Abstract
This article focuses on the quantification of retreat rates, geomorphological processes, and hydroclimatic and environmental drivers responsible for the erosion of an unconsolidated fine-sediment cliff along the north shore of the Gulf of St. Lawrence (Quebec, Canada). Annual monitoring using field markers over a period of twenty years, coupled with photo interpretation and historical archive analysis, indicates an average annual erosion rate of 2.2 m per year between 1948 and 2017. An acceleration in retreat occurred during the last 70 years, leading to a maximum between 1997 and 2017 (3.4 m per year) and 2000–2020 (3.3 m per year). Daily observations based on six monitoring cameras installed along the cliff between 2008 and 2012 allowed the identification of mechanisms and geomorphological processes responsible for cliff retreat. Data analysis reveals seasonal activity peaks during winter and spring, which account for 75% of total erosional events. On an annual basis, cryogenic processes represent 68% of the erosion events observed and subaerial and hydrogeological processes account for 73%. Small-scale processes, such as gelifraction, solifluction, suffosion, debris collapse, and thermoabrasion, as well as mass movement events, such as slides and mudflows, induced rapid cliff retreat. Lithostratigraphy and cliff height exert an important control on erosion rates and retreat modes, which are described by three main drivers (hydrogeologic, cryogenic, and hydrodynamic processes). Critical conditions promoting high erosion rates include the absence of an ice-foot in winter, the absence of snow cover on the cliff face allowing unrestricted solar radiation, the repetition of winter warm spells, snow melting and sediment thawing, and high rainfall conditions (>30 mm or SPI > 2). The relationships between hydroclimatic forcing and retreat rates are difficult to establish without taking into account the quantification of the geomorphological processes involved. The absence of quantitative data on the relative contribution of geomorphological processes can constitute a major obstacle in modeling the retreat of cliffs with regard to climate change.
Highlights
The erosion of coastal cliffs is conditioned by hydrodynamic processes [1,2], and hydrogeologic, gravitational, and cryogenic processes [3,4,5]
This number should be considered as a minimum since only a small part of the coastline was covered by each camera, implying that a far greater number of events occurred simultaneously and independently of our observations. This method allowed us to address the link between all geomorphological processes occurring and the climatic/hydrodynamic conditions throughout the year with a temporal resolution rarely reached in other studies
It highlighted the important role played by environmental variables such as snow cover on the cliff and the presence of an ice-foot, both limiting factors for cryogenic processes
Summary
The erosion of coastal cliffs is conditioned by hydrodynamic processes [1,2], and hydrogeologic, gravitational, and cryogenic processes [3,4,5]. The speed of cliff retreat will depend on hydrometeorological forcing and environmental conditions [12,13], sometimes exacerbated by anthropogenic interventions on the coast, such as sand excavation [14]. Climate-related factors, such as storminess, wind direction, water levels, and wave forcing are crucial environmental drivers in cliff evolution [15]. Non-marine hydrodynamic variables such as rainfall and frost action are important [3,4,17,18]. Parameterization of these other variables into models is still at an embryonic stage, since few studies have attempted to quantify the interrelation between climatic variables
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
