EROSION
Erosion is the wearing away of rock along the coastline
Destructive waves are responsible for erosion on the coastline
Where does coastal erosion occur in australia ? The most vulnerable coasts are made up of unconsolidated sediments ,such as beaches dunes and sand cliffs,on opencoasts that experience net longshore drift of sediment and on the shores of coastal lakes and lagoons .
There are four types of erosion
Hydraulic action -this is the sheer power of the waves as they smash against the cliff .Air becomes trapped in the cracks in the rocks and causes the rock to break apart.
Abrasion -this is when pebbles grind along a rock platform much like sandpaper .Over time the rock becomes smooth .
Attrition -this is when the rocks that the sea is carrying knock against each other .They break apart to become smaller and more rounded
Solution -this is when the sea water dissolves certain types of rock such as chalk and limestone .
A short walk from the old Jail ruins will lead you to ground zero where you can observe the erosion occuring here at the Cape Dombey cliffs .
At the end of the cliff is the OBelisk .
THE OBELISK
The Obelisk was erected on Cape Dombey in 1852 and was used to navigate the entrance to Guichen Bay ,as well as to store rocket life saving equipment .The firing of rockets ,carrying baskets to distressed ships to bring passengers ashore,saved many lives .It later assisted passing ships with navigation because its height of 12m(40ft) makes it visible 20km(12miles) out to sea .The Obelisk was painted red and white so it could be seen against the white sand dunes .It is made of small limestone rocks mortared together
The Obelsik is situated along the sandstone cliffs which are gradually being eroded by the Southern Ocean and will result in it falling into the sea.
It is now unsafe to walk up to the Obelisk and workplace health and safety rules make it too expensive to maintain the structure because of risks involved .
Please send your answers to questions below then ok to log as a find .I will contact you if needed .
Q1
What type of erosion has occured at the cliff face and why ?
Q2
Do you think the rocks used to build the Obelisk were locally obtained and why ?
PLEASE OBIDE BY OF ALL WARNING SIGNS AND STAY BEHIND THE BARRIERS .
Information relating to this cache were obtained from
www.ga.gov.au>hazards>coastalerosion
District Council of Robe
www.bbc.com>guidesGSCE-geology coastal erosion