Search

The 1889 rock slide along Champlain Street is the one that caused the largest number of fatalities in this area of Québec City during the 19th century. This paper presents a historical retrospective of the events leading to the 1889 slide, starting with the 1841 slide in the same area, which was as significant. Mitigation measures were initiated mainly after 1880, but they were not sufficient to prevent the major catastrophe anticipated by those who did the investigation of the Cap Diamant, including Charles Baillairgé. The story of the 1889 slide ends in 1894 by a judgment by the Supreme Court of Canada, in which the Queen was not held responsible for the consequences of the slide, although the main trigger was the water draining from the Citadel, from a damaged drain, into the cliff fissures. A back-analysis of the 1889 slide reached the same conclusions as Charles Baillairgé: the 1889 slide was a topple. This paper also highlights the significant contribution of Charles Baillairgé (1826–1906) in the understanding of rock slide processes along Cap Diamant. [ABSTRACT FROM AUTHOR]

The earthquake that occured on 5 February 1663 is the first strong historical earthquake recorded in Canada and is currently estimated to have been located near La Malbaie and to have had a magnitude M of about 7. It left various signatures in the landscape that reveal its extent and significance. In the terrestrial domain, landslides were observed in various regions of Quebec, including Betsiamites, Saguenay, Charlevoix, and Mauricie. In the subaqueous domain, related mass movements were found along the St. Lawrence Estuary, the Saguenay Fjord, and various lakes on the Canadian Shield and likely also in the Appalachian. The minimum cumulative volume of mass movements associated with the 1663 earthquake is 1.7 km3. From the analysis of landslide-related data and using empirical methods for magnitude estimation, the position of the epicentre would be located in the Canadian Shield to the north of the St. Lawrence River with a minimum magnitude M of 7.2 ± 0.2 and a maximum magnitude that would be close to the maximum for the Charlevoix area, which has been previously estimated at M = 7.8 ± 0.6. [ABSTRACT FROM AUTHOR]

In 1996, following torrential rains, a layer of clean sediments was deposited in the upstream part of the Saguenay Fjord. This layer acted as a damping layer between contaminated sediments and the Saguenay waters. It is important to collect information on the water–sediments interface, which is the site of exchanges between the sediments and the waters. Three oceanographical campaigns have allowed us to obtain the data on the velocity of the benthic currents and the properties of the surface sediments. The velocities have been obtained by means of two current meters located at 3 m from the bottom and by means of registered videos. These two types of measurements have given comparable results. The main information collected on the sediments were their water content, grain size, density, and the presence of benthic fauna. The distribution of the main biogenic structure, the tubes of polychetes, is related to the depth of the site and to the grain size of the sediments. For the surface layer, large variations of the water content were obtained during the field measurements. Tests with an axial tomodensitometer have revealed a large variation in the density of the sediments in the top 2.5 cm. [ABSTRACT FROM AUTHOR]

In July 1996, a flash flood resulted in the input of 9 million m³ of sediment toward the Bay of Ha! Ha!, leading to the elimination, partly or totally, of the benthic fauna of the bay. In this study, the CT scanner has been used in a highly perturbed environment, the Bay of Ha! Ha!, to both assess (i) the relationships between the variations of tomographic intensities and the sedimentologic parameters of the sedimentary column and (ii) to quantify the biogenic structures resulting from the activity of benthic organisms. Compaction, CaCO[sub3] contents, and granulometry of sediments are the most important influences on the variation of tomographic intensities. The scanner allowed the study and quantification, in a non destructive way, of the sediment occupation by biogenic structures and, more particularly, allowed to further assess most of the relative importance of the fine fraction of biogenic structures (0.250-1 mm) in the surface sediment layer (0-5 cm). Sediment occupation by biogenic structures reached maximal values at the upper part of the sedimentary column and decreased with depth. If sedimentary reworking leads to an increase in the sediment porosity, destabilization generated by the activity of organisms is balanced by the consolidation of the wall of the biogenic structures. Bioturbation resulting from the activity of benthic organisms into the sediments has a significant role on the sedimentary structure and biogeochemical processes. It is therefore necessary to quantify the volume of sediments occupied by biogenic structures to assess the activity of benthic organisms in the sedimentary column. [ABSTRACT FROM AUTHOR]

Following the flood of July 1996, a significant quantity of sediment, coming from the catchment areas contiguous to the Saguenay fjord, was discharged in the Baie des Ha! Ha! and the North Arm. To characterize the mode of deposit and the potential for remobilization of these deposits, a series of cores was taken in the fjord using a box corer and a gravity corer during the summers of 1997 and 1998. These cores have been analyzed by the axial tomodensitometer at the Regional Hospital Center of Rimouski. The use of the tomodensitometer in geology allows a nondestructive study of the sample and a qualitative and quantitative evaluation of the density of the sediments, their mode of deposition, and their compaction. The study of the upper 45 cm of sediments shows the presence, in the uppermost layer, of several facies type characteristics of a gravity deposit. This layer rests on an erosional unconformity cut into the surface of the older deposits, themselves of gravity type. One year after the flood, no trace of reworking could be detected in the upper part of the cores. Nevertheless, cores taken in the summer of 1998 show a significant reworking of the superficial sediments in direct relation with bioturbation. No reworking of hydrodynamic origin was observed.Key words: scanography, flood, turbidity currents, sedimentary structures, compaction, bioturbation.Suite aux crues de juillet 1996, une importante quantité de sédiment provenant des bassins versants contigus au fjord Saguenay s'est déversée dans la baie des Ha! Ha! et dans le bras nord. Afin de caractériser le mode de mise en place et le potentiel de remobilisation de ces dépôts, une série de carottes a été prélevée, dans le fjord, à l'aide d'un carottier-boîte et d'un carottier à gravité durant l'été 1997 et 1998. Ces carottes ont été analysées à l'aide du tomodensitomètre axial du Centre Hospitalier Régional de Rimouski. L'utilisation du scanographe (ou tomodensitomètre) permet une évaluation qualitative et quantitative de la densité des sédiments, de leur mode de mise en place et de leur état de compaction. Les 45 cm supérieurs des dépôts représentent, dans la couche nouvellement déposée, plusieurs types de faciès caractéristiques d'un mode de dépôt gravitaire. La base de cette couche repose en discordance érosionelle sur des dépôts plus anciens de même type. Un an après la crue, aucune structure superficielle de remaniement n'a pu être décelée dans la partie sommitale des carottes. Néanmoins, des carottes prélevées en été 1998 montrent un remaniement important des sédiments de surface en relation directe avec la bioturbation. Aucun remaniement d'origine hydrodynamique n'a été observé.Mots clés : scanographie, crue, turbidites, structures sédimentaires, compaction, bioturbation. [ABSTRACT FROM AUTHOR]