The end of the gouge.
When the ice cap retreated during the last glacial period, a deep lake was formed in a valley above the present gorge, the water being retained behind a threshold of rock,
with overflow water running down the slope now cut by a gorge. As rivers fed by the edge of the ice cap deposited a lot of sediment in the lake, the spill-water eroded the rock threshold and the hyaloclastite in front of it.
The result was a poverful watercourse that cut the gorge se see today. Eventually it dwindled as the lake filled up and the river cut its way lower and lower into the sediment in the valley.
It is still doing this, but the flow rate is now feeble and it has little influence on the deep channel in the hyaloclastite.