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Fig. 3. Geological map (a) and engineering geological map (b) of the study area with four cross-sections (1-1’, 2-2’, 3-3’ and 4-4’). investigate possible failure modes of rock masses which contain discontinuities (Hussain et al., 2015).

Figure 3 Geological map (a) and engineering geological map (b) of the study area with four cross-sections (1-1’, 2-2’, 3-3’ and 4-4’). investigate possible failure modes of rock masses which contain discontinuities (Hussain et al., 2015).

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The study area stretches 2.1 km along the Balia Nala and is delineated by 29°22’E-29°21’E latitude and 79°28’N—/9°28'23.2” longitude (towards southwest of Nainital, Fig. 1). The elevation ranges from 1450 m to 1920 m. The right bank of this stream has two populated localities, i.e. (a) locality nearby Government Inter College (GIC) and (b) Saraswati Vihar, both affected by landslides. Fig. 2. Average monthly and annual rainfall during 2007-2013 (Source: Aryabhata Research Institute of Observational Science, Nainital).
The study area stretches 2.1 km along the Balia Nala and is delineated by 29°22’E-29°21’E latitude and 79°28’N—/9°28'23.2” longitude (towards southwest of Nainital, Fig. 1). The elevation ranges from 1450 m to 1920 m. The right bank of this stream has two populated localities, i.e. (a) locality nearby Government Inter College (GIC) and (b) Saraswati Vihar, both affected by landslides. Fig. 2. Average monthly and annual rainfall during 2007-2013 (Source: Aryabhata Research Institute of Observational Science, Nainital).
Fig. 1. Geological and location map of the study area (Valdiya, 1988).
Fig. 1. Geological and location map of the study area (Valdiya, 1988).
Fig. 4. Geological cross-sections (1-1’, 2-2’, 3-3’ and 4-4’) along the marked section lines in Fig. 3.
Fig. 4. Geological cross-sections (1-1’, 2-2’, 3-3’ and 4-4’) along the marked section lines in Fig. 3.
Fig. 5. (a) Four sets of joints in the carbonaceous slate. (b) A dextral strike slip fault along the stream with 10 m offset. (c) Shear sense indicator showing dextral movement. (d) 0.5-).7 m high waterfall along the stream. (e) GIC ground showing 0.5 m subsidence. (f) Toppling failure at the right bank of the stream. (g) Cracks in the houses at the right bank. (h) Tensile cracks presented nearby GIC ground. During mapping, many structural features have been documented. Predominant rock type presented in the area is slate of Manora member (greenish color), Kailakhan member (grey to dark grey color) and Nainital lake fault has been described to develop during 40-50 ka (Singhvi et al., 1994) with a movement rate of 6 cm per year (Kotliya et al., 2009). This study indicates that the Nainital lake fault is a result of neotectonic activities in this area. Most prominent evidence is the rapid down cutting along the course of Balia Nala. At locations 7 and 10 (Fig. 3a), two subsidiary faults of the Nainital lake fault are identified along which ~10 m lithological offset (Fig. 5b) of dextral sense has occurred (Fig. 5c). Waterfalls of 0.5-).7 m in height (Fig. 5d) are also characteristic features presented along these faults.
Fig. 5. (a) Four sets of joints in the carbonaceous slate. (b) A dextral strike slip fault along the stream with 10 m offset. (c) Shear sense indicator showing dextral movement. (d) 0.5-).7 m high waterfall along the stream. (e) GIC ground showing 0.5 m subsidence. (f) Toppling failure at the right bank of the stream. (g) Cracks in the houses at the right bank. (h) Tensile cracks presented nearby GIC ground. During mapping, many structural features have been documented. Predominant rock type presented in the area is slate of Manora member (greenish color), Kailakhan member (grey to dark grey color) and Nainital lake fault has been described to develop during 40-50 ka (Singhvi et al., 1994) with a movement rate of 6 cm per year (Kotliya et al., 2009). This study indicates that the Nainital lake fault is a result of neotectonic activities in this area. Most prominent evidence is the rapid down cutting along the course of Balia Nala. At locations 7 and 10 (Fig. 3a), two subsidiary faults of the Nainital lake fault are identified along which ~10 m lithological offset (Fig. 5b) of dextral sense has occurred (Fig. 5c). Waterfalls of 0.5-).7 m in height (Fig. 5d) are also characteristic features presented along these faults.
Fig. 6. Stereographic projection for different locations (L-13, L-14, L-16, L-17, L-27 and L-29) with respect to presented discontinuities, slope and river trend dip of joint J1 (64°) is steeper than that of the slope. Argillaceous slate is exposed along the course of the stream and dolomite is exposed at the top of it. The slates along the course of stream are eroded rapidly. Due to these and neotectonic activities in the area (Kotliya et al., 2009), the rocks at the right bank slide downward due to which toppling failure and subsidence (0.5-1.5 m) of ground are common at GIC ground (Fig. Se and f). It is supported by various evidences such as tilting of poles and ground (Fig. Se), cracks in the houses (Fig. 5g) and tensile cracks on the surface with 0.1-0.3 m wide and 2-3.3 m deep (Fig. 5h). Our surface data show that the GIC ground has 5-10 m thick overburden below which there are tensile cracks (Section 2-2’ in Fig. 4). However, ground penetrating radar (GPR) data (Gupta et al., 2015) also confirmed our observation on GIC. At the left bank, Kelakhan slate underlies the Manora slate. Joint J2 presented in these rocks dips 58°~/8° towards valley, which accelerates the slope failure (L-27 in Fig. 6).
Fig. 6. Stereographic projection for different locations (L-13, L-14, L-16, L-17, L-27 and L-29) with respect to presented discontinuities, slope and river trend dip of joint J1 (64°) is steeper than that of the slope. Argillaceous slate is exposed along the course of the stream and dolomite is exposed at the top of it. The slates along the course of stream are eroded rapidly. Due to these and neotectonic activities in the area (Kotliya et al., 2009), the rocks at the right bank slide downward due to which toppling failure and subsidence (0.5-1.5 m) of ground are common at GIC ground (Fig. Se and f). It is supported by various evidences such as tilting of poles and ground (Fig. Se), cracks in the houses (Fig. 5g) and tensile cracks on the surface with 0.1-0.3 m wide and 2-3.3 m deep (Fig. 5h). Our surface data show that the GIC ground has 5-10 m thick overburden below which there are tensile cracks (Section 2-2’ in Fig. 4). However, ground penetrating radar (GPR) data (Gupta et al., 2015) also confirmed our observation on GIC. At the left bank, Kelakhan slate underlies the Manora slate. Joint J2 presented in these rocks dips 58°~/8° towards valley, which accelerates the slope failure (L-27 in Fig. 6).
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