Dr. George D. BATHRELLOS Dr. Hariklia D. SKILODIMOU

Landslides

A recurrent phenomenon

environment

Relief is a component of the Environment

Geomorphology is the scientific discipline, which study and research the relief, the landforms, their genesis and formation, their evolution and the processes that form or change them

Meteora, Central Greece Santorini Island

• is a component of the environment

• nowadays is trying to imposed on the environment and creates structures or constructions, which are serving him

man

Attiki odos, Athens,Greece

Metropolitan area of Athens

natural environment

interactive

relationship

⇔

• In human attempt to impose on the environment, the environment reacted

• Human activities affect the natural processes and / but

Natural phenomena sometimes destroy the human constructions

• D. Coates: In the urban environment, man is the creator of the landscape or “cityscape”

-manmade built

environment - human activities

Geomorphic Hazards can be regarded as the group of threats to human resources resulting from the instability of the Earth’s surface features. The importance of these features is concentrated on the response of the landforms to the processes, rather than on their original source (Gares et al., 1994) .

Geomorphic Hazards can be categorized as endogenous (volcanism and neotectonics), exogenous (floods, karst collapse, snow avalanche, channel erosion, sedimentation, mass movement, tsunamis, coastal erosion), and those induced by climate and land-use change (desertification, permafrost, degradation, soil erosion, salinization, floods) (Slaymaker, 1996).

Often when a natural disaster occurs, some others contemporary or/and subsequent catastrophic phenomena are occurred, which cause always small or big changes in the relief and sometimes widespread economic and social impacts.

E.g. Earthquake → Landslides, Submarine earthquake → Tsunamis, Erosion or/and floods → Landslides

Geomorphic Hazards

What is a Landslide?

Landslide is a Geomorphic Hazard. Landslide is a general term used to describe the down-slope movement of soil, rock, and organic materials under the effects of gravity and also the landform that results from such movement (Highland & Bobrowsky, 2008). Mass movements are the result of shear stresses on slopes (caused by gravity, the weight of material and soil water) overcoming the inherent resistance of the materials (made up of the cohesive properties of slope particles and their internal friction) (Hart, 1986). In general, the scientists use many terms worldwide for this phenomenon, such as “landslide”, “landslide events”, “mass movements”, “mass-wasting”, “gravity movements” and “slope movements” (Terzaghi, 1950; Coates, 1977; Varnes, 1978).

• Gravity on a flat surface on an inclined plane As much as greater is the slope, so much greater is the force, that causes movement (gt)

Τ Τ

What about - the Friction and

- the Sliding surface (soil, sand, clay);;;

What does Landslides cause?

(modified from Nelson, 2013)

Water as causative factor

(modified from Nelson, 2013)

Dry unconsolidated grains Slightly wet unconsolidated materials

Saturated material

Natural and anthropogenic undercuts

Many other causative factors, that cause mass movements (landslides), are reported in the scientific literature. These parameters are: •Lithology. •Land uses. •Tectonic elements. •Slope angle, •Slope aspect. •Geometry of main discontinuities •Anthropogenic activities •Hydrographic (drainage) network. •Etc, etc, etc.

Other causative parameters

• rainfall,

• earthquakes and

•human activities

Triggering factors

The worldwide most used classification is that USGS (2004) and Varnes (1978) have proposed. According to Varnes (1978) the types of movements are: fall, topple, slide, spread and flow.

Which are the mass movements (landslides) types?

USGS (2004)

Which are the parts of a landslide?

Source: http://www.oas.org/dsd/publications/Unit/oea66e/p305.GIF

Where are the recorded Landslide Phenomena in Hellas?

In Hellas, landslides are usual in Flysch formations (30.35%), Neogene sediments (28.20%) and Loose Quaternary deposits (20.65%). In western Hellas, landslides are usual because of intense rainfall.

Landslide in flysch formations and debris falls in Koziakas Mt.

Landslides are independent or related phenomena?

The landslides events usually accompany or / and follow other catastrophic events, as earthquakes, intense rainfall, erosion, etc.

The 1999 multi-hazard event in Tanaguarena, in coastal Venezuela, South America. The floods and landslides were triggered by heavy rains. (photograph by Matthew Larsen, U.S. Geological Survey)

Bluebird Canyon landslide (USA) The October 2, 1978 Bluebird Canyon landslide in Orange CountyCalifornia cost, $52.7 million (2000 dollars) 60 houses destroyed or damaged. Unusually heavy rains in March of 1978 may have contributed to initiation of the landslide. Although the 1978 slide area was approximately 3.5 acres, it is suspected to be a portion of a larger, ancient landslide. A large, translational landslide, called the Laguna Beach, CA landslide occurred in June, 2005. This landslide severely damaged or destroyed 19 homes, and resulted in the evacuation of 345 homes. There were no serious injuries or loss of life. The 2005 landslide is located about 200 feet east of the 1978 Bluebird Canyon landslide.

Is there Continuity or Repetition in Landslide Phenomena?

Source USGS [http://landslides.usgs.gov/learn/photos/california__u.s._/laguna_beach_and_blue_bird__ca_landslides]

Source USGS [http://landslides.usgs.gov/learn/photos/california__u.s._/laguna_beach_and_blue_bird__ca_landslides]

Source USGS [http://landslides.usgs.gov/learn/photos/california__u.s._/laguna_beach_and_blue_bird__ca_landslides]

Source USGS [http://landslides.usgs.gov/learn/photos/california__u.s._/laguna_beach_and_blue_bird__ca_landslides]

La Concita, CA (USA)

1995

2005

Source USGS [http://landslides.usgs.gov/learn/photos/california__u.s._/la_conchita__ca__1995]

2005

Source USGS [http://landslides.usgs.gov/learn/photos/california__u.s._/the_2005_la_conchita__california_landslide]

Source USGS [http://landslides.usgs.gov/learn/photos/california__u.s._/the_2005_la_conchita__california_landslide]

Landslide Phenomena are usually characterized from continuity or repetition. Recurrence of landslides is controlled by the repetition of triggering factors (rainfall, earthquakes, etc). Characteristic phenomenon of Landslide Recurrence or Landslide Reactivation in Hellas has been recorded in Ropoto village (Trikala Prefecture, Central Greece). Landslides events had been catalogued in the winters of the years:

• 1962 – 1963, • 1975 – 1976, • 1978 – 1979, • 1990 – 1991, • 1993 – 1994, • 2009 – 2010 and • 2011 – 2012

An over 50 years landslide in Hellas

Landslides events during the winters of

1962–1963 (not available photographs from this event)

1975–1976 (not available photographs from this event)

1978–1979

Landslides events during the winters of

1990–1991 (not available photographs from this event)

1993–1994

Landslides events during the winter of 2009-2010

Landslides events during the winters of 2011-2012

2010 2012

2010 2012

2010

2012

Settlements situated on palaeo-landslides

Panagia (Trikala Pr., Central Hellas)

Panagia (Trikala Pr., Central Hellas)

Pyra (Trikala Pr., Central Hellas)

Exercises

• Identify and draw the rock and debris falls on the satellite image. The satellite image was taken from Google Earth. The study area is located in Koziakas Mt (Trikala Prefecture, Central Greece).

•Evaluate and draw the possible initial (starting) position of rock and debris on the same satellite image.

•In what type of geological formations the rock falls are usually manifested?

• Draw the landslide outline on the lower satellite image. • On the same satellite image, draw

a. the "surface of separation", b. the "zone of depletion", and c. the "zone of accumulation" of the landslide.

• From the above photograph, evaluate how many stages of landslide evolution we can record.

• Draw on this photograph the stages of landslide manifestation.

• In the satellite image, recognize and draw at least one active landslide and one palaeo-landslide (inactive landslide). Use the differences in land uses (vegetation cover) and the characteristic shape of the landslide.

• In the longitudinal section, draw the shape of a possible future landslide. Mark the zones of depletion and accumulation.

• Which should be the impacts to the settlement? • Calculate the slope of the hillside, if the altitude difference between the y and y'

is 235m and distance between the Δ and A is 400m.

• In the following sketches, determine (i)what potential mass movement hazards exist, (ii) why these hazards exist, and (iii) what might be done to mitigate the hazard or remove the danger (Nelson, 2013).

- Alcántara-Ayala, I., 2002. Geomorphology, natural hazards, vulnerability and prevention of natural hazards in developing countries. Geomorphology 47, 107–124.

- Coates, D.R., 1977. Landslide prospectives. In: Coates, D.R. (Ed.) Landslides, Geological Society of America.

- Gares, P.A., Sherman, D.J., Nordstrom, K.F., 1994. Geomorphology and natural hazards. Geomorphology 10, 1– 18.

- Hart, M.G., 1986. Geomorphology, Pure and Applied. Allen & Unwin Ltd. - Highland, L.M., Bobrowsky, P., 2008. The landslide handbook—A guide to understanding

landslides: Reston, Virginia, U.S. Geological Survey Circular 1325, 129 p. - Nelson, S.A., 2013. Slope Stability, Triggering Events, Mass Movement Hazards. EENS 3050,

Natural Disasters, Tulane University, http://www.tulane.edu/~sanelson/Natural_Disasters/slopestability.pdf

- Slaymaker, O., 1996. Introduction. In: Slaymaker, O. (Ed.), Geomorphic Hazards. Wiley, Chichester, pp. 1 –7.

- Terzaghi, K., 1950. Mechanism of Landslides. In: Berkel (Ed.) Engineering Geology, The Geological Society of America.

- USGS (2004): Landslide Types and Processes. U.S. Department of the Interior. Fact Sheet 2004-3072 [available http://pubs.usgs.gov/fs/2004/3072/].

- Varnes, D.J., 1978. Slope movement types and processes. In: Schuster, R.L. & Krizek, R.J. (eds) Landslides, analysis and control. National Research Council, Washington, D.C., Transportation Research Board Special Report 176, p. 11–33.

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