Station PILK

Questions for John Beavan

Pilkington

Plate tectonics is a good model for predicting the large horizontal movements we can measure with GPS on Earth's surface. Not predicted by plate tectonics are vertical motions; those correspond to a number of processes, including erosion and isostatic compensation. Accurate measurements of vertical ground motion are important for resolving the relative importance of these processes.

PILK is located in New Zealand's central Southern Alps (Figure 3). PILK and several other nearby GPS stations were installed by John and his colleagues nearly 15 years ago to measure the growth rate of the Southern Alps. At 3.8 mm/yr the vertical velocity of the site is small compared to typical horizontal motions, but is significant, as the uncertainty is only 0.4 mm/yr. (Compare this vertical rate to some of the other spotlight sites, like P028 and P085.)

Figure 4 shows the uplift rates for PILK and several other stations in the Southern Alps in a profile across the mountain range (Figure 5). Why is PILK going up? The Southern Alps is the site of collision between the Australian and Pacific tectonic plates, and the upward motion of PILK reflects mountain building processes in action at this important collision zone.