# Assessment of Internal and External Factors Causing Slow-Moving Landslides
## 3 Results and Discussion
### Analysis of Stratigraphy, Topography, and the Scale of Occurrence
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Sn.** & **Ga.** & **Sg.** & **Cr.** & **Ir.** & **J.** & **Js.** & **Ss.** & **Wd.** & **Sod.** & **St.** & **A.** & **Sld.** & **Sa.** \\ \hline
1 & Unk & Okc & Mr & Ne & 2 & 6–20 & Ne & Wr & 60–90 & SL & 162.5 & 21.2 & N50W \\
2 & Car & Pye & Sr & Ne & 2 & 6–20 & E & Sr & 30–60 & SL & 225.3 & 23.9 & N32W \\
3 & Cre & Gye & Ir & Ne & \(\geq\)3 & 6–20 & E & Wr & <30 & SiCL & 161.3 & 25.1 & N30W \\
4 & Cre & Bul & Ir & Ne & \(\geq\)3 & 6–20 & E & Nr & 30–60 & SiL & 122.5 & 30.0 & N35W \\
5 & Cre & Gye & Sr & Ne & 2 & 6–20 & Ne & Wr & 30–60 & L & 68.8 & 22.6 & N30W \\
6 & Cre & Gye & Sr & E & 2 & 6–20 & E & Wr & <30 & L & 60.0 & 23.8 & N23E \\
7 & Ter & Yon & Sr & Ne & 2 & 20–60 & E & Wr & 30–60 & L & 117.5 & 22.9 & N25W \\
8 & Per & Pye & Sr & Ne & \(\geq\)3 & 6–20 & Ne & Wr & <30 & SL & 587.5 & 35.0 & N50W \\
9 & Pre & Sob & Mr & Ne & \(\geq\)3 & 6–20 & Ne & Wr & <30 & SL & 41.3 & 32.7 & N29W \\
10 & Pre & Sob & Mr & Ne & \(\geq\)3 & 6–20 & Ne & Wr & <30 & SL & 33.8 & 29.5 & N28E \\
11 & Pre & Yul & Mr & E & 2 & 20–60 & Ne & Wr & 30–60 & SL & 41.3 & 18.3 & N20W \\
12 & Unk & Unk & Ir & Ne & 2 & 20–60 & Ne & Wr & 30–60 & L & 41.3 & 23.4 & N35W \\
13 & Pre & Seo & Mr & Ne & 2 & 6–20 & Ne & Wr & 30–60 & L & 27.5 & 16.7 & N30W \\
14 & Unk & Okc & Mr & Ne & \(\geq\)3 & 6–20 & Ne & Wr & 30–60 & SL & 111.3 & 17.6 & N30W \\
15 & Cre & Gye & Sr & Ne & \(\geq\)3 & 6–20 & Ne & Wr & <30 & LS & 131.3 & 17.3 & N25E \\ \hline  & & & & & & & & & & & & & & \\ \hline \hline \end{tabular} Note: Sn. = Site No., = geographical age, Sp. = supergroup or group, Cr. = composition rock, Ir. = intrusive rock, J. = joint (No.), Js. = joint spacing (mm), Sn. = stony slope, Wd. = weathering degree, Sob. = soil depth (cm), St. = soil texture, A. = altitude (m), Sld. = slope degree (”), Sa. = slope aspect, Unk = unknown, Car = Carboniferous, Cre = Cretaceous, Ter = Tertiary, Per = Permian, Pre = Precambrian, Okc = Okchon group, Pye = Pyeongan group, Gye = Gyeongsang supergroup, Bul = Bubbles grazing, Yon = Yomi group, Sob = Sobaeggan gneiss complex, Yul = Yuli group, Seo = Season group, Mr = metamorphic rock, Sr = sedimentary rock, Ir = igneous rock, Ne = nonexistence, E = existence, Wr = weathered rock, Sr = soft rock, Nr = normal rock, SL = sandy loam, SiCL = silty clay loam, SiCL = silty clay loam, SiCL = silt loam, L = loam, and LS = loamy sand.  
\end{table} 
Table 4: Stratigraphy, topography, and the scale of slow-moving landslide areas. The average altitude of the slow-moving landslide areas was 128.9 m (27.5-587.5 m), corresponding to hill areas, which is consistent with the finding that slow-moving landslides mainly occurred in hill areas [11,15]. However, one slow-moving landslide area occurred at an altitude of 587.5 m, which was a unique case in which the slow-moving landslide phenomenon affected the summit of the mountain due to the cutting of the lower part under the quarrying project. The average slope of slow-moving landslides in South Korea is 24\({}^{\circ}\), ranging from 16.7\({}^{\circ}\) to 35\({}^{\circ}\). Approximately 51% of Korean mountainous regions have steep slopes of 20\({}^{\circ}\) or more [35]. The slope direction of the slow-moving landslide area was northwest in 12 sites (80.0%) and northeast in 3 sites (20.0%) (Table 4). The direction of the slow-moving landslides corresponded with the slope direction in all 15 sites. The slow-moving landslide was analyzed as occurring in the direction of the flow of materials comprising the slope of the mountainous area based on the slope degree. The analysis of the scale of slow-moving landslides revealed that their average range was 191.9 m (84.2-446.9 m), the average length was 203.2 m (108.2-467.2 m), and the average depth was 2.5 m (1.2-5.8 m) (see Table 5). These scales were smaller than those reported in an analysis of 100 nationally representative slow-moving landslide areas in Japan (200-270 m wide, 300-360 m long, and 18.3-18.6 m deep) [9].