How are glacial erratics transported to their resting places?
A glacial erratic is a rock transported and deposited by a glacier, often unlike the local bedrock. A solitary boulder in a field or on exposed rock can be a striking sign of former ice transport.
The journey of a detached rock
Fragments may be plucked from the glacier bed or fall from neighbouring slopes onto the ice. Transported within, above or beneath it, a block is released by melting. Its edges may be worn during transport, but not all erratics become rounded. Travel distance is investigated by comparison with possible source rocks; large size alone does not prove long-distance movement.
Why the source matters
Mineral composition and texture are compared with possible source areas. Distribution can help reconstruct ice routes, although repeated glaciations complicate interpretation. Not every apparently foreign rock is an erratic: landslides, powerful water flows and human activity can also move blocks. Moraines, glacial scratches and geological maps must therefore be considered together. Preserving a block's location protects scientific evidence of landscape history as well as its visual interest.