Welcome to Otuihau - Whangarei Falls waterfall falls over basalt cliffs. The two viewing platforms above the waterfall give spectacular views of the falls and a birds eye view of the forest below. There are a choice of lovely picnic area in the many green spaces.
Basalt is a dark-colored, fine-grained, igneous rock composed mainly of plagioclase and pyroxene minerals. It most commonly forms as an extrusive rock, such as a lava flow, but can also form in small intrusive bodies. It has a composition similar to gabbro. The difference between basalt and gabbro is that basalt is a fine-grained rock while gabbro is a coarse-grained rock.
Most of Earth's basalt is produced at divergent plate boundaries on the mid-ocean ridge system. Here convection currents deliver hot rock from deep in the mantle. This hot rock melts as the divergent boundary pulls apart, and the molten rock erupts onto the sea floor. These submarine fissure eruptions often produce pillow basalts as shown in the image on this page.
During the cooling of a thick lava flow, contractional joints or fractures form. If a flow cools relatively rapidly, significant contraction forces build up. While a flow can shrink in the vertical dimension without fracturing, it cannot easily accommodate shrinking in the horizontal direction unless cracks form; the extensive fracture network that develops results in the formation of columns. These structures are predominantly hexagonal in cross-section, but polygons with three to twelve or more sides can be observed. The size of the columns depends loosely on the rate of cooling; very rapid cooling may result in very small (<1 cm diameter) columns, while slow cooling is more likely to produce large columns.
The active mid-ocean ridges host repeated fissure eruptions. Most of this activity is unnoticed because these boundaries are under great depths of water. At these deep locations, any steam, ash, or gas produced is absorbed by the water column and does not reach the surface. Earthquake activity is the only signal to humans that many of these deep ocean ridge eruptions provide.
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Do not post your answers except the photo.
1. From the platform above the waterfall, you may see a line of bubbles extending from the base of the waterfall. What is causing this?
2. What are two examples to show this is basalt?
3. What do you find along the rocks at the bottom of the waterfall?
4. Which diection is the river flowing? Where does this river end?
5. Upload a photo from the location, include a personal item, gps, or yourself.