Drift (geology)
Drift, in geology, refers to all material of glacial origin found anywhere on land or sea. This includes sediment deposited directly by glaciers (till) as well as sediment deposited by glacial meltwater streams (outwash), glacial lakes (lacustrine deposits), and the sea (marine deposits). The term "drift" is often used to describe unconsolidated surface deposits, regardless of their exact mode of deposition, but always implying a glacial origin.
The term originated from the early belief that these materials were "drifted" into place during a great flood (a diluvial theory). While the understanding of the processes involved has evolved considerably, the term "drift" has persisted in geological nomenclature.
Glacial drift encompasses a wide range of particle sizes, from enormous boulders to fine silt and clay. The composition of the drift reflects the geology of the areas over which the glacier flowed, and thus can provide clues to the source regions of the ice. The thickness of drift deposits can vary significantly, from a thin veneer to hundreds of meters in depth, depending on the local topography and glacial history.
Key types of glacial drift include:
- Till: Unsorted and unstratified sediment deposited directly by ice. Typically contains a heterogeneous mixture of particle sizes ranging from clay to boulders.
- Outwash: Sorted and stratified sediment deposited by glacial meltwater streams. Often consists of sand and gravel.
- Lacustrine Deposits: Fine-grained sediments (silt and clay) deposited in glacial lakes.
- Marine Deposits: Sediments deposited in marine environments influenced by glacial activity, such as ice-rafted debris (IRD) and fine-grained sediments carried by meltwater plumes.
The study of glacial drift is crucial for understanding past glacial activity, reconstructing paleoclimates, and assessing potential hazards related to unstable slopes and ground conditions. Understanding the distribution and properties of drift is also essential for resource exploration, agriculture, and civil engineering.