Blind valleys

Gaping Gill blind valley

In Britain, valleys in areas of massive limestones are usually dry due to the permeable nature of the rock. However, in some cases rivers flow over rocks such as shales or sandstones before they flow onto the limestone.

The rivers may be able to flow over the limestones for a short distance (perhaps on till), but eventually they disappear underground, leaving a series of features called 'blind valleys'.

In the past, blind valleys have developed at Ingleborough, Yorkshire. Here, rivers originating on the upland areas of sandstones, shales and grits, flow onto the Carboniferous limestone for a short distance before disappearing underground, leaving a series of blind valleys.

How do blind valleys form?

  1. A river flows over the limestone until the joints have opened up sufficiently and the stream disappears down a swallow hole. The valley downstream is dry and erosion stops here.
  2. Upstream of the swallow hole, river erosion continues. As a result of continued erosion at the swallow hole or sinkhole, a hollow may be formed, perhaps with a small cliff facing uphill. This is a blind valley.
  3. Over time, a new sinkhole or swallow hole develops high in the valley and the older one downstream is abandoned. With erosion at this new site, another blind valley may form.
  4. This may occur several times so that a series of blind valleys, with the youngest one being uphill, is created.
  5. With time, the hole down which the river disappears reaches the point where the non-limestone and limestone meet.