Subglacial bedrock brecciation is the fracturing or shifting of bedrock by thermal or mechanical action beneath a cold glacier. Thermal action results when migrating groundwater freezes in bedrock upon approaching the glacier base. Mechanical action results when a deforming cold glacier applies normal stress or basal shear stress exceeding the strength of bedrock substrate. Subglacial bedrock brecciation can occur on scales ranging from millimeters to meters.
An example of subglacial bedrock brecciation resulting from thermal action is shown in the above photo. Although it is a subglacial process, this type of bedrock brecciation can closely resemble subaerial bedrock frost heave.
A subglacial bedrock brecciation process working at the centimeter scale has delaminated foliated bedrock overlying a small pseudo-fissure. The pseudo-fissure was not formed by the lateral displacement of adjacent sections of intact bedrock. Rather, the pseudo-fissure was formed by the horizontal and vertical displacement of small bedrock fragments by pressurized ice. The above-illustrated feature is described in more detail in the section on pseudo-fissures.
AvalonSubglacial