4.2 3D Layer Model
Neither of the two important factors described in the previous section can be determined purely from traditional observational approaches. The presence and surface elevation of buried MI inland of the headwall, and thus the OT also, cannot be determined easily without costly and invasive borehole measurements. Similarly, the presence of water rich active layers, and especially thawed soils reaching the massive ice, attenuate the signals from ground penetrating radar, reducing their effectiveness in these environments (Campbell et al., 2018). Passive seismic measurements now offer the potential to spatially map these changes away from the cliff face and hence produce more accurate forecasts of HWR rates.
Using a combination of the surface elevation data, active layer depth measurements and the MI surface model, a 3D layer model was created for the central portion of Peninsula Point (Figure 8a), allowing for a comparison of surface features with internal OT and MI elevation. A fence diagram was also created to allow for a clearer visualisation of the layers used (Figure 8b-e). The middle portion of the model shows a high elevation ice surface, with a thin overburden and an active layer extending down to the MI, with little change extending inland. The OT averages 2.5 m, with a σ of 0.6 m (Figure 8b and Figure 8d). The high ground to the east contains an average OT of 9.0 m and a σ of 1.9 m. The ice and ground surface slowly decrease in elevation inland, resulting in no significant cross-shore trend in OT (Figure 8e). The high ground to the west contains both the most variability in ice surface elevation and OT. The average OT is 10.7 m with a σ of 2.5 m. It contains a large OT range, from 5.3 m to 14.7 m, and contains a distinct bowl-like depression where the ice surface is close to sea level. These substantial variations in MI elevation are not reflected in the surface topography (Figure 8c).