key idea 3a: how do coastal landforms evolve over time as climate changes?

emergent landscapes are shaped significantly by falling sea levels, often linked to cooling climates. these landscapes provide valuable insight into past and present geomorphic processes.

what happened in the quaternary period?

• experience glaciations/ice ages → substantial cooling of global climate

• large water volumes were trapped in ice sheets/glaciers → drop in sea level. 20,000 years ago sea level was approx. 120m lower than present levels

what happens when sea levels fall?

• submerged land areas are exposed → emergent landforms

• primary geomorphic processes: erosion, weathering, deposition.

• form raised beaches, marine terraces and abandoned cliffs

how do raised beaches form?

• former shorelines are elevated above sea levels due to sea level fall + isostatic rebound

• consist of wave-cut platforms and beach deposits that are located inland + higher elevation

how are marine terraces formed?

• step-like landforms created by sea-level change + tectonic uplift

• sea level fall, waves erode bedrock → create flat, bench-like platform. sea level stabilise temporarily, terrace is formed.

• fall in sea levels/tectonic uplift → series of terraces at different elevations, each representing a former sea level.

how are abandoned cliffs formed?

• steep slopes/escarpments that mark former position of the coastline

• actively eroded by wave action when sea levels were higher. sea level fell → wave action shifted eastward → leaves cliffs abandoned inland

present climate change

• e.g global warming → sea level rise → thermal expansion of seawater + melting of ice caps + glaciers

• lead to re-submergence of emergent landforms → alters structure via wave action, erosion

future climate and sea level changes

• continue sea level rise → submerge raised beaches + marine terraces → back to active coastal system

• abandoned cliffs → renewed erosion is wave action reaches base → slope instability + increased landslides

• ongoing tectonic acticity, isostatic adjustments + sea level change → modify emergent landscapes