The Track
Start: 250m up the road from the Whakapapa Visitor Centre
Distance: 7km
Time: 2.5 hours return
This is an easy tramping track that can be walked in either direction, but I would recommend starting at the bottom (near the visitor center and walking up, returning via Bruce road). The track first meanders through mountain beech forest along a cascading stream opening up to swamp, tussock and subalpine plant country, before arriving at the rapids. You will get great views of Mt. Ruapehu and Mt. Ngauruhoe (a.k.a Mt. Doom) on a clear day.
Know before you go – tell someone your plans, check the weather forecast and track conditions. Tongariro National Park weather is extremely changeable all year round. Be prepared for cold, wet windy conditions. Take adequate clothing (warm, water- and wind proof layers), comfortable shoes or boots, something to eat and drink, sunglasses and sunscreen, and a first aid kit.
What causes the Silica Rapids?
Rain water and snow melt seeps into the ground and sinks deeper and deeper through fissures in the rocks. It gets so deep that it is heated by an underlying reservoir of hot rock and it picks up gas escaping from the molten rock (magma) below. The hot water (now buoyant) rises along a fault or large crack and along the way it reacts with the surrounding andesitic rock and absorbs minerals (particularly silicate and aluminium). Finally it bubbles up to the surface through a spring at the base of a lava flow further up the valley.
Gassy, silica/aluminium-rich water pours out of the spring. Gas starts to escape and the minerals become less soluble and are left behind on the rocky surfaces of the stream. The more turbulent the flow, the more gas is lost and the more mineral deposit is left on the rocks. These deposits give the rapids their creamy-white appearance.
The Earth Cache
To complete this earth cache please email me the answers to the following questions (include your username and the name of this cache). Please do not post answers in your log but feel free to add a picture of yourself/your GPS or interesting point along the walk (do not include spoilers). You may log your find as soon as you have emailed the answers to me i.e. you do not need to wait for permission. I will be checking logs and email you if there is a problem. Please no cheating it just spoils it!
Question 1. Waypoint R1 Golden Rapids: Which two sediments in the stream bed causes the difference in colour at this point?
Question 2. Waypoint R2 Rocks: What rocks are described in this area?
Question 3. Waypoint R3 Silica Rapids: Turbulent flow at this point in the stream causes more gas to be lost thus speeding up mineral deposition. Up to how many cm thick is the creamy white alumino-silicate deposit in this area?
All answers can be found on the information signs at the marked waypoints. Please respect the area, do not leave the track and take all rubbish home with you. Happy Earth Caching!