Phenomena similar to tsunami in Russian internal basins

3. Tsunamis of Landslide Origin

Figure 4

[12] Many tsunamis in lakes and rivers are caused by landslides: underwater and above-water ones. In particular, this is the nature of tsunami in Nizhniy Novgorod that occurred in 1597 on the Volga River. It is described in detail in [Didenkulova, 2006; Didenkulova and Pelinovsky, 2002; Didenkulova et al., 2003]. On 18 June 1597, an enormous landslide destroyed completely the Pechera monastery located at a distance of a few kilometers from the Kremlin of Nizhniy Novgorod down the Volga River. Part of the coastal cliff carried away the houses of the monastery and protruded into the Volga over a distance of more than 100 m, which caused "terrible waves" on the river. The anchored vessels down the monastery were thrown ashore over almost 50 m [Gatsisky, 2001]. This monastery is shown in Figure 4. The author also [Gatsisky, 2001] informs that partial displacements of the slope were observed at least a week before the described event. Many springs opened after the landslide. It is possible to conclude that an increase in the groundwater level and thinning of the ground caused the landslide.

Figure 5

[13] After the landslide, it was decided to build a new monastery at a distance of 3500 ft upstream the Volga. Even in the new place, the history repeatedly reports about sliding down of monastery walls although not so strong as in 1597. For example, in May 1829, during the spring flooding, cracks began to show up behind the houses of the monastery village at a distance up to 400 m along the shore, and the land together with gardens descended. The gardens, which displaced down the slope over a distance of almost 15 m, stopped without damage [Gatsisky, 2001]. At present, the monastery is at the risk of destruction again, which is evidenced by a crack in its wall from the Volga River side (Figure 5).

Figure 6

[14] It is noteworthy that the Volga slope is very steep, which facilitates the landslides. It is written in the same chronicle that in 1867 a large landslide occurred over the so-called salt-storage. The landslide hazard is high even at present. For example, according to the data of the Environment Protection Committee of Nizhniy Novgorod region (they are presented in our paper cited above), only in 2000, in Nizhniy Novgorod at the locations of landslide slopes of the Oka and Volga rivers three new landslides were formed and 33 old ones activated. In 2000, the maximal landslide activity was recorded. The largest among the newly formed landslides was the one in Pochinsky ravine (within the city). Its length is 45 m, width is 30 m, the depth of displaced rocks is 5 m. The main causes of the occurrence of landslides are precipitation, high level of ground waters, and erosion of the coast. On 9 November 2004, the last significant landslide occurred in Bogorodsky region near Nizhniy Novgorod. A ground volume of approximately 10 thousand cubic meters collapsed from a high shore of the Oka River from a height of approximately 50 m (Yu. Smirnova, 2004). We organized investigation of this event (Figure 6) to check whether it induced a tsunami. However, it was found that the landslide stopped not reaching the water level. However, this event evidences one more time the necessity of estimating the tsunami generated by landslides.

[15] It is worth noting that landslide phenomena are also characteristic of other regions of the Volga River. For example, a landslide is described in [Tatevosyan and Mokrushina, 2003], which occurred in 1839 in Fedorovka village near Syzran (approximately 450 km from Nizhniy Novgorod). During this event, notable unrest and oscillations of land were observed, which lasted three days, later they decayed gradually. This landslide could possibly be accompanied by the generation of waves in the river, and we include this event in the summary as a possible tsunami. We also note landslide events at the shore of Sura River in Poreyskoye village of Simbirsk region in 1865 and in Saratov in 1884 [Tatevosyan and Mokrushina, 2003].

[16] A description of tsunami in 1885 on Irtysh River is given in book [Levin and Nosov, 2005]. The wave generated as a result of landslide turned over and threw to the opposite coast a vessel that passed at a distance of one kilometer from the place of the collapse.

[17] Among tsunami waves observed in artificial water supply reservoirs the most impressive example is the formation of a wave 235 m high in Vajont (Italy) reservoir on 9 October 1963, which occurred as a result of collapsing of cliff rocks with a volume up to 270 mln. cubic meters near the dam [Panizzo et al., 2005]. This event was already mentioned in the Introduction. The giant wave propagated to the valley of Piave River covering Longerone town, which resulted in the death of all its inhabitants. The event of 1963 was the second in the history of the reservoir. On 4 November 1960, during the first filling of the basin, a landslide occurred (with a volume of 700,000 m³ ) that caused a 10-meter tsunami wave at the coast. In the other Italian water supply reservoir (Pontesei), a 20-meter tsunami wave generated on 22 March 1959 by a landslide killed a bicyclist that moved along the road [Panizzo et al., 2005]. Formation of big waves in Russian water supply reservoirs is also recorded (Krasnoyarsk reservoir in 1970); however, specific data were not given [Mamradze et al., 1991], thus we relate this case to possible tsunamis.

[18] It is clear from the facts described above that landslide phenomena are frequently accompanied with wave generation and calculation of tsunami waves should be part of estimating the landslide phenomena in rivers, lakes, and water reservoirs.