Figure 9. Marine terrace elevation profiles; locations shown on index
map at lower left. (a) Elevation profile H–H’ trending northwest
showing relative elevation of Terraces D, C, B and A. The riser between
Terrace C and B is a paleo sea cliff that marks an interval of relative
sea level stasis, when riser height was increased by continued
freshening of the base of the riser through coastal erosion. (b)
Elevation profile I–I’ trending ~N70°E, perpendicular
across the long axes of Terraces D, C, B and A. The highest Kaknau Creek
outwash plain east of Terrace D grades downstream to the highest surface
of marine Terrace B. Red letter F marks active strand of Fairweather
fault. (c) Elevation profile J–J’ trending ~N70°E
perpendicular across the long axes of Terraces C, B and A. (d) Elevation
profile K–K’ trending ~N20W across Terraces B and A.
Arrows in all profiles indicate the direction and length over which
terrace slopes were measured on lidar topography (Witter et al., 2017b).
4.4 Little Ice Age coastal geomorphology reflects glacial rebound
Mann and Streveler (2008) reconstructed post-LGM relative sea-level
change in Icy Strait and documented a high-sea stand during the LIA and
subsequent RSL fall accompanying glacial rebound following 1750 CE. The
geomorphology of Terrace A at Icy Point and the 14C
ages of coastal landforms backing Palma Bay are consistent with the Icy
Strait relative sea-level history. On Terrace A, west of the Fairweather
fault, the age (400–30 cal yr BP, Table 2) of a bivalve shell collected
within beach sand (Figure 10) implies emergence of the terrace surface
within the past few centuries, but broad date uncertainties preclude its
use in the age model (Figure 8). The highest beach ridge along the
landward edge of Terrace A was formed by the LIA high stand and reaches
elevations of 12–14 m (Figures 4 and 10) (Mann and Streveler, 2008).
East of the fault a 12–14 m high, barrier beach ridge fronts the Kaknau
Creek valley along the northern shore of Palma Bay. The crests of the
beach ridge east of the Fairweather fault has a similar elevation as
beach ridge crests backing Terrace A (Figure 10) and both landforms
emerged after 1700 CE, based on spruce forest ages and soil development
(Mann and Streveler, 2008). We infer that these beach ridges on either
side of the Fairweather fault were constructed by ocean waves near the
end of the LIA when RSL was ~4 m higher than present.
The concordance of the beach ridge elevations on either side of Kaknau
Creek (Figure 4) indicate that little or no vertical displacement has
occurred on the Fairweather fault since the marine transgression that
occurred at the height of the LIA, ca. 1750 CE.