The resulting wave of water removed overburden and exposed bedrock. The overburden is removed to allow access to the ore. Both overburden and lignite production has been outsourced. At times, excavated areas collapsed from overburden. This can occur at times of rapid overburden erosion. Fracture gradients normally increase with depth due to increasing overburden pressure. The excavating head itself is in diameter and has 18 buckets each holding of overburden. BWEs are used for continuous overburden removal in surface mining applications. The ratio of overburden to coal is 6.2&colon;1. Unloading is the release of pressure due to the removal of an overburden. High capacity excavators are used for handling a large volume of overburden, after forward preparation. The barrel was dug into the roadside with a substantial overburden and camouflaged. In some areas, ice has scoured rock surfaces bare, entirely stripping off the overburden. About 10% of the Athabasca oil sands are covered by less than of overburden. This was dug into the roadside with a substantial overburden and camouflaged.