ENVIRONMENTAL HISTORY

PHYSICAL ENVIRONMENTS

The region's physical setting has undergone major changes in the last 15,000 years. In the cold and dry early stage of the region's history, 15,000-13,000 years ago, glacial processes dominated the landscape. Ice accumulated at high and medium elevations and flowed down valleys onto the plateau and then out deep valleys like the Okanagan Valley to the edge of the Cordilleran ice sheet (Ryder and Clague 1989). Glacial refugia likely existed at high elevations, especially at sites such as the Cathedral Lakes Park of the southern interior, near the margins of the ice sheet. But at this point their character and extent is not known.

As glacial ice retreated during warming 13000 - 10000 years ago, ice-eroded debris was left behind as a blanket of till or reworked by meltwater into fluvial and lake deposits. Large glacial lakes formed in major basins, such as the Thompson, Fraser and Okanagan systems, as the ice sheet broke up and melted away. The landforms left behind by glacial activity established much of the substrate upon which modern-day ecosystems developed.

Sudden and major warming of several degrees Celsius at the beginning of the Holocene Epoch 10,000 years ago, led to the development of arid land processes characteristic of hot dry climates, especially in the south. The generally wet landscape of the late glacial episode dried up as water evaporated and rivers and streams incised lowering lake levels. Dry-land processes such as wind erosion and precipitation of salts predominated.

About 7000 years ago moistening and possibly cooling climate led to increasing water levels in lakes (Mathewes and King 1989) and decreased eolian activity. From 4000-5000 years ago cooling and moistening climate stimulated glacial re-advances at high elevations, major growth of lakes and ponds and development and expansion of wetlands (Hebda 1995). At one site in the southern Okanagan valley, this climatic a change may have led to increased erosion and a major stage in aggradation (in-filling) of the valley bottom (Ruck et al.1997). Arctic and alpine geomorphic processes such as solifluction and cryoturbation likely returned at high elevations.