The Effects of Volcanic Eruptions Observed in Satellite Images: Examples from Outside the North Pacific Region
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CHAPTER 11 The effects of volcanic eruptions observed in satellite images: Examples from outside the North Pacific region Robert Wright, Andrew J.L. Harris, Ronnie Torres, Luke P. Flynn 11.1 CHAPTER SYNOPSIS ing these effects. Using a range of case studies for three contrasting volcanoes and eruption styles, we The effect of a volcanic eruption by liberating then illustrate how the regional and global effects of magma, gases, and energy is to modify the Earth’s volcanic eruptions have been documented using surface and its atmosphere. Quite how these satellite images. changes are produced depends on the nature of the eruption; for example, whether it is explosive or effusive, the period of time over which the erup- tion occurs, the mass of material erupted, and the geographic area over which the erupted products 11.2 INTRODUCTION: OBSERVING are distributed. The eruption of lava flows, the em- THE EFFECTS OF VOLCANIC placement of pyroclastic flows and lahars, and the ERUPTIONS USING deposition of volcanic ash all serve to change the SATELLITE IMAGES landscape surrounding the volcano. The injection of ash and gas into the Earth’s atmosphere not only The effect of a volcanic eruption, by transferring alters its composition but, through this under cer- magma and gas from beneath the Earth’s crust to tain conditions, has the ability to influence Earth’s a position above it, is to modify the Earth’s surface climate. These effects can be more than climatic and its atmosphere in a variety of ways and over a or geomorphic. Indeed, the often close proximity range of spatial and temporal scales. The exact between humans and erupting volcanoes means nature of the effect of an eruption depends on the that these agents of change also constitute a hazard. type of volcano, the chemistry of the magma Many of the preceding chapters in this book erupted, the period of time over which the eruption have been concerned with describing how satellite occurs, and the geography of the area over which data can be used to provide quantitative data the erupted products are distributed. The eruption regarding the nature of various eruptive products of lava flows, the emplacement of pyroclastic flows and processes. The purpose of this chapter is to and lahars, and the deposition of volcanic ash can illustrate how insights into the many effects of vol- all serve to alter the geomorphological, hydro- canic eruptions, at both the regional and global logical, and ecological characteristics of the land- scales, can be gleaned from remotely sensed data scape surrounding the volcano, while the injection sets. To this end, we begin by summarizing the ways of ash and gas into Earth’s atmosphere not only in which volcanic eruptions can affect their sur- modifies its composition but can also, as a conse- rounding environment and the attributes that make quence, influence regional weather and global satellite remote sensing a suitable method for study- climate. © Springer-Verlag Berlin Heidelberg 2015 323 K.G. Dean and J. Dehn (eds.), Monitoring Volcanoes in the North Pacific, Springer Praxis Books, DOI 10.1007/978-3-540-68750-4_11 [email protected] 324 The effects of volcanic eruptions observed in satellite images Significantly, the close proximity between alter the pre-eruption landscape, but this time over humans and erupting volcanoes means that, in a relatively small geographic area and over a period addition to simply impacting Earth’s surface and of a decade (Figure 11.2). Although the eastern half atmosphere, the products of an eruption may also of the island is obscured by clouds in the 1989 pre- constitute a hazard. Blong (1984) identifies 13 vol- eruption image the impact of pyroclastic flows, canic hazards, defined as those products of an erup- lahars, and ash fall on the southern half of the tion that impact upon people, their possessions, island is obvious. their lifestyles, and their environments, a list which However, the effects of an explosive eruption includes lava flows, ballistic projectiles, tephra fall, need not be as complex, and the processes that pyroclastic flows, debris avalanches, lahars, jo¨ kulh- combined to produce the changes observed at Mt. laups, seismic activity, ground deformation, tsu- St. Helens and Soufrie` re Hills Volcano can also act nami, atmospheric effects, acid rain, and acid in relative isolation. The April 18, 1993 eruption of gases. The effects of these hazards are many and Lascar Volcano, Chile, resulted in the emplacement varied and include the impact that eruptions have of pyroclastic flows that extended 7.5 km from the on humans both directly, as a result of physical and summit crater complex (Denniss et al., 1996). The psychological trauma, and indirectly, through their emplacement of these flows, which are clearly impact on infrastructure, agriculture, commerce, visible in Figure 11.3, was the major consequence and even tourism. of this eruption. Tephra fall is an obvious effect of Some of the effects of volcanic eruptions, such explosive eruptions, although identification of the as the destruction of houses by lava flows, can be deposits in satellite images can prove difficult, detected and chronicled using satellite images; unless the volumes involved are large or images others, such as the psychological trauma inflicted are acquired quickly, as ash is quickly reworked on those evacuated from the houses, obviously by wind and rain. However, ash fall on snow and cannot. This chapter is not intended to provide a ice is particularly easy to identify. Mt. Belinda, only detailed commentary of all the possible effects, recently identified as an active volcano (Patrick et physical and socio-economic, presented by volcanic al., 2005), lies in the South Sandwich Islands, an hazards; for this we refer the reader to Blong (1984). isolated archipelago in the South Atlantic Ocean Rather, the purpose of this chapter is to illustrate (Figure 11.4). In this high spatial resolution how insights into many of the products of volcanic ASTER image dark localized ash deposits, possibly eruptions, and some of their effects, can be gleaned produced during a recent strombolian explosion from remotely sensed images. from the summit vent, can clearly be seen on the The emplacement of lava flows, lahars, pyro- eastern side of the volcano’s summit. clastic flows, and ash has a clear effect on the land- Volcanic sector collapses are relatively rare, scape surrounding a volcano: they re-surface it, and it would be misleading to say that their effects often over short periods of time and sometimes over have been routinely observed during the era of considerable areas. The effects of an explosive erup- satellite remote sensing, due to the limited oppor- tion are perhaps the most dramatic illustration of tunity for before-and-after image pairs. Satellite this. On May 18, 1980, Mt. St. Helens erupted images did, however, play a key role in demonstrat- approximately 0.2 km3 of magma in 9 h, devastat- ing that large sector collapses were more common ing 600 km2 of the surrounding area (Christiansen than had at first been thought (Francis and Wells, and Peterson, 1981). Pyroclastic flows, ash fall, 1988), and images such as the one depicted in lahars, a directed blast and debris avalanche acted Figure 11.5, which shows the landslide deposit in concert to produce the changes depicted in Fig- produced by a collapse that occurred at Socompa ure 11.1, which included the destruction of mature Volcano in Chile (see Wadge et al., 1995) make it stands of coniferous forest and substantial changes easy to visualize just how potent a geomorphic to the local lacustrine and fluvial system. The erup- agent such an event can be. tion cost U.S.$2.7 billion and the lives of 57 people One of the most infamous volcanic disasters of (Fisher et al., 1997). At Mt. St. Helens these recent years, the eruption of Nevado del Ruiz, changes occurred over a large area, with the Colombia in 1985, was caused by the rapid em- majority (those associated with the initial directed placement of lahars (volcanic mudflows) in blast), concentrated within several hours. At Sou- response to the melting of the volcano’s summit frie` re Hills Volcano, Montserrat, many of the same glacier during an eruption. More than 23,000 volcanic processes have combined to significantly people, mainly in the village of Armero, were killed [email protected] Introduction: observing the effects of volcanic eruptions using satellite images 325 Figure 11.1. (Top) Landsat Multi-Spectral Scanner (MSS) standard false-color composite image of Mt. St. Helens, acquired on July 29, 1972. MSS bands 7 (0.8–1.1 mm), 5 (0.6–0.7 mm), and 4 (0.5–0.6 mm) are displayed in red, green, and blue, respectively. (Bottom) Landsat Thematic Mapper (TM) image of Mt. St. Helens, acquired on August 26, 1986. TM bands 4 (0.76–0.9 mm), 3 (0.63–0.69 mm), and 2 (0.52–0.60 mm) are displayed in red, green, and blue, respectively. MSS data have a nominal pixel size of 79 Â 79 m; TM pixels are 30 m on a side. In both images, healthy vegetation appears red, bare soil cyan, and ash gray. The pre-eruption Mt. St. Helens is snow- capped. The post-eruption image was acquired more than 6 years after the main May 18, 1980 eruption, but the effects of the eruption on the landscape are still obvious. Obvious changes have occurred with respect to the geomorphology of the volcano itself, the summit of which has been replaced with a 400 m diameter crater. Spirit Lake, the southern bank of which was directly impacted by the debris avalanche, can be seen immediately north of the volcano.