**1. Introduction**

Catastrophic geomorphic processes in river valleys of volcanic regions (as well as in nonvolcanic ones) may result from various natural events, such as floods due to high-intensity rains, fast snow melting, or a water breakthrough from lake dammed by landslide or rockfall bodies. The areas of the present-day volcanicity are distinct for yet another catastrophe catalyst in river valleys: endogenic factor, primarily volcanic eruptions. The latter are often responsible for the descent of volcanic mudflows—lahars—related to melting of glaciers, snow caps on the volcanic

#### **Figure 1.**

*Location of the volcanoes, mountains, and other objects described in this paper (yellow circles; numbering corresponds to the mentioned order in the text): 1 - Nevado del Ruiz volcano (vlc.), Columbia; 2 - Avachinsky vlc., Kamchatka, Russia; 3 - Mendeleev vlc., Kunashir Isl., Russia; 4 - Merapi vlc., Indonesia; 5 - Chaiten vlc., Chile; 6 - Vesuvius vlc., Italy; 7 - Spurr vlc., Alaska, USA; 8 - Bezymyanny vlc., Kamchatka, Russia; 9 - Eastern Sayan Mountains (Mnts.), East Siberia, Russia; 10 - Khamar-Daban Mnts., East Siberia, Russia; 11 - Pampas Onduladas lava flow, Mendoza, Argentina; 12 - Ksudach caldera, Kamchatka, Russia; 13 - Shiveluch vlc., Kamchatka, Russia; 14 - St. Helens vlc., Washington, USA; 15 - Grimsvötn vlc., Iceland; 16 - Katla vlc., Iceland; 17 - Akademia Nauk caldera, Kamchatka, Russia; 18 - Ruapehu vlc., New Zealand; 19 – Numazawa vlc., Japan; 20 - Kuril Lake caldera, Kamchatka, Russia; 21 - Mutnovsky vlc., Kamchatka, Russia; 22 - Agua vlc., Guatemala; 23 - Kelud vlc., Indonesia; 24 – Laachen see vlc., Germany; 25 - Uson-Geysernaya caldera, Kamchatka, Russia; 26 - Anyuyskiy vlc., Chukotka, Russia; 27 - Undara lava flow, Queensland, Australia; 28 - Hawaiian islands, USA; 29 - east African rift zone (Nyiragongo vlc., Congo); 30 - Sikhote-Alin' Mnts., Far East, Russia; 31 - East Manchurian Mnts., Far East, Russia; 32 - Klyuchevskoy vlc., Kamchatka, Russia; 33 - Cotopaxi vlc., Ecuador; 34 - Fuego vlc., Guatemala; 35 - Taupo volcanic zone, New Zealand; 36 - Sarychev peak vlc., Matua Isl., Russia; 37 - Tolbachik vlc., Kamchatka, Russia; 38 - Parinacota vlc., Chile; 39 - Shasta vlc., California, USA; 40 - Casita vlc., Nicaragua.*

cones, or abundant rainfalls. Among them, there is a notorious lahar developed at the Nevado del Ruiz volcano eruption in Columbia (**Figure 1**) in 1985 and killing 23,000 people [1].

As summarized by Ref. [2], more than 200 million people are living in settlements within 200 km distance from active or potentially active volcanoes, that is, within the zones of immediate danger. Most of the towns and settlements within that zone are either confined to river valleys or located in close vicinity to them. As seen from the statistics cited by the specialist, 17% of human deaths during the eruptions result from lahars that occur typically in the river valleys, and another 27% from the pyroclastic flow, the maximum thickness of the latter being usually confined to topographic lows. So, the maps of endangered areas show as a rule river valleys and adjoining territories as the most hazardous, even in case they are at a considerable distance from volcanoes, see maps of volcanic regions Avachinsky [3] and Mendeleev [4] volcanoes (Kuril-Kamchatka region of Russia - See **Figure 1**), Merapi (Indonesia) [5], and many others (**Figure 2**). A good example is Chaiten town (Chile) partially destroyed because of the descent of the lahars along the Blanca River valley in

*Catastrophic Processes in River Valleys of Volcanic Regions: Geomorphologist's Point of View DOI: http://dx.doi.org/10.5772/intechopen.108141*

#### **Figure 2.**

*Schematic map of volcanoes impact zones: 1 - river valleys originating on the volcano: Lahars, floods, and pyroclastic flow dominate; 2 - volcano foot: Pyroclastic flows, hot avalanches and lahars, lava flows, and toxic gas emissions dominate; 3 - volcano slopes: Frequent impact of pyroclastic and lava flows, rockfalls, toxic gas emissions, and formation of extrusive domes; 4 - settlements; 5 - agricultural land; and 6 - forests.*

#### **Figure 3.**

*The Chaiten town (Chile) was demolished by lahars in 2008–2009 after Chaiten volcano eruption (see Figure 1, No 5). Buildings on the Blanco river banks: A - left bank, b - right bank. White arrow—Lahar deposits (2010, here and thereafter all photos are courtesy of the author unless stated otherwise).*

2008–2009 during the Chaiten volcano eruption. The areas of the town directly adjacent to the river suffered the most (**Figure 3**). Areas closer to the volcano but further from the river were only partially covered with ash.

The sequence of catastrophic events—"eruption-volcanic mudflow (lahar) descent" is well studied and quite common [2, 6–12], etc. To take one example, A. Neri and his colleagues [13] considered 12 scenarios of potential eruptions of Vesuvius volcano different in type and the subsequent development of catastrophic processes on its slopes; the specialists arrived at the conclusion on the probable lahar descent in eight cases. There is a commonly accepted distinction made between primary (or hot) mudflows immediately following the eruption and secondary (cold) ones that may occur a few decades after it. It should be noted that mudflows could form even on the slopes of extinct volcanoes under favorable conditions (steep slopes, loose material abundance, etc.).

When viewed more closely, the catastrophic processes in river valleys of volcanic regions display a considerable diversity of factors accountable for mudflow formation; besides, the spectrum of hazards is notably wide. Quite frequently, an endogenic event—an eruption—entails not a single catastrophic (endo- or exogenic) process, but a series of interrelated and sequentially developing catastrophes, that is, a cascade of hazardous processes.

Good examples are described in Ref. [14], where lahars associated with 1953 and 1992 eruptions of the Spurr volcanic complex descending along Crater Peak Creek (Chakachatna River tributary, Alaska, USA—— see **Figure 1**) blocked the main river with the formation of dammed lakes of quite impressive volumes (from 3.2 to 12 x 107 m3 ). The destruction of temporary dams and the descent of lakes led to debris flows. The author concludes that the formation and failure of debris dams is a common process in this river valley and a consequence of pyroclastic eruptions of the Spurr volcanic complex.

This work is aimed at the analysis of the causes and subsequence of the hazardous phenomena in river valleys of the volcanic regions with different types of volcanic and post-volcanic activity. The methodology used is based on a thorough analysis of high and ultra-high-resolution satellite images followed by field geomorphological observations, including the study of the relief and geological structure of the territory, loose sediments, and bedrock. In key areas, a morphometric analysis of the longitudinal and transverse profiles of the valleys was carried out, and deposits of lahars and mudflows, dammed lakes, fragments of destroyed dams, and their genesis were studied. An important stage was the critical analysis of literary sources. The identification of connections and interdependencies of geological phenomena and chains of catastrophic geomorphological processes under conditions of the dominance of various types of volcanism—effusive, explosive, volcano-tectonic phenomena, and gas-hydrothermal processes—made it possible to create a classification scheme of catastrophic processes in volcanic regions river valleys. In the process of creating the scheme, the types of predominant volcanism, the nature of the volcanic material and the types of its movement, concomitant factors, and the sequence of catastrophes were identified. The cases studied by the author during her geomorphologic field survey in the volcanic regions of Russia and abroad as well as the literature analysis made it possible to identify up to two tens probable scenarios—successions of catastrophic events in river valleys (**Table 1**). In every case, the type of endogenic factor and specific features of its manifestation were taken into consideration, along with specific environmental characteristics (geology and geomorphology, hydrology, climate, and glaciation). The results may be important for the purpose of forecasting dangerous event, and for protecting people against endogenic natural disasters.


*Catastrophic Processes in River Valleys of Volcanic Regions: Geomorphologist's Point of View DOI: http://dx.doi.org/10.5772/intechopen.108141*



*Catastrophic Processes in River Valleys of Volcanic Regions: Geomorphologist's Point of View DOI: http://dx.doi.org/10.5772/intechopen.108141*

*Catastrophic processes in river valleys of volcanic regions.*

**Table 1.**
