describe a terrace of outwash deposited against the ice margin.
  • Moulin kame: mound of fluvial debris deposited in a circular depression.
  • Kame outwash/delta: an outwash or deltaic deposit formed in direct contact with the glacier. Characterized by a steep ice-contact slope and more gently dipping downstream slope. Typically contains kettles, and is considered a type of moraine in the sense that it marks the position of the ice margin.
  • Kame and kettle topography: hummocky topography produced by the melting out of fluvial sediments deposited on marginal stagnant ice. Also called hummocky topography.

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  Glacial Fluvial Non-Ice Contact (Proglacial = beyond the front/paraglacial = way beyond the front)
  • Outwash: proglacial sand and/gravel deposited by braided streams
    • Sandur (outwash plain.) -- Broad outwash plain or delta. Remember that the upper surface of a delta is composed of fluvial outwash deposits.
    • valley sandur or valley train -- belt of outwash confined to a valley
  • Proglacial outwash is typically composed of braided stream deposits. Paraglacial outwash is deposited more often by meandering streams, which are less influence by the high sediment loads and extreme fluctuations in discharge experienced closer to the glacier.

   

   

• glacial lacustrine deltas: Typically Gilbert-type deltas (Composed of bottomset, foreset, and topset beds arranged in a coarsening-upward sequence.) The topset beds are commonly composed of gravel.
  • The topset/foreset contact marks the elevation of the water body to which the delta was graded.
• glacial lacustrine varves (bottomset beds): Graded beds resulting from seasonal variations in sedimentation rates.

 

How do glacial lakes form?

• debris dam lake
  • A lake dammed by a moraine or some other drift deposit
• Example:Glacial Lake Hitchcock in the Connecticut Valley was dammed by a delta deposit at Rocky Hill near Middletown Conn.)
• Ice dam lakes
  • A tongue or ice stream may block the natural drainage.
  • presence of ice results in local reversal of natural drainage and ponding of water along the ice margin.
    • Examples: Glacial Lake Agassiz and most of the outwash (deltas) that form Cape Cod.

 

• Notable ice-dammed lakes:
  • Glacial Lake Missoula, Montana: lake area = 500 sq. miles. Catastrophic releases of water carved the Channeled Scablands of Washington. Glacial lake Missoula formed repeatedly when a south flowing tongue of the Cordilleran Ice Sheet dammed the westward flowing Clark Fork River along the Idaho-Montana border.
  • Glacial Lake Agassiz; extended from Manitoba-Saskatchewan into Minnesota and the Dakotas; aggregate area = 312,500 mi2, but no more than 125,000 at one time. Isostatic depression produced a broad basin in which water became ponded against the retreating ice margin.
  • New England ice-dammed lakes:
    • Glacial Lake Cape Cod (discussion by Robert Oldale, USGS)
    • Glacial Lake Taunton (Ice dammed)
    • Glacial Lake Nashua (Ice dammed)
       

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Glacial Marine sediments

• glacial marine deltas:
  • Similar to glacial lacustrine deltas but contain massive bottomset beds
• subaqueous outwash:
  • Lacks topset beds and is commonly draped with younger marine clay. See also delta ridge above.
• glacial-marine clays (e.g. Map Presumpscot Formation, Introduction to the Presumpscot Formation, Maine's History of Sea Level Change - Maine Geological Survey Photo Gallery))

 Unlike lacustrine varve clays which are graded, marine clays are massive. Salt ions in sea water cause the clay to form curds (flocculate) that settle out with the coarser silt and fine sand.

 

The most extensive deposit of glacial-marine clay in New England occurs along the Maine coast where isostatic depression (about 600 feet) was enough to depress the land far below sea level. As the ice retreated the sea inundated lowlands and valleys until isostatic rebound forced it to retreat. The Presumpscot Formation (what they call the marine clay in Maine) is found up to 150 km inland of the coast at elevations of around 70 meters. In valleys and coastal lowlands it can be over 100 feet thick. Unlike most Quaternary deposits in New England the extent, thickness and known age of the Presumpscot makes it a distinct mappable unit and is therefore given formation status.

 

A similar marine clay, the Boston Blue clay, underlies Boston but does not extend above sea level. Boston marks the hinge line south of which isostatic depression was too little to cause a post glacial marine incursion. North of Boston the elevation of marine clay exposures in coastal regions increases to the north. (For more about the Boston blue clay see bigdig stratigraphy and how the clay came to pass) Here in Salem marine deposits are around 40-60 feet above sea level. (In fact the local White Hen Pantry and Video store on Loring Ave. is on a glacial-marine delta. --I was here when they dug the foundation.)

 

Glacial-marine clay can pose a number of engineering problems and is prone to liquefaction and landslide activity (Rockland Landslide-Maine Geological Survey Photo Gallery)). Thick deposits of clay along the Saint Lawrence an Ottawa valleys form the foundation for a number if deadly landslide that plague the region (Landslides in Clay). These clays were in part formed when a calving bay carved through the retreating ice sheet along the Saint Lawrence Valley.

depends on:

• Flow regime
  • Strength (see section below on bedforms)
  • Variability: flow regime will vary on a daily and seasonal basis 
• Sediment source
  • proximal and distal relationships
  • local variations: an esker by be flowing through a debris-rich band of ice
  • temporal variations: a sudden influx of coarse sediment may be introduced by a mass-wasting event 
• Depositional environment
  • Confined or unconfined channel
  • subaerial-terrestrial, subglacial, supraglacial, or subaqueous
  • marine or lacustrine
  • turbulent or quiet water 

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Bedforms

• Type of bedform is determined by
  • grain size, shape and density (fall velocity)
  • strength of flow (velocity)
  • depth of flow
  • sedimentation rate
  • unidirectional vs. bidirectional flow
  • depositional mechanism (traction, suspension, avalanching of grains, etc.) 

Glacial Lakes

• Glacial Lake Hitchcock
  • The Ice Age in Connecticut (Connecticut Geology)
  • Glacial Lake Hitchcock, (Tammy Marie Rittenour, Umass student)
  • Surficial Geology of the Danville/St. Johnsbury Area,Vermont by George M. Haselton and George Springston, Vermont Geological Survey
• Glacial Lake Agassiz
  • The Glacial Lake Agassiz, From Warren Upam's original monograph written in 1986
  • Glacial Lake Agassiz and the Red River Valley, Minn. Pollution Control Agency
  • Glacial Lake Agassiz by Edmund Sass, College of Saint Benedict/Saint Johns University
  • Lake Agassiz, A Child of Ice by Don McCollor, Earthscapes
• Glacial Lake Missoula
  • Glacial Lake Missoula, an ice age saga, Montana Natural History Center
• Midwest/Great Lakes
  • Gift of the Glaciers Glacial history of the Great Lakes
  • The Glacial Lakes Around Lake Michigan (PDF)
  • Glacial lakes and the Origin of Niagara Falls (Rick Berketa)

Deltas

• Pineo Ridge Moraine/Delta Complex in Eastern Maine, Colby College
• Glacial Marine delta terrace, Kentra Bay Baffin Island(images from Canadian Landscapes)
• Glacial outwash/delta/sandur, Labrador (images from Canadian Landscapes)

Eskers and Crevasse fills

• Eskers in Michigan, from the Geography of Michigan by Randal Schaetz, Michigan State Univ.
• multiridged esker, Manitoba, Esker Ridge, Manitoba, Sandy broad-crested Ridge, Manitoba, Esker ridge with side deltas, Manitoba (images from Canadian Landscapes)
• gravelly crevasse fills nw Manitoba, rectilineate crevasse fills Manitoba, Crevasse fill, Bylot Island (images from Canadian Landscapes)

Kame and kettle topography

• Kames and Kettles by William Locke, Glacial Geology
• Cape Cod Kettles (Nasa's Earth from Space), Glacial Cape Cod (Robert Oldale)

Outwash

• Outwash plains, from the Geography of Michigan by Randal Schaetz, Michigan State Univ.
• Geologic Origin of Stellwagan Bank (Robert Oldale)
• Glacial Cape Cod (Robert Oldale)

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Lindley Hanson (email) Last Modified 4/23/03