Field Trip Participants. Photo by Marten Geertsema

We will visit the 1993 Lemieux Landslide, a large retrogressive earthflow in sensitive marine clay and silt, on the banks of the South Nation River. If time permits, we will also visit a few of the huge landslides that are thought to have been triggered by a large earthquake circa 4550 yr BP.

Lemieux Landslide

The Lemieux flow, which occurred within the scar of a much earlier rotational slide, rapidly retrogressed 680 m into the surrounding plain. The landslide widened through lateral spreading and subsidence, translation, and rotation of blocks separated from the sidewalls, creating embayments into both the north and south sidewalls. About 2.8 million cubic metres of debris flowed into the river valley, extending 1.6 km upstream and 1.7 km downstream of the crater mouth and completely damming the South Nation River for several days. Presently, only about one-half of this has been eroded away by the river and the deformed structure of the landslide debris can be viewed in sections along the river.

For more information on the Lemieux Landslide, see the attached PDF file [PDF, 12.9 kb, viewer], extracted from a 1997 GACMAC fieldguide.