Overview:
Spanning over 55 hectares, the Champion Lakes Regatta Centre is the home of rowing in Perth. It regularly hosts competitions for rowing, canoeing, dragon boating, triathlon and more. Moreover, the parkland surroundings, barbeque facilities and dedicated public swimming areas make the Champion Lake Regatta Centre perfect for all community members.
What is basalt:
Basalt s an extrusive igneous rock, meaning it forms when molten lava reaches the surface and cools rapidly. This quick cooling process prevents large crystals from growing, giving basalt its characteristic fine-grained (aphanitic) texture. it's appearance is typically dark gray to jet black when fresh, though it can weather to rusty red or brown due to high iron content
How is basalt formed (In steps):
1. Melting of the Mantle:
It all begins in the Earth's mantle (the layer below the crust). When rocks in the upper mantle melt—usually due to a drop in pressure or an increase in temperature—they create a runny, iron-rich liquid called mafic magma.
2. The Journey Upward:
Because this magma is less dense than the solid rock surrounding it, it rises toward the surface. It travels through cracks and fissures in the Earth's crust.
3. Eruption (Extrusion):
Once the magma reaches the surface, it is called lava. Basalt forms from extrusive eruptions, meaning the lava flows out onto the land or the ocean floor rather than staying trapped underground.
- On Land: It can erupt from volcanoes (like in Hawaii) or through long cracks in the ground called fissures, creating massive "flood basalts."
- Underwater: At mid-ocean ridges, lava erupts and cools instantly against the cold seawater, often forming rounded shapes called pillow basalts.
4. Rapid Cooling:
This is the most important part: basalt cools very quickly. Because it hits the relatively cool air or water, the minerals don't have enough time to grow into large, visible crystals. This results in the fine-grained, stony texture.
Weathering and Erosion on this rock:
1. Chemical weathering (the "rust" factor):
- Oxidation: just like an old car, the iron in basalt reacts with oxygen and water to form iron oxide (rust). this is why a basalt rock might be pitch black on the inside but have a rusty red or orange "skin" on the outside.
- Carbonation: rainwater is slightly acidic because it absorbs from the atmosphere. this weak acid slowly dissolves the calcium and magnesium in the basalt, turning the hard rock into soft clay minerals.
2. Physical weathering (the "crack" factor):
- Mechanical fracturing: as lava cools, it naturally develops cracks (joints). water seeps into these cracks, freezes, and expands (frost wedging), eventually splitting the rock into jagged chunks like the one in your photo.
- Thermal expansion: in deserts, basalt gets very hot during the day and cold at night. this constant "breathing" causes the outer layers to peel off like an onion, a process called exfoliation.
3. Erosion and Transport:
- River transport: pieces of basalt are carried downstream. because they are so hard, they act like sandpaper, grinding down the riverbed while getting rounded into smooth, black river stones.
- Black sand beaches: when basalt reaches the ocean, the powerful surf mashes it into tiny grains. this is exactly how the famous black sand beaches in hawaii and iceland are created.
How to obtain the cache find:
In order to log this cache find you will have to send me a private message either by email or GC Messenger with the answers to the cache.
- What type of rock you can find here and how do you think it is formed?
- What weathering and erosion can you see at the the rock?
- Observe the rock is it smooth or rougth in texture and why do you think it is like this?
- Take a photo of your self or a personal object that clearly shows your team name. showing the rock