SEASONAL VARIATIONS OF THE GPS SITES OF WHAKAARI VOLCANO, NEW ZEALAND

We have investigated the time series data from continuous GPS measurements located on the Whakaari volcano and the surrounding region at Bay of Plenty in New Zealand. GPS data were obtained by Nevada Magnet Geodetic Global Network Laboratory. We studied the time domain contrast between two periods, one of silence and another of comparatively heightened activity. As with any GPS there are seasonal variations on an annual basis. From May 2016 to July 2018 the seasonal variations on the RGWI station located on the volcano are muted, implying that the seasonal variations are not as noticeable in the measurements from the GPS site stationed on the volcano. Furthermore, the correlation between the north and east vectors were analyzed by applying a moving annual correlation window. The aforementioned annual cycle is increasingly exemplified in the western stations compared to the eastern stations. Conversely, the seasonal variation seems to not have had the same impact on the stations situated on the volcanic island itself. In both stations (RGWI and RGWC), the seasonal variation, which exhibited a consistent trend, became “muted” for an extended period of time. Additionally, we observed that the correlation between the east and north components at RGWC was consistently strong until the months directly preceding the eruption in 2019 during which the correlation became moderate. While the RGWI shows a decreasing trend in the correlation a year preceding the eruption; then the correlation fluctuated indicating a weak association as the eruption approached. RGWC is located at the port of the Whakaari island whereas the RGWI station is location on the peak of the volcano itself.