CORE UNIT: PATTERNS AND PROCESSES IN THE PHYSICAL ENVIRONMENT View from above A B
1. Landforms associated with drowned/submerged coastlines
(a) Rias 0 Profile of sea floor
A ria is a drowned river valley, e.g. Kenmare Bay in County Kerry and Shannon Estuary in County Limerick/Clare. Rias form where sea levels rise relative to the land
20 30 AB Distance Fig. 50 Exam Diagram: A ria
either as a result of eustatic sea level change (where the global sea levels rise) or isostatic sea level change (where the land sinks). When this happens coastal valleys which were previously at sea level become submerged/ flooded. The result is often a very large estuary at the mouth of a relatively small river. Rias are common across south-western Ireland and Europe, e.g. the mouth of the River Severn in the UK and the north Brittany coastline of France.
(b) Fiords
Fiords are drowned glaciated valleys, e.g. Killary Harbour in County Mayo. They are formed when a glacier cuts a U-shaped valley by plucking and abrasion into the surrounding bedrock. In countries such as Norway and Greenland the glaciers flow into the sea so their glaciated valleys open into the sea. When ice sheets melt, the meltwater flows into the sea and causes the sea level to rise which then floods the U- shaped valley. Fiords generally have a sill or rise at their mouth caused by the previous glacier's
deposition of a terminal moraine. In many cases these cause extreme tidal currents and rapids at the entrance to the fiord.
Rias and fiords have several differences: • Rias get shallower towards the land.
• Fiords get deeper towards the land.
• Rias are V-shaped and wider at their mouths with gently sloping sides.
• Fiords are long and narrow with steeply- sloping sides.