J. Blahut

Analysis of rainfall preceding debris flows on the Smědavská hora Mt., Jizerské hory Mts., Czech Republic

In August 2010, extreme rainfall affected the north of the Czech Republic and caused regional floods and landslides. Three torrential debris flows originated in the Jizerské hory Mts., close to Bílý Potok on the north slope of the Smědavská hora Mt. The rainfall situation which triggered the debris flow was analyzed and compared with the rainfall situation in 1958 when a debris flow occurred in the same area. The rainfall data were obtained from rain gauges of the Czech Hydrometeorological Institute. Four rain gauges were chosen close to the Smědavská hora Mt. with data of daily amounts from 1983 to 2013 and 10-min intensity or hourly amounts from the specific period. The data from 1958 were available from three different rain gauges (only daily amounts). The data series were not complete so linear regression was applied to interpolate them. A number of analyses were carried out including daily rainfall, 2-day/3-day moving values, antecedent precipitation index (API) of 5/10/30xa0days, 10-min intensity, and hourly amounts, and the trigger factor of the debris flow in the study area was also investigated. It was determined that for the triggering of debris flows, both high API values as well as high-intensity short-duration rainfall is needed. It was documented that in cases of solely high API indices or high-intensity short-duration rainfalls, no debris flows were initiated.

Challenges for landslide hazard and risk management in ‘low-risk’ regions, Czech Republic—landslide occurrences and related costs (IPL project no. 197)

The presented work was performed within the scope of the IPL project no. 197, entitled ‘Low frequency, highly damaging potential landslide events in ‘low-risk’ regions – challenges for hazard and risk management’. The Czech Republic is an example of a landslide ‘low-risk’ country with all the related challenges for long-term and sustainable landslide risk management. We argue that the main challenge is to raise and maintain a corresponding level of public attention to landslide hazards and risks. Since hazard and risk recognition by the potentially affected people is the main precondition of any effective risk mitigation, we performed several tasks to provide as yet unavailable information about specific aspects of the occurrence of landslides in the Czech Republic which may attract the attention of the public, including the responsible authorities, to the landslide risk. These aspects include new ways of updating a landslide inventory and compilation of a database of the cost of landslide mitigation works paid by the government. Landslide inventories derived from web sources, the unified system of traffic information of the national road authority and information collected by the Czech Geological Survey were compared. The landslide inventory compiled by the Czech Geological Survey is the most complete, but in some cases, the other two inventories could be used to complete it with landslide events not yet registered. Landslide-related expenses of the state budget are not negligible and their uneven spatial distribution cannot be explained by landslide occurrences only, which calls for in-depth risk assessment.

Snow avalanche hazard of the Krkonoše National Park, Czech Republic

ABSTRACT This paper presents a snow avalanche hazard map of the most avalanche-prone mountain range in the Czech Republic, the Krkonoše Mountains. The map was prepared using historical records of 1132 avalanches which occurred over the last 54 years and state-of-the-art modelling of avalanche propagation and the spatial distribution of potential avalanche source areas. The map provides not only reliable and easy to understand information for the Mountain Rescue Service of the Czech Republic and mountain tourists, but also for land use managers to identify areas where new avalanche paths may develop under favourable conditions, including the total removal of forest cover.

Database of giant landslides on volcanic islands—first results from the Atlantic Ocean

Giant landslides on volcanic islands represent the largest formations which can be created in a single geological moment. Such landslides are distributed across the globe and have attracted a significant amount of research interest. Yet, no coherent attempts have been made to rationalise this information into a single online resource. This report summarises information about the structure of the recently created database of giant landslides on volcanic islands and presents some observations regarding the uncertainties inherent in the inventories. The database is being prepared over a 3-year period: the first year of the project has focused on rationalising information about giant landslides around the Atlantic Ocean while the second and third years will focus on rationalising information about such landslides from the Pacific Ocean and Indian Ocean, respectively. Using this database, it should be possible to interrogate the spatial and temporal patterns of land sliding and landslide reactivation as well as to better assess the hazard and potential risks posed by giant landslides on volcanic islands. It will be particularly interesting to see if any evidence can be found for global triggers, such as eustatic or climatic changes, instead of the more commonly expounded local triggers. Ultimately, it is hoped that the database will benefit both the geoscientific community and those agencies responsible for civil defence. This work is part of the activities of the International Consortium on Landslides, namely its International Programme on Landslides (Project n. 212). The database is available from the giant landslides project webpage: https://www.irsm.cas.cz/ext/giantlandslides.

Large landslide stress states calculated during extreme climatic and tectonic events on El Hierro, Canary Islands

Composed volcanic edifices are particularly prone to large-scale failures—these often result from the acceleration of preexisting deep-seated gravitational slope deformations. Consequently, a complete understanding of the kinematic behaviour of such slope deformations would represent an important step towards mitigating against human casualties or fatalities and damage to critical infrastructure. In this manuscript, a 9-month time series of three-dimensional fault displacement measurements has been used to determine the stress states of the San Andrés Landslide on El Hierro in the Canary Islands. These stress states have been calculated on the basis of single-displacement events using a novel approach which only requires information about the magnitude of the movement vector and its orientation. The analysis focused on four specific periods: a reference period in November 2013; an extreme rainfall event at the beginning of December 2013; and two endogenous impulses at the end of December 2013 and during the middle of March 2014. On the basis that the direction of principal stress represents a marker for the direction of landslide mass movement, it has been possible to define six landslide activity modes which correspond to specific stress states. The response of the landslide to the extreme rainfall event was immediate and reflected increasing saturation of the porous landslide mass. The response of the landslide to the endogenous impulses was more complicated as compressional pulses often alternated with gravitational relaxation. In this study, it is demonstrated that the landslide stress state can be determined on the basis of a single-displacement event whenever fault displacements are monitored in three dimensions. This innovative approach may represent a valuable step towards a complete understanding of the kinematic behaviour of potentially catastrophic slope deformations, particularly those which are in a critical stability state.

Studies on selected landslides and their societal impacts: activity report of the Prague World Centre of Excellence, Czech Republic

Research and dissemination activities of the World Centre of Excellence on Landslide Risk Reduction (WCoE), located in Prague, Czech Republic, entitled “Landslide risk assessment and development guidelines for effective risk reduction” focus on the strengthening of landslide risk reduction efforts defined through the Sendai partnership and the International Program on Landslides (IPL). WCoE’s contribution to this objective is represented mainly by long-term landslide monitoring, site-specific, and regional hazard assessment as well as a variety of dissemination activities targeting the general public and those involved in landslide risk management. Apart from the Czech Republic and Slovakia, research was performed in the regions where landslides may have considerable negative impacts on society (e.g., South America, Africa) or where landslide processes may be significantly enhanced by climate change (arctic regions and high, glaciated mountains).