This is a relatively easy earthcache that can be completed when travelling either north or south along the Desert Rd. It is easiest and safest to complete when travelling northbound, but with care, can also be completed when travelling southbound. Please see the suggested order of WP visits for northbound and southbound visits below.
Please note that in order to complete this earthcache, you will need a device (GPS unit or phone, etc) that can give elevation/altitude readings. Without this, you will not be able to answer question number 2, and therefore you will not be able to complete this earthcache.
The Rangipo Fault Line
"The most hazardous fault in the Taupo Volcanic Zone" - GNS report for EQC, 2004.
The Rangipo Fault consists of a series of fault lines running approximately N/S through the Rangipo Desert, on the eastern flanks of Mt Ruapehu, in the Central Plateau region of New Zealand's North Island, Te Ika a Maui.
The Rangipo Fault lies approximately 13km east of the Mt Ruapehu creater, and runs for approximately 32 km N/S, predominantly west side down. There are 4 main fault traces, and these are offset from one another by a few km. There are further fault traces NE of the northern end, that may be a continuation of the fault line, and then further north lies the Kaimanawa Fault. The northern end is unclear, and it is possible the fault is up to 43km in length.
Recent studies have produced conflicting estimates of the fault slip rate. A 1998 study suggested that the average slip rate over the last 15000 years was 3mm per year. More recently, in 2004, the slip rate estimate has been refined to just 0.2mm per year over the last 14000 years, and 1.2mm per year for the last 26000 years. While these differing estimates may seem academic, they have a large effect on the considered danger level of the fault line. With approximately 1800 to 2000 years since the last significant rupture event on the fault, and a 3mm per year slip rate, the fault would be considered in a highly dangerous state with the imminent risk of a large earthquake, potentially mangitude 7.5 or more. This would cause widespread devestation for the region.
The revision of the fault slip rate, and investigation results that show the rupturing of the fault line is less often than previously thought, indicates that earthquakes of the order of magnitude of 6 occur around every 3000 years, and magnitude 7 every 11200 to 14000 years.
The abrupt drop in fault slip rate approximately 14000 years ago coincides with the reduction in volcanic activity in the region around the same time. Regardless of the differing fault slip rate estimates however, the fault line is considered dangerous, in that it has historically ruptured producing earthquakes of greater than 7 magnitude in the past.
Earthcache Tasks/Requirements
In order to complete this earthcache and log a "Found It", you will need to undertake tasks and answer three fairly easy questions, listed below. The answers for the questions should be sent to the cache owner, by clicking on "Message this owner" at the top of the cache page - do not post the answers in your found log. The required photo should be posted with your found log - do not send it to the cache owner.
Question 1:
Do not park at Waypoint 1 (published coordinates). Park at the Parking waypoint and walk up the side of the road, outside the barrier. It's only about 150m and it's perfectly safe on the outside of the barrier. Do not walk on the road.
At Waypoint 1 (published coordinates), look across the road at the exposed bank that has resulted from the road cutting. You should be able to see, by looking left and right, that the layers of earth in the bank are relatively uniform, except for at this spot where there is a step change with the layers on the left (North) being a bit higher than those same layers on the right (South). What you are looking at here is the Rangipo Fault line, near ground surface level, where it crosses the road.
The layers may be hard to see, particularly on the right side (South) of the fault. They are quite low down on this side and erosion material has come down and partially obscured them from view. Look further to the right if you need to, in order to see where you expect the layers to be. Don't worry, this is not a university exam or anything, and the point here is to think about what you're looking at rather than perform a PhD level study.
Without crossing the road yourself, please estimate the elevation difference of the corresponding layers - how much they have displaced from one another vertically.
If the fault line moves, as scientists predict, currently an average of 0.2mm per year, how long ago do you believe the layers began to displace against each other? To calculate this, simply divide your vertical displacement estimate by 0.2mm to get the number of years it would take to get the layers shifted as much as they are now.
1. What is your estimate of the vertical displacement of the visible layers in the road cutting, and therefore how long ago do you think the displacement of these layers began?
Question 2:
At Waypoint 2, you are at the elevation of the bottom, or western side, of the fault scarp. Use your GPS unit, phone, or other device, to measure the elevation from sea level here. While here, please see the Additional Task below.
At Waypoint 3, you are at the elevation of the top, or eastern side, of the fault scarp. Use your GPS unit, phone, or other device, to measure the elevation from sea level here.
Calculate the difference between the elevations you measured at Waypoints 2 and 3, and this is the height of the fault scarp.
2. What is the height of the fault scarp?
Question 3:
At Waypoint 4, you are standing on another point where a spur of the Rangipo Fault fault line crosses the Desert Road. The displacement along this fault is much less significant than where the road crosses the fault line around the other Waypoints further south. The fault line here crosses the road in a NNW/SSE direction (almost N/S in fact).
3. Looking towards the NNW direction from the roadside, what evidence can you see of the fault line here across this very flat landscape?
Additional Task:
At Waypoint 2, please take a photo of the fault scarp to the north. Please include in the photo either yourself, part of yourself, your GPS unit, or some other personal (but not too personal) item.
Upload your photo of the fault scarp with your found log.
Once you have completed the tasks, and sent your answers to the cache owner, please go ahead and log your find online - there is no need to wait for confirmation from the cache owner. If there are any issues, the cache owner will be in touch. Please do not forget to upload your photo with your found log - you can do this through the website or the app.
Suggested Order of Waypoint Visits
Northbound:
The safest way to complete this earthcache is to visit the waypoints in the following order while travelling northbound: Waypoint 2, Parking (and walk to Waypoint 1 outside the road barrier on the western side of the road), Waypoint 3, and finally Waypoint 4 (parking for this one is best on the southbound side of the road). These waypoints can mostly be visited by pulling off the left side of the road while travelling in this direction.
Southbound:
The safest way to complete this earthcache when travelling southbound is to visit Waypoint 4 and then go past the others, turn around and complete it in a northbound direction. However, the cache can be completed with care in a southbound direction by visiting the waypoints in the following order: Waypoint 4, Waypoint 3, Parking (carefully pulling into the rest area on the right, then walking to Waypoint 1 outside the road barrier on the western side of the road), and then Waypoint 2. Both the Parking and Waypoint 2 can be accessed while travelling southbound, but extreme care should be taken as this road can be busy at times.