Figure 6. Topographic profiles of the west-side-up principal strand of
the Fairweather fault that delineates the western margin of the Kaknau
Creek valley. Profile locations shown in map at upper right; red arrows
point to 20- to 30-m tall scarp formed by principal fault strand. (a)
Tectonic uplift west of the Fairweather fault forms a 20- to 25-m-tall
scarp that elevates and isolates outwash plain deposits above active
stream channel deposits in the Kaknau Creek valley on the east side of
the fault. Secondary scarps near the top of the main fault scarp mark
headscarps of large slope failures or secondary faults related to
oblique slip. (b) Tectonic uplift elevates marine terraces immediately
west of the 25-to-30-m tall Fairweather fault scarp at the mount of
Kaknau Creek. The1958 fault rupture produced ~3 m of
right-lateral slip, but no vertical displacement along this profile.
4.2 Timing of deposition and incision in lower Kaknau Creek Valley
Along the western margin of the Kaknau Creek valley, at a site
informally called the Kaknau Cliff section, periglacial deposits exposed
in ~25-m tall cliffs eroded by the creek (Figure 7)
constrain the initial timing of Terrace B emergence and add insight into
the vertical component of displacement on the Fairweather fault at Icy
Point. Kaknau Creek drains the southwestern corner of the Fairweather
Range, and the west side of the valley, near the mouth of Kaknau Creek,
is bordered by the active Fairweather fault (Figure 4). The Kaknau Cliff
section exposes rhythmically bedded silt and sand deposited in a
proglacial lake and cross-bedded sand deposits formed in a proglacial
delta. Outwash gravel overlying the lake sediment marks the end of
lacustrine deposition (Figure 7). The elevation of the outwash surface
(~50 m) at the Kaknau Cliff section, >25 m
higher than the modern Kaknau Creek channel, implies that the
Fairweather fault steps ~600 m to the east and forms a
25-m tall, linear escarpment toward the northwest (Figures 4 and 6).
Like the modern creek channel, which grades to present sea level, the
highest surface of the outwash plain (Hst), based on its elevation and
slope, was graded to sea level that formed the highest surface
(~46 m) of Terrace B.