Anatomy of the Kitimat fiord system, British Columbia

Abstract The geomorphic complexity of the Kitimat fiord system, on the active margin of British Columbia, Canada, is analysed from several perspectives. Sub-glacial landforms and sediments show that grounded ice exiting the fiord system at the last glacial maximum streamed down Moresby Trough towards the Queen Charlotte trough mouth fan. After brief halts on the inner shelf, grounded ice margins cleared the fiord threshold perhaps by c. 15.5 ka cal. yrs BP, and certainly before 13 ka cal. yrs BP. Just outside the fiords, meltwater plumes deposited stratified glaciomarine sediments interbedded with submarine slides. Inside the fiords, thick glaciomarine sediments were deposited, and large transverse moraines formed during temporary halts in retreat. Several glacial outburst floods eroded the Kitkiata moraine and deposited distinctive mud deposits. Postglacial sedimentation on fiord floors has been spatially variable: drifts of mud > 90 m-thick corresponding with areas of low current velocity alternate with areas of non-deposition and erosion corresponding with areas of high velocity. The fiord system hosts more than a hundred morphologically diverse fan deltas that can be classified in the Prior and Bornhold (1989, 1990) system. Submarine mass transport was most frequent immediately following ice retreat (15.5–11.5 ka cal. yrs BP). The largest event (~ 1.2 km 3 ) involved failure of glaciomarine sediment on a submarine moraine at Squally Channel, and consequent movement of material into the adjacent deep basin. This event occurred post-13 ka cal. yrs BP. In the postglacial phase, mass transport continued on a lesser scale up to the present day, most intensively in Kitimat Arm. From the perspective of glacial landforms, postglacial sedimentation and mass transport, this Pacific active margin fiord system has some parallels with fiord systems on Canada's east coast passive margin, and with Norwegian fiords, but the intensive development of Holocene fan deltas is strongly distinctive.