The Atnarko complex located in west-central British Columbia comprises pre-Early Jurassic metavolcanic and metasedimentary rocks, termed the Atnarko assemblage, which is structurally interleaved with Late Triassic to Early Cretaceous orthogneiss. The Atnarko assemblage correlates with continental margin assemblages found within the Coast plutonic complex. Tectonic interaction between the Insular and Intermontane superterranes resulted in several phases of deformation including; 1) poorly preserved Jurassic deformation, 2) Early to mid-Cretaceous, southwest to west directed, compression, 3) mid-Cretaceous, north to northeast directed, compression, 4) mid- to Late Cretaceous dextral and sinistral ductile/brittle shearing, and 5) post latest Cretaceous brittle faulting. Peak metamorphism coincides with generation of migmatite in the Early Cretaceous (~117-115 Ma) and is contemporaneous with penetrative ductile fabrics. The Atnarko complex had cooled below 350°C by the Late. Comparison of the Atnarko complex to equivalent portions of the orogen along strike, indicates a post mid-Cretaceous change in structural style. To the northwest the orogen records continued southwest-directed compression which dominates the deformation style; while to the southeast large dextral strike-slip faults dominate. Relative plate motions between ca. 70-60 Ma indicate that dextral transpression occurred between the Kula and North American plates. Strain during this transpressive deformation was partitioned into compressive and translational regions. The Atnarko complex area is situated at the transition between translation and compression. The conditions of the lower and middle crust within the orogen were established by how strain was partitioned across the orogen. The distributed strain also shaped how the orogen responded to Tertiary extension. Continued compression to the northwest of the Atnarko complex led to increased crustal thickness and partial melting of lower and middle crust in the Tertiary. Conversely, the cessation of compression in the southeast lead to a more stable (i.e. cooler) crustal lithosphere. A change in relative plate motions in the early Tertiary triggered full-scale, orogen-perpendicular, collapse in the northwest facilitated by decoupling between the middle and lower crusts along thermally weakened layers. Localized orogen-parallel extension occurred in the southeast which was kinematically linked to large dextral strike-slip faults where the upper crust remained coupled to the middle and lower crust.

The Atnarko complex located in west-central British Columbia comprises pre-Early Jurassic metavolcanic and metasedimentary rocks, termed the Atnarko assemblage, which is structurally interleaved with Late Triassic to Early Cretaceous orthogneiss. The Atnarko assemblage correlates with continental margin assemblages found within the Coast plutonic complex. Tectonic interaction between the Insular and Intermontane superterranes resulted in several phases of deformation including; 1) poorly preserved Jurassic deformation, 2) Early to mid-Cretaceous, southwest to west directed, compression, 3) mid-Cretaceous, north to northeast directed, compression, 4) mid- to Late Cretaceous dextral and sinistral ductile/brittle shearing, and 5) post latest Cretaceous brittle faulting. Peak metamorphism coincides with generation of migmatite in the Early Cretaceous (~117-115 Ma) and is contemporaneous with penetrative ductile fabrics. The Atnarko complex had cooled below 350°C by the Late. Comparison of the Atnarko complex to equivalent portions of the orogen along strike, indicates a post mid-Cretaceous change in structural style. To the northwest the orogen records continued southwest-directed compression which dominates the deformation style; while to the southeast large dextral strike-slip faults dominate. Relative plate motions between ca. 70-60 Ma indicate that dextral transpression occurred between the Kula and North American plates. Strain during this transpressive deformation was partitioned into compressive and translational regions. The Atnarko complex area is situated at the transition between translation and compression. The conditions of the lower and middle crust within the orogen were established by how strain was partitioned across the orogen. The distributed strain also shaped how the orogen responded to Tertiary extension. Continued compression to the northwest of the Atnarko complex led to increased crustal thickness and partial melting of lower and middle crust in the Tertiary. Conversely, the cessation of compression in the southeast lead to a more stable (i.e. cooler) crustal lithosphere. A change in relative plate motions in the early Tertiary triggered full-scale, orogen-perpendicular, collapse in the northwest facilitated by decoupling between the middle and lower crusts along thermally weakened layers. Localized orogen-parallel extension occurred in the southeast which was kinematically linked to large dextral strike-slip faults where the upper crust remained coupled to the middle and lower crust. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

This study is an examination of the rate at which organic debris and clastic sediment accumulate in a gully after it is scoured by a debris torrent. Of particular interest is the effect that a change in land use from old-growth to clear-cut conditions may have on these rates. This change should result in a reduction in the delivery of large organic debris (LOD), which is a major factor in sediment storage in gullies. It is hypothesized that this change in land use, and the subsequent reduction in the LOD supply, should result in a significant difference in debris recharge rates between old-growth and clear-cut gullies. Twenty-nine gullies in both land-treatment groups were sampled on the west coast of the Queen Charlotte Islands. Sampling procedures involved the estimation of the volume of LOD and sediment in storage (normalized by the gully surface area) and the determination of the time elapsed since the last debris torrent. These data were then used to estimate recharge rates(3h1)am’year of LOD, sediment, and total debris. Recharge rates of each material were compared between land-treatment groups using the nonparametric Mann-Whitney test. This test revealed that LOD has been delivered to old-growth gullies at a significantly higher rate relative to clear-cut gullies. There was no significant difference in sediment and total debris recharge rates between gullies in the two groups, but this outcome was partially a result of the small samples and the different debris recharge times in each data set. Graphical representations of the data permitted the identification of possible temporal trends in sediment and debris accumulation, which may be strengthened with larger data sets. Debris recharge rates have several applications. The estimate of sediment volume stored in a gully can be used in the construction of local sediment budgets, as one component of a watershed sediment cascade is quantified. The calculation of debris recharge rates will provide insight into the transfer rate of sediment from hillslopes to low order channels and to the storage capacity of the channels. Finally, debris recharge rates can be used to improve knowledge of the frequency-magnitude characteristics of debris torrents in an area.

This study is an examination of the rate at which organic debris and clastic sediment accumulate in a gully after it is scoured by a debris torrent. Of particular interest is the effect that a change in land use from old-growth to clear-cut conditions may have on these rates. This change should result in a reduction in the delivery of large organic debris (LOD), which is a major factor in sediment storage in gullies. It is hypothesized that this change in land use, and the subsequent reduction in the LOD supply, should result in a significant difference in debris recharge rates between old-growth and clear-cut gullies. Twenty-nine gullies in both land-treatment groups were sampled on the west coast of the Queen Charlotte Islands. Sampling procedures involved the estimation of the volume of LOD and sediment in storage (normalized by the gully surface area) and the determination of the time elapsed since the last debris torrent. These data were then used to estimate recharge rates(3h1)am’year of LOD, sediment, and total debris. Recharge rates of each material were compared between land-treatment groups using the nonparametric Mann-Whitney test. This test revealed that LOD has been delivered to old-growth gullies at a significantly higher rate relative to clear-cut gullies. There was no significant difference in sediment and total debris recharge rates between gullies in the two groups, but this outcome was partially a result of the small samples and the different debris recharge times in each data set. Graphical representations of the data permitted the identification of possible temporal trends in sediment and debris accumulation, which may be strengthened with larger data sets. Debris recharge rates have several applications. The estimate of sediment volume stored in a gully can be used in the construction of local sediment budgets, as one component of a watershed sediment cascade is quantified. The calculation of debris recharge rates will provide insight into the transfer rate of sediment from hillslopes to low order channels and to the storage capacity of the channels. Finally, debris recharge rates can be used to improve knowledge of the frequency-magnitude characteristics of debris torrents in an area. / Arts, Faculty of / Geography, Department of / Graduate

Moraine and glacier dams bordering the Homathko Icefield burst in the 1980s and 1990s, causing catastrophic downstream floods. The largest of the floods occurred in August 1997 and was caused by rapid breaching of the dam that impounds Queen Bess Lake, below Diadem Glacier. The outburst flood from the lake eroded the Holocene-age sediment fill in the valley below, exposing a series of subfossil forest layers separated by overbank floodplain sediments. A field investigation of the eroded valley fill in 2008 revealed multiple paraglacial valley-fill units, many of which are capped by in situ stumps and woody detritus. Dendrogeomorphic dating and stratigraphic evidence revealed six major sediment deposition events that coincide with regional, independently dated glacier episodes over the past 1200 years. Construction of tree-ring chronologies for the study area also allowed for the examination of the relationship between radial tree growth and hydroclimate. Dendroclimatological and dendrohydrological techniques were used to reconstruct summer stream discharge of nearby Chilko River. An Engelmann spruce tree-ring chronology provided a proxy for mean summer discharge of Chilko River for the period 1775-2007. This record is the first to be developed from tree-ring data for a river draining a glacierized watershed in the British Columbia Coast Mountains. This proxy record provides insights into streamflow variability of a typical Coast Mountains river over the past 232 years and confirms the long-term influence of the Pacific Decadal Oscillation and El Niño-Southern Oscillation teleconnections on hydroclimatic regimes in the region.