## 2 Materials and Methods
### Materials
#### 2.2.2 Field Data  
Dry rarely is the process of the rolling, bouncing, and sliding of loose material down a slope, which is the dominant transformational process along the cliffs of the west parts of Lefkada Island [50]. A sediment trap was used for the first time on Lefkada Island to collect sediment flux through dry ravel (Figure 4). The installation site is located on Egremni cliff, within the tectonically active zone of the CTF. The climate in this specific region is semiarid Mediterranean, and its lithology consists of moderate to weakly consolidated Pliocene-Pleistocene fanglomerate, resulting in a soil-mantled hillslope. The sediment trap was constructed from a roof gutter, which was one meter long and 0.25 m in height.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Year** & **Data** & **Source** & **Number of Photos** & **Spatial Resolution** & **Type** \\ \hline
2000 & IKONOS bundle & USGS & 1 & 1.00 m & Digital \\  & imagery & & 20 & 1.00 m & Analogue \\
2004 & Airphotos & & 1 & 0.50 m & Digital \\
2008 & Orthomosaic & & & 5.00 m & Digital \\
2008 & DSM & & & 5.00 m & Digital \\
2015 & Pleiades bundle & 1 & 0.50 m & Digital \\
2016 & Pleiades stereo pair & 1 & 0.50 m & Digital \\
2003 & Landsat-5 & Multiple & 30.00 m & Digital \\
2004 & Landsat-5 & Multiple & 30.00 m & Digital \\
2015 & Landsat-8 & Multiple & 30.00 m & Digital \\
2016 & Landsat-8 & Multiple & 30.00 m & Digital \\ \hline \hline \end{tabular}
\end{table}
Table 1: Remote sensing data used in the current research.  
Removable covers were placed at the ends of the trap in order to collect sediment as well as to clean the trap. To collect sediments, we used a brush and a plastic bag that was mounted at one of the ends of the gutter. This selected type of trap imitates a similar experiment by [PERSON] [51] since most of the sediment flux in the area is coarse grained. The installation of the trap was performed three years after the 2015 earthquake that mobilized a wide sliding zone [20]. The total duration of this experiment was almost two years, ranging from November 2018 to October 2020, when the last sample was collected. Afterwards, the trap was destroyed for an unknown reason.  
It is worth mentioning that dry ravels are complicated phenomena that involve mixtures of sediments with wide grain size distributions. In light of this, we assumed that we would lose the finer fractions of the granular phase, e.g., clay and silt, as they mix with water, due to the fact that our sediment trap was not able to collect water. The coarser grain clast of angular cobble captured in the sediment trap was at the maximum diameter of 135 mm (Figure 5). The possible grain size of the larger cobbles or even boulders not captured in the trap are rare [20]. Therefore, we considered the sediment in the trap as representative of the dry ravel process in the area. Larger boulders can be detected and mapped using high resolution imagery acquired with UAVs [20,21]. Concerning the rest  
Figure 4: The sediment trap that was placed on the overhanging cliff located in Egremni beach.  
of the sample, we applied dry sieving with a mechanical shaker. The used sieves were wire-meshed and stacked, with mesh sizes spaced primarily at 1 \(\phi\) intervals. The samples were dried for 24 h and they were weighed before sieving. The mass and the respective collection periods of each of the samples are presented in Table 2. Six sieves with the following diameters: 8 mm, 5.6 mm, 4 mm, 2 mm, 0.50 mm, and 0.25 mm were used to separate the collected material into different classes, i.e., gravels (8 mm) to fine sand (0.25 mm).