Isostasy Cycle of movement of Earth’s crust: Chapter 14: Isostasy The upper section of Earth’s crust eroded Continental crust rises upwards Glacial ice pushes continental crust downwards Glacial ice melts, landmasses rise upwards

When land is uplifted, a change in a river’s base level occurs Chapter 14: Isostasy When land is uplifted, a change in a river’s base level occurs Ability to erode is reborn Rejuvenation occurs

Eustatic movement Changes in the amount of water in oceans Chapter 14: Isostasy Eustatic movement Changes in the amount of water in oceans Linked to global climatic change Earth’s climate cools water stored in glaciers Reduction in sea level Ice age ends Rise in sea level

Exogenetic forces Processes which occur at or near the Earth’s surface Chapter 14: Isostasy Exogenetic forces Processes which occur at or near the Earth’s surface E.g. erosion as a result of wind, water, ice and activities of animals and humans

Endogenetic forces Processes operating below the Earth’s crust Chapter 14: Isostasy Endogenetic forces Processes operating below the Earth’s crust Form surface features such as folds, faults and volcanoes

Isostatic equilibrium Chapter 14: Isostasy Isostatic equilibrium Balances of forces due to varying weights of landmasses in close proximity to each other

Chapter 14: Isostasy Base level Generally equal to sea level

Features of adjustment to base level Chapter 14: Isostasy Features of adjustment to base level 1. Knickpoints Sudden change in the slope of the long profile of a river Evidence of rejuvenation ‘Rebirth’ of erosive power that is only found usually in the youthful stage of a river Usually marked by waterfalls or rapids e.g. Kathleen’s Falls, River Erne, Ballyshannon, Donegal

Features of adjustment to base level Chapter 14: Isostasy Features of adjustment to base level 2. Incised meanders Incised means ‘cut deeply’ Caused by vertical erosion River erodes down into its floodplain Creates incised meanders e.g. River Nore at St Mullins in Co. Carlow

Features of adjustment to base level Chapter 14: Isostasy Features of adjustment to base level 3. Terraces Rejuvenated river Vertical erosion in old stage River has a wide floodplain Waterfalls form River erodes in the old stage New floodplain forms by lateral erosion Old floodplain appears like a step above the new floodplain Steps also known as terraces On both sides of a river, called paired terraces e.g. along the River Barrow, Co. Kilkenny

Features of adjustment to base level Chapter 14: Isostasy Features of adjustment to base level 4. Raised beaches Common in glaciated regions Glaciation ends, level of the land surface readjusts Former beach left located above the coastline/shoreline of current sea level e.g. Donegal Bay

Development of a landscape Chapter 14: Isostasy Development of a landscape Three stages: Early Middle Late

Development of a landscape Chapter 14: Isostasy Development of a landscape 1. Early stage Topography flat Narrow streams and rivers

Development of a landscape Chapter 14: Isostasy Development of a landscape 2. Middle stage Vertical erosion Valleys carved out

Development of a landscape Chapter 14: Isostasy Development of a landscape 3. Late stage Lateral erosion Floodplains Peneplain – rare occurrence

Peneplains Low relief plain close to a river Flat surface Chapter 14: Isostasy Peneplains Low relief plain close to a river Flat surface Lies at an elevation close to sea level Result of long-term erosion e.g Munster Peneplain