The Portsea Bridge lookout is only a short walk from the car park provides stunning views of the Bridge, the beach and the rock platforms below. Views east towards Portsea and north-west towards Point Nepean National Park.
Beach access is via a steep ramp. A large rock platform provides for great snorkeling and exploring the rock pools at low tide
Large area of native coastal vegetation along the cliff tops provide habitat for large variety of birds and some of the park’s rarest mammals such as Long-nosed bandicoots and White-footed dunnarts.
Sometime before 6000 BC, (after the end of the most recent Ice Age about 8000 BC), the Yarra River was probably joined with other tributaries such as rivers now called the Patterson, Kororoit, Werribee and Little. They drained directly into Bass Strait through what is now called the Rip. Between 8000 BC and 6000 BC, the basin flooded forming Port Phillip Bay and moving the "mouth" of the Yarra over 50 km inland.
A dry period combined with sand bar formation may have dried the bay out as recently as between 800 BC and 1000 AD extending the yarra to bass strait during this period.
Most limestone form in shallow, calm, warm marine waters. That type of environment is where organisms capable of forming calcium carbonate shells and skeletons can easily extract the needed ingredients from ocean water. When these animals die their shell and skeletal debris accumulate as a sediment that might be lithified into limestone. Limestone is what makes up the Portsea Bridge.
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crustal forms of calcium carbonate (CaCO3). Most limestone is composed of skeletal fragments of marine organisms such as coral or forminifera.
Limestone makes up about 10% of the total volume of all sedimentary rocks. The solubility of limestone in water and weak acid solutions leads to karast landscapes, in which water erodes the limestone over thousands to millions of years.
Limestone
Limestone is partially soluble, especially in acid, and therefore forms many erosional land forms. These include limestone pavements, pot holes, cenotes, caves and gorges. Such erosion landscapes are known as karstss. Limestone is less resistant than most igneous rocks, but more resistant than most other sedimentary rocks. It is therefore usually associated with hills and downland, and occurs in regions with other sedimentary rocks, typically clay.
Karst topography and caves develop in limestone rocks due to their solubility in dilute acidic groundwater. The solubility of limestone in water and weak acid solutions leads to karst landscapes. Regions overlying limestone bedrock tend to have fewer visible above-ground sources (ponds and streams), as surface water easily drains downward through joints in the limestone. While draining, water and organic acid from the soil slowly (over thousands or millions of years) enlarges these cracks, dissolving the calcium carbonate and carrying it away in solution. Most cave systems are through limestone bedrock. Cooling groundwater or mixing of different ground waters will also create conditions suitable for cave formation. Coastal limestone are often eroded by organisms which bore into the rock by various means.
Questions to log this Earth Cache
Q1According to the sign this famous landmark had been formed through the weathering action of how many years and from what three things?
Q2 Estimate the height of the Bridge?
Q3 What colours do you see in the Limestone and describe the texture of the rock?
Please do not climb on the bridge, you will not need to for obtaining the answers for this Earth Cache. You will however need to go down to the listed coordinates which are on the sand.
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