Isostasy (Leaving Cert Geography): Revision Notes

Cyclical Landscape Development

Cyclical Landscape Development

Landscape Development is cyclical. It happens in three main stages:

Early Stage:

• The landscape is flat to begin with
• It quickly becomes high and rugged through the tectonic process of folding
• Mountains are created

Middle Stage:

• Vertical erosion begins to shape the landscape as streams and rivers carve out valleys
• Floodplains are created through lateral erosion as the valleys become flatter
• The angle of slope decreases constantly throughout this cycle as the landscape becomes flatter towards the sea

Late Stage:

• Lateral Erosion, Mass Movement and Deposition combine to form peneplains (areas of flat land).
• No more erosion can take place at this stage
• The base level has been reached

The South Ireland Peneplain

• Covers hundreds of square kilometres in Co. Waterford and Co. Cork
• Best example can be seen in the Knockmealdown Mountains with the height of land varying between 180m and 240m above todays sea level
• Formed on the sandstone uplifted during the Armorican folding and consists of a reasonably flat landscape with some individual hills
• The sandstone was worn down to a peneplain by an ancient river system
• The peneplain was later submerged beneath the sea where layers of limestone and chalk were formed over it
• Later uplift brought the land back above sea level again