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2,500 miles southwest of Los Angeles, Hawaii is a tropical archipelago with summer and winter coastal air averages of 85° and 78° and water averages of 81° and 76°. According to TripAdvisor, “For many, the word vacation conjures images of sunbathing on a sunny beach, paddling in a dazzling blue ocean, napping under coconut trees—in other words, Hawaii”. Certainly, my family trips to its islands of Oahu and Maui during the 70s-80s were experiences into a paradise of sights, sounds and aromas.
After his four-month visit as a Sacramento Union reporter in 1866, Mark Twain praised Hawaii as “the loveliest fleet of islands anchored in any ocean”. History also records his reaction when reaching the summit of the Kīlauea volcano on the Big Island: “The surprise of finding a good hotel in such an outlandish spot startled me considerably more than the volcano did”. Such was the prevailing state of knowledge about the Earth’s crust that he could not know that Hawaii is unanchored, geologically speaking! He was also unaware, indeed as no one was then aware, that the nearby Mauna Kea volcano is the world’s tallest mountain. By rising to 13,800 feet above the Pacific and extending down 19,700 feet to the ocean floor, Mauna Kea is higher than Mount Everest by a mile!
Founded in 1835 and the world’s oldest such institution, the British Geological Survey estimates that the world has more than 1,500 active volcanoes with an eruption frequency varying from almost continuous to dormant with gaps for as long as many hundreds of years. Geological understanding of the Earth’s crustal plates since the 1960s tells us that volcanoes are features of convergent plate boundaries, divergent plate boundaries, and more rarely of hot spots within plates. The first group are along continental margins like the Pacific rim of the Americas and offshore plate margins like north of New Zealand. The second group are along oceanic spreading ridges like Iceland. And examples of the third group underlie Yellowstone, the world’s first national park, and the Hawaiian Islands. In all such situations, volcanoes―which in human historical terms classify as active, dormant or inactive―are fed from an unstable plumbing system of pipes and reservoirs of molten or mushy rock. Accompanied by earthquakes due to ground level changes, eruptions result from peak pressure and temperature phases in the seldom predictable cycle of activity that characterizes the unique history of each volcano.
Almost two thousand years ago, adventurous Polynesians from the Samoan, Marquesas and Tahiti islands began visiting what would not become the US State of Hawaii until 1959. Recent radiocarbon dating points to permanent settlement between 1219 and 1266. As inter-island expeditions progressed, those first Hawaiians evidently recognized the different relative ages of the volcanoes, and their volatility was conveyed in Hawaii’s mythology. The archipelago remained isolated from the rest of the world until, evidently, the Spanish Ruy López de Villalobos spotted them in 1542 and the British James Cook landed there in 1778. Archaeological discoveries have also revealed that early settlers developed an aquaculture in estuaries and streams long before Captain Cook’s arrival and that they likely interacted with people in South America before the Europeans arrived there.
The first geological study of the Hawaiian archipelago was undertaken in 1880–1881 and Hawaii’s volcano observatory was founded in 1912. Today, we know from research on the Earth’s oceans and continents that the Hawaiian Islands are collectively sliding to the northwest at almost three inches per year (equal to almost 50 miles per million years) over a crustal hot spot 300-400 miles wide, as much as 1,000 miles deep, and about 80 million years old. The Big Island is a coalition of four volcanoes named Hualalai, Kohala, Mauna Kea, and Mauna Loa. About 20 miles offshore to the southeast is the youngest volcano named Kamaʻehuakanaloa, currently 3,000+ feet below sea level and not likely to become a new island for several tens of thousands of years. Kauai, the oldest of Hawaii’s Islands to the northwest, is no longer over the hot spot and last erupted about five million years ago. By comparison, geoscientists estimate that the Mauna Loa volcano likely emerged above sea level 300,000 years ago.
My blog about Iceland in this series last October mentioned how oceanic volcanoes become inactive seamounts as their underlying plate slides away from providing source material. To the northwest of the Hawaiian archipelago lies the 6,200 mile long Hawaiian–Emperor seamount chain which comprises more than 80 former volcanoes that stretch from the Aleutian Islands near eastern Russia’s Kamchatka Peninsula to Kamaʻehuakanaloa southeast of Hawaii’s Big Island. As the CEO of the Ontario Science Centre in Toronto in the early 1990s, it was an honor to follow Dr. J. Tuzo Wilson, a Canadian geophysicist, who discovered much of the foundation about plate movements. His hot spot theory was that volcanism can persist in one area for a long time. In 2003, fresh investigations revised the theory about the 47-million-year-old bend in the Hawaiian-Emperor chain which is now interpreted to mark a directional shift in the hotspot's motion relative to the plate's motion.
At the end of the last century, the US Geological Survey issued this summary: “More than 270,000 people have been killed directly or indirectly by volcanic activity worldwide during the past 500 years. Nearly all of the deaths have been caused by explosive eruptions of composite volcanoes along the boundaries of the Earth's tectonic plates. The worst recent volcanic disaster was in November 1985, when mudflows triggered by the relatively small eruption of glacier-capped Nevado del Ruiz Volcano, Colombia, buried the town of Armero and killed more than 22,000 people. In contrast, fewer than a hundred people have been killed by eruptions in the recorded history of Hawaii and only one of them in this century”.
Today in the United States, the most well-known eruption―which quickly became one of the world’s most studied volcanoes―was that of Mount St. Helens in the Cascade Range in 1980. On the 40th anniversary of its eruption, the US Forest Service recalled: “57 people lost their lives and hundreds of homes, buildings and structures were destroyed… After the eruption, the summit of Mount St. Helens was gone, forests were obliterated and rivers followed new courses. More than 150 new lakes and ponds were formed, and existing lakes filled with sediment, flooding their banks. The eruption created a mosaic of disturbances where the landscape continues to change”. About 650 miles downwind in Edmonton, Alberta, my house and car were covered with its gritty ash.
The Mediterranean Sea is a zone of plate convergence between Africa and Europe. Italy’s Vesuvius just east of Naples famously erupted in AD 79, catastrophically destroying Pompeii and several other Roman cities. From a detailed eyewitness account of the eruption by Pliny the Younger, it is instructive that he did not mention Pompeii: this incinerated and buried town remained unknown until the late 16th century and its archaeological excavations, today a major tourist site with often 15,000 daily visitors, did not begin until 1748. Vesuvius ranks among the world’s most dangerous volcanoes because more than half a million live in its immediate vicinity and 2-3 million more live close enough to be affected by its sudden and violent eruptions.
Heard as far away as Alaska, the tumultuous eruption of Tonga in the southwest Pacific on January 15, 2022 has been summarized by National Geographic: “… the tremendous energy of this latest explosion, which NASA estimated to be equivalent to five to six million tons of TNT, is unlike any seen in recent decades. The eruption sent a tsunami racing across the Pacific Ocean. It unleashed a sonic boom that zipped around the world twice. It sent a plume of ash and gas shooting into the stratosphere some 19 miles high, with some parts reaching as far as 34 miles up. And perhaps most remarkable, all these effects came from only an hour or so of volcanic fury.” Yet Tonga was less powerful than the peak explosion of Krakatoa between Java and Sumatra on August 27, 1883, reputedly the loudest sound ever heard, which ejected some five cubic miles or rock fragments in the air and ash over some 300,00 square miles, killed 30,000+ people across Indonesia, and triggered higher tsunami waves across the Indian Ocean.
The combination of a trend favoring cultural motivations in leisure travel while the distribution and degree of natural hazards have not lessened obliges us to be attentive to what should be learned from breaking news and from our travel plans. It is only a matter of time before a dormant or ‘inactive’ volcano becomes active: foreseeably, the desire to predict eruptions will continue to be thwarted by the complexity of natural processes. However, the ‘good news’ is that the science of geology has greatly improved our knowledge―but only if we wish to learn it―about the different risks of proximity to the different types of volcanoes. As the above cited examples reveal, destinations along divergent plate boundaries and over oceanic hot spots―because of their lower magnitude of pre-eruption earthquakes and less volatile eruptions―pose an exponentially lower risk to life and infrastructure than destinations along convergent plate boundaries.