Retrogressive thaw slump activity and related lake colour change in five areas of the western Canadian Arctic

This database contains the spatial coordinates and years (timing and duration) of activity for more than 7400 retrogressive thaw slumps (RTS) in five areas of the western Canadian Arctic covering >150 000 km2. RTS are thermokarst landforms whose headwalls retreat due to thawing of exposed ice-rich permafrost or massive ice at rates that can exceed 10 m per year. Their initiation can relate to rapid ground thaw (e.g., due to a particularly warm summer) or from local erosion undercutting a slope, and once initiated, they may expand for several decades, exporting water, sediment, and dissolved solids downslope or into aquatic systems. The five study areas and their periods of record are: (1) Banks Island (1984-2016), (2) northwest Victoria Island (1984-2018), (3) Bluenose moraine (1984-2018), (4) Paulatuk region (1984-2018), and (5) Richardson Mountains / Peel Plateau (2001-2018). The entries include a code to indicate where each RTS initiated in the landscape (at the coast, on a riverbank, on a lakeshore, or on a slope) and the locations of lakes which changed colour due to RTS activity, and the dates of those changes. The data on new RTS initiations commences one year after the start of record shown above and ends one year earlier than the final date. Some RTS were already active at the start of the record (denoted by the year 1900 in the dataset) and others were still active in the final year of each record (denoted by the year 2100). The RTS activity and lake colour change data were generated from visual observation of Google Earth Timelapse videos (Lewkowicz and Way 2019; Lewkowicz under review) which are mainly derived from Landsat images. Active RTS were identified by the retrogression of their headwalls which appears as movement on the Timelapse videos. The location of the approximate centroid of the RTS was then recorded on Google Earth, together with the dates of activity and the initiation code. The visual identification technique had errors of omission of 8% and of commission (incorrect identification of features as active RTS) of 1% for Banks Island (Lewkowicz and Way 2019). Similar errors are expected for the other four study areas. The activity data are resolved annually, but the year of initiation shown in the database may lag the true date by one year because the Timelapse imagery pre-dated RTS initiation, or because the RTS was too small to be observed in the first year of its existence (Lewkowicz and Way 2019). The date of cessation of activity (if this occurred) may also be subject to a degree of imprecision because it usually takes place gradually over several years, rather than suddenly across the entire headwall. The lakes listed are those that visually changed colour from deep blue to turquoise or beige due to sediment inputs from RTS activity on their shorelines, or up-basin and affecting inflowing rivers or other lakes. The lake data for each study area are provided for the same period as the RTS data. Colour variations not clearly associated with RTS activity were excluded. Lakes reverted to their original colour when RTS activity ceased, or when RTS headwalls receded sufficiently that sediment inputs to the lake declined. Some lakes changed colour more than once and these separate periods were recorded in the database. The use of 1900 and 2100 for dates represents, respectively, lakes that exhibited a colour associated with sediment inputs at the start of the record and those that remained changed at the end of the record. Over 1984-2016, total RTS numbers in the first four study areas increased more than 50 times. The vast majority of the RTS were initiated in association with particularly warm summers (Lewkowicz under review). More than 500 lakes exhibited an altered colour due to inputs of sediment from RTS activity. The complete dataset should be useful for validation of machine-learning techniques which are currently being developed to map RTS and their impacts across the entire Arctic.