Monitoring and physical model simulation of a complex slope deformation in neovolcanics

1. Institute of Rock Structure and Mechanics Czech Academy of Science Prague, Czech Republic Monitoring andphysical model simulation of a complex slope deformation in neovolcanics J. Rybá ř &B. Koš ť ák

2. Čeřeniště landslide – the main scarp

3. Čeřeniště slide - upper part displays individual blocks separated by deep trenches

4. Čeřeniště slide – situation of slope deformations 1- scarps and trenches in basalt rocks 2 - recent potential and old landslides 3 – recent active landslide 4 - outstanding edges in the relief 5 - erosional walls 6 - debris 7 - alluvial sediments 8 - spring 9 - lake 10 - undrained depressions 11 - waterflow 12 - periodically dry creek

5. C r o s s s e c t i o n: Strange tilted platformwith a lake The Labe River Canyon 2km: 140 m a.s.l. Čeřeniště slide - geological cross-section through the slope deformation

6. I n v e s t i g a t i o n m e t h o d s: Engineering-geological maps - scale 1:2 000, 1:5 000 - geomorphological and geological maps 1:10 000 - series of longitudinal and transversal profiles Monitoring of deformation effects - two highly sensitive mechanico-optical dilatometric gauges TM71 in the trenches under main separation wall Applied geophysics - three phases: - symmetrical resistance profiling and vertical electrical probing - spontaneous polarisation SP - radiometry Geomorphological investigations - to find relation between the evolution of the Labe River valley and Čeřeniště slope deformations Geological and Quarterly-geology methods and dendrochronology Photoplastic physical models- to verify the solutions

7. Čeřeniště slide - 3D field deformation monitoring in scarps using TM71

8. Monitoring: • Displacements registered at the upper partof • Čeřeniště deformation • Component z  represents progressive sinking • of rock blocks into the main scar trench • No separation of rock blocks indicated • Low value angular deviations registered provide evidence of block arching in scar zone

9. P h o t o p l a s t i c m o d e l s: • made of agar gels: • agar deforms progressively by body weight after horizontal sidewise stress release • models are observed in polarized light • models produced as a series of individual elastoplastic, brittle layers with slippery plastic intercallations • following model is simulating a series of basalt lava flows with tuff intercallations in a deformation process of gravitation tectonics induced by deepening of the Labe River Canyon • the erosion process took place in Pleistocene when volcanites were cut through completely up to the Cretaceous basement - the Labe River reached then a level of up to 16 m beneath the present bottom (140 m a. s. l.)

10. P h o t o p l a s t i c m o d e l Upper scar area of the Čeřeniště landslide produced in one of the models • Morphology shows: • separation wall • deep scar • inclined sinking blocks • trenches in the marginal zone (right) • voids under the hill (left)

11. P h o t o p l a s t i c m o d e l • complex layered model representing a series of lava flows • deepening of the Labe River Canyon • formation of wedge-like islands separated by anticlinal shear planes after horizontal stress release • the wedge-like islands are almost stress free • chance for undisturbed platforms to develop and survive in the heavily deformed slope platform formation

12. P h o t o p l a s t i c m o d e l Model 30: Evolution in a system of volcanic lava flows after a unilateral deformation release due to the Labe River erosionmodel time: 0:10:00

13. P h o t o p l a s t i c m o d e l Model 30: Superficial block morphology in the scar area due to continuing evolution in the system of lava flows in the unilatreal release process due to the Labe River erosionmodel time: 0:30:00

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17. The END... ...thanks for your attention!