The Beginning

He [Pliny the Elder] was at Misenum in his capacity as commander of the fleet on the 24^th of August, when between 2 and 3 in the afternoon my mother drew his attention to a cloud of unusual size and appearance. He had had a sunbath, then a cold bath, and was reclining after dinner with his books. He called for his shoes and climbed up to where he could get the best view of the phenomenon. The cloud was rising from a mountain – at such a distance we couldn't tell which, but afterwards learned that it was Vesuvius. I can best describe its shape by likening it to a pine tree. It rose into the sky on a very long ‘trunk’ from which spread some ‘branches’. I imagine it had been raised by a sudden blast, which then weakened, leaving the cloud unsupported so that its own weight caused it to spread sideways. Some of the cloud was white, in other parts there were dark patches of dirt and ash. The sight of it made the scientist in my uncle determined to see it from closer at hand.

From Pliny the Younger’s eyewitness account of the 79 CE (Common Era; substitute for AD, Anno Domini) Vesuvius’s eruption, translated from his Letter 6.16 to the historian Tacitus by Prof. Cynthia Damon (2000), Amherst College, Massachusetts.

Almost two millennium after Pliny the Younger’s insightful description of the Vesuvius eruption that resulted in the death of his uncle and entombed the residents of Pompeii and Herculaneum, modern volcanology is still in its infancy. Like a child with boundless enthusiasm and seemingly endless opportunities, volcano science has yet to develop fully an identity of its own. Instead, it freely draws upon such diverse disciplines as geology, seismology, hydrology, geochemistry, and geophysics. Fewer than half of the scientists who study volcanoes would call themselves volcanologists, and therein lies a great strength. Volcanology is inherently a multidisciplinary pursuit with ample room for specialists and generalists alike – physicists, chemists, biologists, hydrologists, limnologists, dendrochronologists, ecologists, remote-sensing specialists, and many others. Scientists who study volcanoes often find themselves looking beyond their own expertise for answers, surrounded by others doing the same. For novices and experts alike, volcanoes are humbling but very exciting subjects to explore.

In spite of the best efforts of countless volcano watchers dating back at least to Pliny the Younger, no unifying theory yet exists to explain the diversity and complexity of magmatic and volcanic systems. This may be due in part to the tremendous breadth of volcanic phenomena (e.g., bubbling mudpots and lava lakes; steaming hot springs and jetting lava fountains; lavas that flow freely, others seemingly too stiff to move, and others still that explode into towering ash columns and swift pyroclastic flows; geysers that entertain onlookers by erupting on schedule and rare, caldera-forming cataclysms that threaten entire civilizations). To make matters worse, all of this diversity is served up with a heavy dose of complexity. Earth’s deep interior is not only hidden from direct view, but it is also heterogeneous in virtually every way imaginable. Before it explodes or oozes onto the surface, magma forms deep within the Earth, rises through extreme conditions of pressure and temperature, interacts physically and chemically with diverse crustal rocks, cools, partially crystallizes and degases, sometimes mixes with other magmas of similar complexity, responds to regional tectonic influences, and interacts to varying degrees with groundwater. Each of these processes leaves an imprint on the eruptive or intrusive end products, so the complete sequence of events can be exceedingly difficult to decipher.

All of this says nothing about the additional complexity that arises when magma finally reaches the surface, where it interacts with the atmosphere, hydrosphere, and biosphere. During the past two centuries, more people have died as a result of tsunamis, lahars (volcanic mudflows), and post-eruption starvation and disease associated with eruptions than as a direct result of eruptive processes. On the island of Hawai 0 i, many residents’ complaints of unusual respiratory problems have been attributed to ‘vog’ (volcanic fog) or ‘laze’ (lava haze), a product of previously undocumented interactions between seawater and basaltic lava flows as they pour into the Pacific Ocean from a long-lived eruption of Kilauea Volcano (Monastersky, 1995). Atmospheric scientists still debate the relative contributions of anthropogenic and volcanic sources of several gases that play an important role in sustaining life on Earth. Because they reflect our planet’s inherent complexity from mantle to stratosphere, volcanoes present an immense challenge to those who strive to understand them.

Responding to crises that threaten the lives and livelihoods of thousands of people, volcano scientists at the beginning of the 21st century still rely to a great extent on collective experience and intuition to anticipate the outcome of volcanic unrest. In the words of two scientists who played key roles in the mitigation effort surrounding the historic 1991 eruption of Mount Pinatubo, Philippines, ‘Successful mitigation of volcanic risks requires correct forecasts, effective warnings, and a willingness of public officials and citizens to take necessary precautions. Volcanologists should be prepared for obstacles and delays at each step and should be aware that, even when progress is being made toward such forecasts, warnings, and precautionary actions, the margin of safety can be alarmingly narrow.’ (Newhall and Punongbayan, 1996, p. 807). Happily, this situation is improving rapidly. The past 25 years have witnessed several important advances in our understanding of volcanic processes, products, and attendant hazards. Progress has been spurred both by technological improvements and by inexorable encroachment of cities onto the flanks of dangerous volcanoes. Tragically, a major impetus for this change was the highest death toll from a single eruption since the beginning of the 20th century. In 1985, more than 23,000 people died as a result of lahars triggered by an eruption of Nevado del Ruiz Volcano in Colombia – the deadliest eruption since 1902, when pyroclastic flows from Mont Pelée claimed nearly 30,000 lives in the town of St. Pierre on the island of Martinique, West Indies (Fisher et al., 1980; Fisher and Heiken, 1982).

In response, volcanologists focused their efforts on eruption prediction and volcano-hazards mitigation, with encouraging results. Volcano seismology has evolved from a descriptive science based on cataloging events toward a deterministic theory of the mechanisms of several distinctive types of earthquakes that commonly occur beneath volcanoes. Volcano geochemistry has taken its place with seismology and geodesy as a mainstay of modern volcanology, in part by providing some of the earliest and most definitive indicators that fresh magma was involved in several recent episodes of volcanic unrest that culminated in eruptions. Remote-sensing techniques have been applied to volcanoes with increasing frequency and success, promising a future of global volcano surveillance by spaceborne sensors.

The global telecommunications revolution, especially the Internet and World Wide Web, has profoundly changed the way in which scientists monitor volcanoes and share information. Although the presence of trained scientists at volcano crises will continue to be essential for effective hazards mitigation, in most places it is now possible to establish a virtual volcano observatory to share information globally in near-real time. Scientists monitoring a remote volcano can draw upon the expertise of colleagues around the world, even as hazardous events are unfolding. At the same time, advances in volcano geodesy have brought powerful new tools to bear on problems of volcano monitoring and hazards assessment. At the start of a new millennium, volcanology seems to be passing from infancy to adolescence, anxious to establish a unique identity among its more mature siblings in the Earth sciences.

This blog focuses on one aspect of volcanology’s recent advances that I have been fortunate to experience firsthand – a revolution in volcano geodesy. During my career, not one but two breakthrough techniques for measuring surface deformation from space have burst on the scene: the Global Positioning System (GPS) and interferometric synthetic aperture radar (InSAR). Earth scientists have coined the phrase ‘space geodesy’ and put the concept to good use studying geodynamic processes, including volcanism. Other technological advances have made it possible to measure crustal strain in situ with amazing precision over a very wide range in frequency, blurring the distinction between seismology and geodesy. Although traditional techniques are still the best choice for many tasks, a growing collection of new tools has greatly extended the reach and capability of classical geodesy.

In one sense, volcano geodesy is a very specialized field with relatively few practitioners. On the other hand, the subject is sufficiently intuitive to have widespread appeal among many non-specialists who are fascinated by volcanoes and curious about how they work. This blog is by no means a comprehensive treatment of modern geodetic techniques applied to volcanoes, nor is it a historical account of the development of volcano geodesy. For a more systematic treatment of geodetic principles and practices, the reader might want to consult a reference book on geodesy or surveying such as Bomford (1980), Davis et al. (1981), or Krumm et al. (2002). For an overview of geodetic techniques applied to volcanoes, the article on ground deformation methods and results by Van der Laat (1996) is a good choice. Readers interested in a more general treatment of volcanology or volcano hazards might want to consult excellent texts on those subjects by Williams and McBirney (1979), Latter (1989), Francis (1993), Scarpa and Tilling (1996), Fisher et al. (1997), or Decker and Decker (1998).