Lemieux quick clay or leda clay landslide - Canada NRC Unstable Leda Clay & Risk of Sinkholes or Landslides
in Quebec & Eastern Ontario, Canada, Norway, & Sweden
     

  • Quick clay or Leda clay hazards in Quebec & Ontario
    • Clay & unstable soil landslides in Canada, Norway, Sweden
    • Inspecting or soil testing for signs of quick clay or unstable soil
    • Types of sink holes, signs of sink holes or unstable clay soils
    • When to hire a geotechnical engineer for landslide, sinkhole or soil testing
    • Links to Canadian Natural Resources technical articles on unstable clay, quick clay, Leda clay
    • Measuring the strength of frost heaving forces
  • POST a QUESTION or READ FAQs about sinkholes & landslides & the Leda Clay formations in Quebec & Ontario Canada & in Norway & Sweden
  • REFERENCES

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This article describes sinkholes caused by Quick clay or Leda clay hazards in Quebec & Ontario and also discusses the relationship between sinkholes and clay soils causing landslides, soil subsidences, or sudden sinkholes in Canada, Norway, Sweden.

This article series explains what sinkholes are and why they occur, describes their effects on buildings, and gives building and site inspection advice useful in identifying areas where there is an increased risk of sink holes at properties. Synonyms and similar terms for sink holes include: shake hole, swallow hole, swallet, doline, cenote, moulin, and glacier mill, unstable clay soil, Leda clay, or quick clay. The Lemieux landslide photo (left) of an earlier unstable clay soil or quick clay landslide is from the Canadian Department of Natural Resources.

Readers should see SINKHOLES - IMMEDIATE SAFETY ACTIONS, and also see FOUNDATION CRACKS & DAMAGE GUIDE and CESSPOOL SAFETY WARNINGS. Additional septic system safety warnings are at SEPTIC & CESSPOOL SAFETY.

The bare minimum that a property owner needs to know about sinkholes or any other sudden subsidence of soils at a property is that these conditions might be very dangerous. Someone falling into a sink hole or into a collapsing septic tank could be seriously injured or even die. If a suspicious hole, subsidence, or depression appears at a property the owner should rope off and prevent access to the area to prevent anyone from falling into the opening, and then should seek prompt assistance from a qualified expert, geotechnical engineer, septic contractor, excavator, or the like.

Sinkholes hundreds of feet in diameter have occurred in Eastern Canada, Florida, and Texas - big enough to swallow a home. The "December Giant" sinkhole in Montevallo, Alabama was 520 x 125' and 60' deep. The Dasietta Texas sinkhole reached 525' x 600' and a depth of 150', collapsing an era of roughly 1/10 of a square mile within two days of its first appearance.

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Sinkholes in Canada- Leda Clay (Quick Clay) in Quebec & Eastern Ontario, also in Norway & Sweden

Lemieux quick clay or leda clay landslide - Canada NRCUnstable clay soils found in some areas of Quebec and eastern Ontario (also found in Rissa, Norway) can "spontaneously liquefy with little or no provocation", leading to sudden catastrophic sinkhole formation and soil collapse reported the New York Times 13 May 2010).

The Times article reports the tragic death of the Richard Préfontaine family when on May 11, 2010 their home suddenly fell into a mud crater 100 feet deep hole approximately 900 feet by 1700 feet in size. More than 250 such collapses have been identified in this area of Canada.

The Lemieux landslide photo (left) of an earlier unstable clay soil or quick clay landslide is from the Canadian Department of Natural Resources.

The May 2010 Times article explained that because the unstable clay formed in salt water the molecular structure of its particles is unstable (compared with clays formed as layers in fresh water). When an event breaks the molecular bonds between clay particles the clay can spontaneously liquefy.

Quick clay landslide, Surte Sweden 1950  - Wikimedia commonsSkölda et als. reported on the chemistry of unstable clay soils in 2005. In 1950 in Surte, Southwest Sweden, unstable "quick clay" soils led to a catastrophic soil collapse as well. Our photo (left) of the 1950 landslide in Surte is from Wikimedia Commons.

The same Times article reported another clay liquefication collapse in St. Jean Vianney, Quebec in 1971, when 31 people died and 40 homes were destroyed, and continued that the town of Lemieux, Ontario (east of Ottawa) was relocated in 1991 due to concern for unstable clay soils that two years later collapsed over a 42-acre area.

According to Canada's Department of Natural Resources, "The most disastrous Leda clay landslide in eastern Canada occurred in 1908 at Notre-Dame-de-la-Salette, Quebec, with the loss of 33 lives."

This "quick clay" or "Leda clay" found in Quebec and Eastern Ontario is a unique marine clay that can sudden liquefy when disturbed. Quick clay / Leda clay may appear to be solid ground, but it is composed of as much as 80 percent water whose clay particles are held together primarily by the surface tension of water itself.

As for some of the other types and locations of sinkholes discussed here, the presence of un-stable quick clay in Eastern Canada can be detected by soil testing but not by casual inspection of the top layer of (more stable) ground soils. However the long history of more than 100 years of documented sudden subsidences in areas of Quebec has made local experts aware of the risk of this dangerous soil.

Similar unstable clay soils or quick clay found in Rissa, Norway, led to an April 1978 soil collapse covering more than 330,000 squre meters.

Map of quick clay areas in Eastern Canada - Canadian NRCSignificant quick clay or Leda clay collapses in Eastern Canada have been documented in 1908, 1955, 1971, [and April 1978 in Rissa, Norway, 330,000 sq. meters] as well as soil tests (and town relocations) in 1989, 1991, 1993, and the 2010 catastrophe and deaths reported above.

The map (left, from Canada's Natural Resources department in Ottowa) shows the locations of landslides due to Leda clay deposited when the Champlain Sea retreated to its present size, and the blue area on the map shows the maximum extent to which the Champlain Sea previously extended into Eastern Canada.

Part of the explanation underlying the different character of quick clay (Leda clay) in this area of Canada, referred to as marine clay, is the presence of salt (from sea water) that provides sea-salt ions of NaCl acting as an adhesive between the clay particles.

Anatomy of a quick clay landslide - Canada Natural ResourcesIf only the salt were present, the marine clay formed by this process would be quite stable, as it is elsewhere in the world.

The illustration (left, from Canada Natural Resources), shows the "anatomy of a Leda Clay landslide".

But following the retreat of the last glaciers in this area (roughly 10,000 years ago) rainwater in this area (possibly very low in mineral content), perhaps combined with a high silt content of the clay that allowed rainwater to penetrate to the clay layer, resulted in an un-stable clay soil chemistry. -- Wikipedia

Wikipedia adds that "These landslides are progressive, meaning they usually start at a river, and progress upwards at slow walking speed. They have been known to penetrate kilometers inland, and consume everything in their path."

It is not difficult to understand that a soil relying on water's surface tension can easily become unstable in response to even the smallest shock or by a larger one such as an earthquake, even a distant one. The disturbed clay changes form to a watery gel, losing its previously (and false) stable soil characteristic.

Sinkhole Repair Services

Watch out: Readers trying to diagnose and deal with sudden soil subsidence or yard collapses should see SINKHOLES - IMMEDIATE SAFETY ACTIONS.

Companies identify themselves as sinkhole damage repair experts in Floria are listed at SINKHOLE DAMAGE REPAIRS or select a topic from the More Reading links shown below.

More Reading

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