You will need to park your vehicle at pullouts at either end of the bridge and walk onto the bridge. It’s not a busy road so you should have time to visit the earthcache and collect the information you need to answer the questions below.
In scientific terms, the geology of the area is based on the Karmutsen Group, which consist of rocks formed from thick lava flows. Another formation known as the Nanaimo Group is composed of younger rocks which overlie the Karmutsen Group. The Nanaimo Group are composed of conglomerates, sandstones, siltstone and shales. They often form fault lines in contact with the older Karmutsen rocks.
The main rock types commonly found in the Oyster River area is sedimentary rock from the Nanaimo Group, along with some metamorphic, and igneous rock types from the Karmutsen Group.
The three rock types can be seen at this spot and it’s your job to figure out what you are looking at. The descriptions below will help you in that regard and in answering the questions posed below:
Sedimentary rocks are formed by the consolidation of sediments (particles of sand, silt, clay, pebbles, and other fragments). Gradually over a long period of time and combined with environmental factors (weathering, erosion, deposition, transportation), the sediment accumulates in layers and eventually hardens into rock. As sedimentary particles are eroded from other rock types at higher elevations (weathering & erosion), they tend to migrate towards the sea driven by the energy of water and gravity (transportation). Various factors including general landforms, the amount of energy provided by water/gravity, and other elements will influence the type of sedimentary rock that is formed (deposition). Generally, sedimentary rock is fairly soft and may break apart or crumble easily.
Igneous rocks are formed when magma (molten rock deep within the earth) reaches the surface, cools and hardens. When the magma cools slowly below the earth’s surface, the resulting rock will exhibit a coarse grained crystallized appearance. When the molten material erupts to the surface quickly in the form of lava, it will cool quickly, and the resulting rock will exhibit a fine glasslike appearance. Sometimes gas bubbles are trapped in the lava during the cooling process, leaving tiny holes and spaces in the rock.
Metamorphic rocks are rocks that have been altered from their original conditions. These rocks are produced by transformations that take place at pressures and temperatures much higher than are found at the earth’s surface, but below the temperatures that induce melting. The pre-existing rock that is transformed (metamorphosed) may be igneous or sedimentary rock. The rock that results from this process is composed of mineral crystallization and often has a wavy or ribbon-like pattern.
To log this cache you must answer a few questions that can be found by visiting the site. Please email me your answers. Do not post your answers with your log otherwise it will be deleted. The area is best visited when water levels are low.
1) From the bridge, look upstream and to the left of the river you will see a shelf of rock. From the three rock types listed above, what type of rock do you see? What features do you see that made you come to that conclusion? Which Group would you say this rock is from and why?
2) Looking downstream towards the bank at the sharp bend in the river, you will see another type of rock formation. What type of rock do you see and how did you come to that conclusion? Which Group is this from and why?
3). Again, looking downstream and to your right, you will notice a steep rock wall along the river. Compare this to the feature from question 2. What type of rock formation are you looking at, and what differences do you notice between this and the feature from question 2? Why do you think this is?