ESKERS FROM ICE SHEETS

Eskers Show Where Ice Sheets Existed

ESKERS FROM THE ICE SHEETS

Eskers shown in red are rocky ridges that formed under the ice sheet. Moraines shown in green are where rocky “dams” formed at the ends of glaciers. Drumlins formed under the melting ice sheet, but are not shown here. Eskers are common in central and easter Canada, the northeastern U.S. and in Scandinavia in northern Europe.

ESKERS FROM IMPACTS?

Eskers show where the main ice sheet/s were located. Eskers were deposited by running water in cracks in the ice sheet/s. A thought that just occurred to me this morning (10/23/24) is that rock and soil could have gotten onto the surface of the ice sheet when large meteorites hit Michigan and maybe other places, like northern Greenland, and the impact explosions ejected rocks and soil onto the ice sheet. It's pretty certain that the impacts ejected ice boulders that formed the Carolina Bays and Nebraska rainwater basins, but there was likely some rock and soil also ejected. If that's the source of the esker sediments, the rocks should surely be angular like breccia instead of rounded. But no, Perplexity.ai gives me a different idea, which I'll discuss after these quotes. (Esker rocks are rounded, but Till, or Tillites, are angular, as is also the rocks in moraines.)

Rocks in eskers are typically rounded rather than angular1,3,4. Here's a more detailed explanation:
Characteristics of Esker Sediments
Eskers are ridges composed of glaciofluvial sediments, primarily sands and gravels, deposited by meltwater flowing through tunnels within or underneath glaciers1. The sediments in eskers have several key characteristics:
Roundness: The rocks and gravels in eskers are generally well-rounded to sub-rounded1,4. This rounding occurs due to the transport process:
As meltwater flows through glacial tunnels, it carries rock fragments and sediments.
These materials experience significant abrasion and erosion during transport.
The constant movement and friction cause the edges and corners of rocks to wear down, resulting in rounded shapes.
Sorting: Esker sediments are often well-sorted, meaning particles of similar sizes are grouped together. This sorting is typical of water-transported sediments.
Composition: Eskers contain a mix of particle sizes, from fine sands to larger gravels and boulders1.
Comparison to Other Glacial Deposits
The rounded nature of esker sediments contrasts with some other types of glacial deposits:
Till: Glacial till, deposited directly by ice, often contains more angular rocks because they haven't undergone the same degree of water transport and abrasion4.
Moraines: While moraines can contain some rounded rocks, they generally have a higher proportion of angular fragments compared to eskers.
Significance
The roundness of rocks in eskers is an important indicator of their formation process. It reflects the role of flowing water in shaping and depositing these sediments, distinguishing eskers from other glacial landforms formed by different mechanisms1,4.
1 https://www.antarcticglaciers.org/glacial-geology
2 https://geologyistheway.com/sedimentary/roundness/
3 https://en.wikipedia.org/wiki/Conglomerate_(geology)
4 https://www.britannica.com/science/glacial-landform/Glacial-deposition

GLACIAL TILL FROM IMPACTS?

Glacial till and eskers are often found in proximity to each other, but they are distinct glacial deposits formed through different processes. Here's an explanation of their relationship:
Glacial Till and Eskers
Glacial Till:
Glacial till is a direct deposit of glacial ice, consisting of unsorted sediments ranging from clay to boulders.
It is typically deposited beneath or at the margins of glaciers as they advance or retreat.
Till is characterized by its lack of sorting and stratification.
Eskers:
Eskers are long, winding ridges of stratified sand and gravel deposited by meltwater streams flowing within or beneath glaciers13.
They are formed by the accumulation of sediments in subglacial tunnels or channels.
Unlike till, esker sediments are sorted and stratified due to water transport.
Relationship and Proximity
Spatial Association: Eskers are often found in areas where glacial till is present, as both are products of glacial activity.
Sediment Source: The sediments that form eskers may partly originate from the erosion and reworking of glacial till by meltwater streams.
Depositional Environment: While till is deposited directly by ice, eskers represent the paths of meltwater streams that flowed under or within the glacier.
Landscape Context: In formerly glaciated areas, you might find eskers rising above a landscape covered in glacial till.
Composition Differences
Till: Typically consists of a mixture of unsorted sediments, from fine clay to large boulders.
Eskers: Composed primarily of sorted sands and gravels, with occasional boulders3.
Formation Timing
Glacial till can be deposited throughout the glacial period.
Eskers often form during the later stages of glaciation, particularly as glaciers stagnate or retreat3.
While glacial till and eskers are distinct features, their presence in the same area provides valuable information about past glacial environments and processes. The coexistence of these features helps geologists reconstruct the complex history of glacial landscapes.
1 https://www.britannica.com/science/esker
2 https://www.reddit.com/r/geology/comments
3 https://en.wikipedia.org/wiki/Esker

Glacial Till Thickness
In north-east Scotland, thicknesses of 10 m or more are common.
Individual till units up to 15 m thick have been observed in some sequences.
Average Thickness:
The average thickness of glacial till varies. Some examples include:
In central Buchan (Scotland), tills are generally less than 5 m thick.
In some areas, tills become patchy and rarely exceed 2 m in thickness.

Glacial till thicknesses in Canada vary considerably across different regions:
Greater Toronto Area (GTA)
In the Greater Toronto Area, glacial till deposits show significant variability:
The thickness of glacial till deposits can range from a few meters to over 30 meters in some areas.

Rocks in till are called tillites. In a 2018 article at https://creation.com/some-tillites-may-be-impact-debris Michael Oard said some tillites were formed from landslides during the Great Flood and some tillites "may have formed from meteorite or comet impacts. This idea had been put forward by some researchers in the 1990s,11,12 but the idea was strongly challenged by others.13-15"

An esker ridge trending from right to left (across the centre of this image) in front of the retreating glacier of Renardbreen, at Bellsund, west Spitsbergen. The esker is about 4 m high. {I think there’s Till/Tillite between eskers.}

ICE SHEET IMPACT THEORY

Impacts seem to have spread rock, sand & soil ejecta onto the Canadian Ice Sheet. Cracks formed in the ice where the esker lines are shown on the esker map. Melting ice water flowed in these cracks, carrying along some of the till from the surface, which rounded the rocks that formed into eskers. The angular till rocks left on the surface landed on the ground as the ice sheet melted, leaving them angular. I don't know why the rocks in moraines would be mostly angular, unless with the ice pushing the rocks downhill against the ground, the rocks were not carried in streams like the esker rocks were. The Greenland ice sheet is said to have rock fragments within 50 feet of the bottom, but wouldn't impacts have also spread till over the surface there? The till would tend to sink down through the ice, but maybe it's too thin to detect in the 3 locations where ice cores were taken. The following says eskers are still forming today, but in much smaller amounts.

MAINSTREAM INFO ON ESKERS

Modern Esker Formation
Active Ice Sheets
Eskers are currently forming beneath the ice sheets in Greenland and Antarctica5. These modern ice sheets provide environments similar to those that created the extensive esker networks found in formerly glaciated regions.
Retreating Glaciers
Some of the best examples of modern esker formation can be observed at retreating glaciers:
Breiðamerkurjökull, Iceland: Researchers have documented the annual evolution and internal structure of an englacial esker emerging from this glacier4. This study provides valuable insights into contemporary esker formation processes.
Svalbard: Eskers have been observed forming at glaciers in this Arctic archipelago, including at Høybyebreen1.
Characteristics of Modern Esker Formation
Formation Environment
Modern eskers can form in various glacial settings:
Subglacial: Within tunnels beneath the ice
Englacial: Inside the glacier ice, often exploiting crevasse networks
Ice-marginal: At the edge of glaciers, sometimes entering glacial lakes
Timescales
The formation of eskers can occur relatively quickly in geological terms:
Englacial eskers may evolve significantly over the course of a single year4.
Longer esker systems likely form "time-transgressively," growing at their headward ends as glaciers retreat1.
Preservation Potential
It's important to note that not all forming eskers will be preserved in the long-term geological record:
Englacial eskers, for example, may have low preservation potential due to post-depositional modification as they melt out of the ice4.
Eskers forming on soft, deformable beds are less likely to be preserved than those on harder substrates2.
Implications
Studying modern esker formation provides valuable insights into glacial processes and helps interpret the extensive esker networks left behind by past ice sheets. However, the smaller scale of most modern glaciers means that the eskers forming today are generally not as extensive as the large systems formed during continental glaciations1.
1 https://onlinelibrary.wiley.com/doi/full/10.1002/esp.5664
2 https://www.worldatlas.com/articles/mountain-and-glacial-landforms-what-is-an-esker.html
3 https://en.wikipedia.org/wiki/Esker
4 https://www.britannica.com/science/esker
5 https://www.gov.nt.ca/sites/ecc/files/wkss_esker_habitat_characteristics_2001.pdf

Esker tunnels form beneath glaciers through a complex interplay of glacial hydrology, ice dynamics, and sediment transport. Here's an overview of how these subglacial tunnels develop:
Tunnel Formation Process
Meltwater Accumulation
Meltwater from the surface of the glacier can reach the base through:
Moulins (vertical shafts in the ice)
Crevasses
General percolation through the ice
This water, combined with meltwater produced at the base of the glacier, accumulates under high pressure beneath the ice1.
Channel Initiation
As water accumulates, it begins to flow in the direction of least resistance:
Initially, water may flow through a network of interconnected cavities
Over time, some flow paths become preferential, concentrating water flow3
Tunnel Expansion
The concentrated flow of water in these preferential paths leads to tunnel formation:
Frictional heat from water flow melts the ice walls, enlarging the tunnel
The tunnel expands upward into the ice due to the inability to erode the bedrock below1
Factors Influencing Tunnel Development
Ice Pressure
The pressure of the overlying ice tends to close the tunnel
This closure is counteracted by the melting of the tunnel walls
Water Pressure
High water pressure can force water to flow uphill against gravity
Pressure fluctuations affect the tunnel's size and shape1
Sediment Supply
Debris from the surrounding glacial ice is released into the water as the tunnel walls melt. This sediment is crucial for esker formation, as it's deposited within the tunnel3,4
Bed Topography
The underlying terrain influences the path of the tunnel, though not entirely determining it. Tunnels can cross topographic divides due to pressure gradients in the ice4.
Tunnel Characteristics
Shape: Tunnels often develop an arched or semi-circular cross-section
Size: Can vary greatly, from small conduits to large tunnels several meters in diameter
Stability: Tunnels may open and close seasonally or in response to changes in water supply
Esker Formation
As these subglacial tunnels carry sediment-laden water:
Coarser sediments (gravel, sand) are deposited within the tunnel. Finer sediments may be carried to the glacier margin. Over time, this deposition builds up the ridge-like structure of the esker3.
The process of esker formation is often "time-transgressive," meaning the esker grows at its headward end as the glacier retreats, potentially over thousands of years5.
Understanding the formation of these subglacial tunnels is crucial for interpreting the extensive esker networks left behind by past ice sheets and for studying modern glacial hydrology.
1 https://en.wikipedia.org/wiki/Esker
2 https://onlinelibrary.wiley.com/doi/full/10.1002/esp.5664
3 https://www.gov.nt.ca/sites/ecc/files/wkss_esker_habitat_characteristics_2001.pdf
4 https://serc.carleton.edu/vignettes/collection/36395.html
5 https://uphere.ca/articles/how-are-eskers-formed

It’s not clear how esker material gets squeezed into the subglacial tunnels, so I think the theory that impact ejecta spread the Till/Tillites onto the ice sheets where streams of water moved some of the tillites into the esker tunnels could be an excellent explanation as the source of the rocks, sand and clay in the eskers. There could have been tillites on the ground before the ice sheets formed, but that seems less likely to be the main source of the esker material.