Look up the "channeled scablands" of eastern washington. we see river landforms on massive scales. for example, ripple marks which are normally a few centimeters high are several meters high. how could a river create river formations on a such a large scale? question 21 options: -a large river carved these features over thousands of years of high flow. -a north-flowing river was blocked by ice forming an ice dam. the ice dam broke flooding the landscape.- -a large glacier was halted by a mountain as it was moving forward. water built up along the base of the glacier causing high water pressure. the glacier rose slightly due to underlying water pressure. water rushed out catastrophically flooding the landscape. a major ice dam broke and glacial lake missoula flooded the landscape in short period of time.