3.b. Submergent coastal landscapes form as sea level rises

When did climate change occur in a previous time period? (sea level rise)

• Würm glacial period - 25,000 years ago

What happened to the temperature during the Würm glacial period?

• Global mean annual temperature were ~9° lower than today

What happened to the resultant sea level during the Würm glacial period?

• Sea level was ~90m lower than today’s position

What happened during the Flandrian Transgression?

• A period of significant sea level rise following the last ice age

How does a warming climate result in sea level rise?

• Higher rates of melting of land ice (sheets, caps and glaciers)

What is the relationship between temperature and sea level?

• A 1°c rise in mean global temperatures = a ~2m sea level rise

When do submergent landforms appear?

• When the sea level has risen (or the land level has fallen)

What are the different types of submergent landforms?

• Rias

• Fjords

• Shingle beaches

What are rias?

• Submerged (winding) river valleys - gently sloping

• Middle/upper is exposed

• Deeper towards the centre

Where are rias located?

• Unglaciated valleys (formed during the post-glacial sea level rise of the Flandrian Transgression)

How were rias formed?

• Flandrian Transgression - submergence of low lying river valleys

• Funnel shaped, branching inlets decreasing in depth and width inland were formed

What are rias typically underlain by?

• Alluvial deposits in buried channels that were eroded by the rivers (Pleistocene glacial periods)

How might rias be modified in the future?

• If sea level rises, tidal action and wave energy reshapes the inlet

• The intertidal zone may shrink

• Barrier islands may form

What are fjords?

• Submerged (deep) glacial valleys with steep valley sides

Where are fjords located?

• In U-shaped valleys

How were fjords formed?

• Glaciers erode (stronger inland, weaker at the mouth) the bedrock by abrasion

• This leaves a shallow rocky ridge or a sill, restricting water exchange with the open sea

How might fjords be modified in the future?

• If sea level rises - marine processes, increasing depth of submerged areas, isostatic rebound

• If sea level falls (valley) - sub-aerial weathering and (submarine) landslides

What do fjords have that rias don’t?

• Glacial rock basin with a shallower section (threshold)

• Straighter platforms (glacier truncated interlocking spurs)

How might future sea levels affect both rias and fjords?

• Sea levels are predicted to rise by 0.6m in the next 100 years

• Stormier conditions, larger waves - frequent rates of marine erosion

What is a shingle beach?

• Large pebble beaches which are formed as the volume of land-based ice grows

Where are shingle beaches located?

• High energy areas (or, at the base of former cliff lines - may form tombolos/bars)

How are shingle beaches formed?

• Sediments were deposited on the continental shelf (above sea level)

• Rising sea levels over the past 20,000 years have deposited it on coasts

How might shingle beaches be modified in the future?

• If sea level rises, sediment deposits more frequently (longshore drift) leading the beach landwards over its own lagoon