Prior to European settlement, the Upper Hunter River near Muswellbrook, New SouthWales, was a passively meandering gravel-bed river of moderate sinuosity and relatively uniform channel width. Analyses of floodplain sedimentology, archival records, parish maps and aerial photographs document marked spatial variability in the pattern of channel change since European settlement in the 1820s. Different types, rates and extents of change are reported for seven zones of adjustment along an 8 km study reach. This variable adjustment reflects imposed antecedent controls (buried terrace material and bedrock), which have significantly influenced local variability in river sensitivity to change, as well as contemporary morphodynamics and geomorphic complexity. Local variability in system responses to disturbance has important implications for future river management and rehabilitation.Lagged response and variability in the timing and magnitude of channel adjustment to imposed disturbances are persistent themes in fluvial geomorphology. Lagged response to disturbance is often explained in terms of the recurrence of floods of a given magnitude and duration that exceed the threshold conditions lowered by a disturbance (see, e.g., Schumm, 1979). It can also be examined in the context of a sequence of floods that magnifies the response of individual floods (Costa and O'Connor, 1995;Nanson, 1986;Newson, 1980). In south-eastern Australia multi-decadal cycles in the flood regime, known as flood and drought dominated regimes (FDRs and DDRs), have been invoked to explain channel change in some rivers (Erskine and Warner, 1988;Warner, 1987). While it has been demonstrated that these secular climatic phases do not represent the ultimate cause of channel metamorphosis in south-eastern Australia over the last 200 years Brierley, 1997, 2000;Brooks et al., 2003), they may account for lagged responses, particularly in circumstances where the disturbance occurs within a DDR and several decades pass before floods of an appropriate magnitude cause the necessary threshold exceedance and geomorphic response. Furthermore, there is little doubt that in the post-disturbance period such flood and drought phases exert a strong bearing on channel morphodynamics.It is now clear that European settlement of Australia in the late 18th and early 19th centuries significantly altered fluvial dynamics in many rivers (Brooks and Brierley, 1997;Olley and Wasson, 2003;Prosser et al., 2001). For 2000 years prior to European settlement rivers in coastal south-eastern Australia were characterized by relative geomorphic stability (Nanson and Doyle, 1999). Large scale channel adjustments such as lateral migration were rare and overbank deposition of fine material dominated (Rustomji et al., 2006). Hydraulic roughness was high as a result of well vegetated riparian zones and instream large woody debris (Brooks et al., 2003). Following European settlement, unprecedented channel change resulted from a combination of riparian vegetation and wood removal Brooks and Brier...
Whereas the coast of Peru south of 10°S is historically accustomed to tsunamigenic earthquakes, the subduction zone north of 10°S has been relatively quiet. On 21 February 1996 at 21:51 GMT (07:51 local time) a large, tsunamigenic earthquake (Harvard estimate M w 7.5) struck at 9.6°S, 79.6°W, approximately 130 km off the northern coast of Peru, north of the intersection of the Mendaña fracture zone with the Peru-Chile trench. The likely mechanism inferred from seismic data is a low-angle thrust consistent with subduction of the Nazca Plate beneath the South American plate, with relatively slow rupture characteristics. Approximately one hour after the main shock, a damaging tsunami reached the Peruvian coast, resulting in twelve deaths. We report survey measurements, from 7.7°S to 11°S, on maximum runup (2-5 m, between 8 and 10°S), maximum inundation distances, which exceeded 500 m, and tsunami sediment deposition patterns. Observations and numerical simulations show that the hydrodynamic characteristics of this event resemble those of the 1992 Nicaragua tsunami. Differences in climate, vegetation and population make these two tsunamis seem more different than they were.This 1996 Chimbote event was the first large (M w \7) subduction-zone (interplate) earthquake between about 8 and 10°S, in Peru, since the 17th century, and bears resemblance to the 1960 (M w 7.6) event at 6.8°S. Together these two events are apparently the only large subduction-zone earthquakes in northern Peru since 1619 (est. latitude 8°S, est. M w 7.8); these two tsunamis also each produced more fatalities than any other tsunami in Peru since the 18th century. We concur with WIENS (1990, 1992) that this subduction zone, in northern Peru, resembles others where the subduction zone is only weakly coupled, and convergence is largely aseismic. Subduction-zone earthquakes, when they occur, are slow, commonly shallow, and originate far from shore (near the tip of the wedge). Thus they are weakly felt, and the ensuing tsunamis are unanticipated by local populations. Although perhaps a borderline case, the Chimbote tsunami clearly is another wake-up example of a ''tsunami earthquake.''
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TABLE I1 THE CONDUCTIVITY OF AQUEOUS POTASSIUM HYDRO-FLUORIDE AT 25 ' c 0.020 0.006 0 . m 5 0.002 0.001 A exptl. 138 150 167 217 270 A calcd. 136.0 163.3 169.fi 217.7 265.5 yo Dev.
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