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).