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3.2.1 Glacial Ice-Laid Deposition

Below the surface, ice-laid deposits are unsorted and unstratified. This material is called till, and can vary from 99% clay to 99% boulders depending on the nature of the transported material at deposition. Till generally can be divided into two categories: Lodgement and ablation. The Lodgement till is deposited directly on the usually at the base of the glacier. The stones tend to be aligned with the long axes parallel to the direction of ice flow. Lodgement till is compacted and may acquire a fissile structure; crushing and abrasion of particles are considerable. Ablation till is deposited on or near the terminal area of a shrinking glacier. The material is let down or dropped as the ice melts so the the till is often loose, uncompacted, and nonfissile. Although the particles may retain an orientation parallel to ice movement, the smaller particles are often re-oriented by settling as the ice melts. Because the ablation till consists only of the load at the time of melting, this till is usually much thinner than the lodgement till.

The surface ice-laid features include ground moraine, terminal moraine, recessional moraine, lateral moraine, drumlins, boulder trains, and erratics. The moraine deposits and drumlins may be exposed on the surface and extend to a considerable depth. The deposits may also be covered by other deposits which can bury the till.


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