On May 18, 1980 – 40 years ago – many people in the Lower Mainland and Vancouver Island awoke to a boom from the south. Mt. St. Helens had been stirring for quite some time. Geologists had predicted an eruption.
At 8:32:11 a.m., the volcano finally let go. Its weakened north face slid away from the caldera creating the largest landslide on record in North America. The partly molten rock beneath was finally freed. Gases erupted from the mountain spewing ash over a vast area covering 11 states, along with B.C. and Alberta. Pyroclastic flows of super-heated rock and ash rushed down through the valleys and over the hills of the surrounding region clogging rivers and decimating forests. A total of 57 people and thousands of animals lost their lives.
Volcanoes are part of our history. From Vesuvius to Krakatoa to Mt. Pelee to Mt. St. Helens, we have been witness to the power within the Earth. Volcanoes have also been key in our understanding of the processes fueling the Earth.
British Columbia and New Zealand both sit on the “ring of fire” – the path of volcanoes surrounding the Pacific Ocean plate. Volcanoes are not always located on plate boundaries – witness the Hawaiian Islands which have been created over a molten hot spot in the middle of the Pacific Ocean plate. However, the ring of fire clearly delineates the boundaries of the Pacific.
British Columbia does not presently have any active volcanoes but there are numerous cones predominantly clustered in four fields – Garibaldi just north of Vancouver, Wells Gray-Clearwater in the Caribou, the Anahim giving rise to Rainbow Ridge and the Stikine extending from Prince Rupert to the Yukon. The coastal zones are contiguous with the Cascade Volcanic Arc, which includes Mt. St. Helens and is part of the ring of fire.
New Zealand has many active cones. On Dec. 9 last year, White Island/Whakaari erupted resulting in 21 fatalities among the 47 on the island at the time. The island is just the tip of a stratovolcano.
Stratovolcanoes are shaped in the way we typically think of volcanoes. They are steep-sided and conical in structure with layers of lava and ash. The lava is thin enough to flow down the side but thick enough so that it doesn’t flow far.
Other common types of volcanoes include shield volcanoes which are much flatter (the Rainbow Range is a peralkaline shield volcano) as they are formed predominantly from a thinner form of lava and dome volcanoes (such as Garibaldi) form from a much thicker acidic lava which cannot flow far leading to a dome-like structure.
British Columbia is also home to rare tuya volcanoes, which form under glaciers. During the last glaciation event covering the province, eruptions resulted in the formation of sub-surface lakes which eroded the top of the volcano leading to table-like structures.
The study of volcanoes or volcanology has benefitted from the development of analytical chemical and physical techniques over the past 40 years. In the past, the only warning of an eruption might be ground tremors or steam from a volcanoes peak but often these signs were missed and the surrounding countryside was decimated by a sudden eruption.
However, by analyzing gases being emitted from various vents, scientists are now able to have a better understanding of what is going on down below. Infrared spectroscopy is useful for determining the chemical composition of simple gas mixtures. Excess carbon dioxide and carbon monoxide stick out like a sour thumb in the instrument.
Gas chromatographs are capable of breaking down more complex gas mixtures and sorting out all of the compounds present. They work on the basis of retention rates for the gases as they pass through a porous substrate in a column. By carefully choosing the type of column, the concentrations of a whole range of gases can be identified.
Similarly, mass spectrometers – particularly when coupled with a gas chromatograph – can provide a detailed picture of the components present in an emissions from a volcano.
Modern GPS systems can be refined to detect both vertical and horizontal ground movements of only a few millimeters. Combined with satellite imagery, it is possible to see changes in the ground surrounding a volcano that often indicate the movement of molten lava. The volcanic eruption of Anak Krakatau in 2018, which resulted in half the island sliding into the sea, was heralded by very subtle movements detected in hindsight. But refinements in the technology may turn the tables and allow the technology to predict future eruptions.
Scientists are even learning to listen to volcanoes as moving magma is often accompanied by ultra-low frequency sound waves.
Modern volcanology is a very active discipline. It is by no means perfect but as we understand more and more about the forces involved, it is hoped we will be able to predict eruptions before they happen.
