INTRODUCTION AND STUDY AIMS

 

Landslides around the world are a relevant natural process but it is difficult to quantify the global distribution because of the variable reliability of reporting and documentation of landslides in different nations. Also, landslides are an important hazard in the world and the economic cost and the human lives loss are difficult to quantify due to landslides should be combined with other hazards (e.g., earthquakes, floods) (Sidle, 2006).

 

Landslides are an important element in the landscape of the Canary Islands. Valleys, cliffs and land use couldn’t be explained without this process. Thus, landslides are the fundamental key to understanding the landscape in the islands (Villalba, 1996), especially in the occidental islands such as Tenerife and El Hierro which are the focus of this study.

 

The origin of the landslides in The Canary islands is mainly volcanic activity (Carracedo et al., 2008) and this point is fundamental to understand the landslide process in the different islands and the evolution across the islands.

 

Studying the landslides areas could give important information about the characteristics and effects of them in the post-landslide processes. Human location, physical elements and the distribution of the vegetation is affected by the landslide processes, and it is a relevant geomorphological process in the landscape of the island (Villalba, 1996).

 

The Canary Islands have a high frequency of landslides. In the last 1 ma the higher frequency of landslides has occurred due islands having a high altitude and being unable to support the weight of all materials. Recent landslide processes are the most evident, and fourteen landslides have affected the islands in the last 1 ma while only ten landslides have been registered in rest of that timeline. Nonetheless, according to Cendrero (1996), the frequency of destructive landslides is low but they represent an important hazard when pyroclastic eruptions are very long, because earthquakes and high eruptions processes increase the risk.

 

A relationship between the age of the islands and the frequency of the landslides could be deduced as we can observe in the figure 3. The main reason is the altitude of the islands that is bigger in the islands with more landslides, and also the erosive processes are relevant in this relationship.

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3. Relationship between age of the landslides and islands. (Data source from Alonso et al., 2005; Masson, et al. 2002; Anguita et al., 1999 and Seisdedos et al., 2012 and basemap from GRAFCAN).

 

 

Moreover, there exists in the Canary Islands a relationship between the concentration of the affected areas for the landslides, age of the islands and islands with three fracturing axes as is evident in the figure 4. Islands with more affected area have three fracturing axes and the volcanic activity is more recent while, islands with less concentration have less volcanic activity and less altitude due to the erosive processes in the landscape.

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4. Comparison of % landslide areas affected in the different islands. (Source: GRAFCAN).

 

This dissertation is based mainly in Tenerife because this island is subject to the highest number of landslides due to the three fracturing axes. A comparison with El Hierro will be important because it is the most recent island, and characteristics are very similar, but in the initial stages of the island formation.

 

Accordingly, the aims of this study are to:

 

1. Analyse the impacts of the landslides in the landscape

2. Study the characteristics (slope, hydrology and land use) and effects on the landslides

3. Determinate if the landslides are the main factor in the geomorphology on the landscape in Tenerife.

 

The objectives of this study are located the landslides across the islands, describe and perform an analysis of their characteristics as the slope or hydrographic network. In based to the results of this analysis, actual land use will be evaluated in the landslides areas of Tenerife and El Hierro, and if there are different circumstances between both islands. Additionally, the evaluation between a landslide area and an area without landslide will be useful because the possible differences between the physical variables and the land occupation could be an important result to understand the landscape of the island. Guimar town area will be used because this town has a part in landslide area and other part outside the area affected for the landslides.

 

The objectives of this research are thus to:

 

1. Locate the landslides and the affected area.

2. Analyse the physical characteristics: Slope and hydrological network

3. Influence of physical characteristics in the land use

4. Differences between areas with landslides and areas without landslides

5. Analyse landslides as main factor in the distribution of the societies

 

Therefore, this research is focuses on the role of the landsliding in Tenerife and assesses whether it is the main influencing in the land occupation around the island. Analyse the characteristics and determinate the landslide areas are essential to understanding the geomorphology processes in the islands, and how the physical elements have been modified by the landslides.