450 m terrace

 

 

 

 

 

 

 

 

The Eag Mhór spillway

 

 

 

 

 

 

 

 

 

580 m and 600 m terraces

 

 

Faesheallach Burn

Bremner (1932) identified the essentials of the geomorphology of the embayment SE of Carn na h-Ailg drained by the Faesheallach Burn. The embayment contains a striking suite of ice-marginal landforms which form part of a wider group that records the advance and retreat of a lobe of Strathspey ice against the flanks of the northern Cairngorms.

The spillways across the col south of Carn na h-Ailg at ~570 m OD demonstrate that the ice at one time filled the embayment. Terraces at ~600 and ~580 m OD indicate positions of the ice margin and ponding of small lakes which probably relate to lateral meltwater channels and moraines on the flanks of Carn Mheadhair. A large kame terrace covering ~0.45 km2 has a top at 450 m and a steep ice-contact slope to the NW, with probable lateral moraines on its rim. Meltwater flowed NE through the gorge of the Eag Mhór.

Sediments exposed in stream sections provide support for pattern of ice advance and retreat proposed by Bremner. The upper terraces show a basal till derived from erosion of the local grey psammite. Ice movement into the embayment is indicated by overturning to the SE of steeply dipping psammite beds. The till is overlain by 10 m or more of stacked tills, deformed sand units and cobble and boulder gravels. The sequence suggests that after an initial advance the ice margin oscillated at this location, with ice pushing forward to over-ride, erode and deform sands deposited in marginal ponds. The 450 m terrace has a simpler stratigraphy, with ~10 m of undeformed, horizontally bedded sand overlain by coarse gravel that may include till layers. The ice-marginal lake sands here were deposited at a relatively static ice margin, prior to possible readvance of ice across parts of the former lake bed.