as it surges forward, it moves large sheets of frozen sediment at the base along with the glacier. Glacially induced spalling occurs when ice lens formation with the rocks below the glacier spall off layers of rock, providing smaller debris which is ground into the glacial basal material to become till. Evidence supports another option for creation of erratics as well, rock avalanches onto the upper surface of the glacier (supraglacial). Rock avalanche–supraglacial transport occurs when the glacier undercuts a rock face, which fails by avalanche onto the upper surface of the glacier. The characteristics of rock avalanche–supraglacial transport includes: Monolithologic composition – a cluster of boulders of similar composition are frequently found in close proximity. Commingling of the multiple lithologies normally present throughout the glaciated basin, has not occurred. Angularity – the supraglacially transported rocks tend to be rough and irregular, with no sign of subglacial abrasion. The sides of boulders are roughly planar, suggesting that some surfaces may be original fracture planes. Great size – the size distribution of the boulders tends to be skewed toward larger boulders than those produced subglacially. Surficial positioning of the boulders – the boulders are positioned on the surface of glacial deposits, as opposed to partially or totally buried. Restricted areal extents – the boulder fields tend to have limited areal extent; the boulders cluster together, consistent with the boulders landing on the surface of the glacier and subsequently deposited on top of the glacial drift. Orientations – the boulders may be close enough that original fracture planes can be matched. Locations of the boulder trains – the boulders appear in rows, trains or clusters along the lateral moraines as opposed to being located on the terminal moraine or in the general glacial field. Glacier-borne erratic Erratics provide an important tool in characterizing the directions of glacier flows, which are routinely reconstructed used on a combination of moraines, eskers, drumlins, meltwater channels, and similar data. Erratic distributions and glacial till properties allow for identification of the source rock from which they derive, which confirms the flow direction, particularly when the erratic source outcrop is unique to a limited locality. Erratic materials may be transported by multiple glacier flows prior to their deposition, which can complicate the reconstruction of the glacial flow. Ice-rafted erratic Glacial ice entrains debris of varying sizes from small particles to extremely large masses of rock. This debris is