Chapter 1: The Boring Volcanic Landscape

As you approach Portland, Oregon, from the east, you pass through the quaint town of Boring, surrounded by a series of gently rounded hills. At first glance, this landscape may appear to be the result of natural erosion over eons, but in reality, it is sculpted by a unique geological feature: numerous small volcanoes. The Boring Volcanic Field, which the US Geological Survey recognizes as an active volcanic zone, includes notable formations such as Mount Tabor and Mount Scott, both integrated into the urban fabric of Portland.

These diminutive volcanic structures, classified as cinder cones and vents, exist under the towering shadow of Mount Hood, which rises more than 11,000 feet as one of the most prominent peaks in the Cascade range. In contrast to the grandeur of Mount Hood, which has erupted multiple times over the past 500,000 to 700,000 years, the Boring volcanoes are monogenetic, meaning they erupt only once, reach heights between 600 and 1,000 feet, and then become dormant. Collectively, the Boring Volcanic Field comprises over 80 distinct vents and cones.

Section 1.1: The Historical Eruptions of Boring

The Boring volcanoes are primarily situated within the Portland Basin and boast a rich volcanic history marked by several eruption episodes. The earliest eruptions trace back to 2.6 to 2.4 million years ago, occurring roughly 20 miles south of modern-day Portland. After a significant pause of nearly a million years, volcanic activity resumed around 1.6 million years ago, expanding to cover the entire current area of the volcanic field.

The most recent addition to this field is Beacon Rock, a cinder cone that formed just 57,000 years ago along the banks of the Columbia River. Initially, the structure featured a classic conical shape, surrounded by tephra. However, the Missoula floods, which surged through the Columbia River Gorge 15,000 years ago, dramatically altered its appearance by eroding the surrounding material and leaving behind an 848-foot tall cylindrical formation that now serves as a striking landmark for visitors entering the Columbia River Gorge Scenic Area.

Subsection 1.1.1: The Geophysical Forces at Play

The origins of the Boring Volcanic Field can be traced to the Cascadia subduction zone, where the Juan de Fuca oceanic plate is being pushed beneath the North American plate. As this slab descends towards the mantle, it generates heat and pressure that form magma reservoirs. This magma periodically breaks through to the surface, giving rise to the small volcanoes that characterize this region. However, Portland is not the only area with such volcanic fields.

Chapter 2: The Potential for New Eruptions

Recent discussions in a Newsweek article suggest that new volcanic activity could emerge at any moment in the American Southwest. This claim focuses on monogenetic volcanoes, similar to those found in the Boring Volcanic Field, with roughly 2,200 of these formations identified in the southwestern United States and the nearby Mexican state of Sonora.

Over the last 2.6 million years, these volcanoes have formed at an average rate of one eruption every 1,170 years, with some occurring as recently as 1,000 years ago. However, volcanic activity is not consistent; it tends to manifest in bursts, interspersed with lengthy periods of dormancy. Cities like Flagstaff, Arizona, and Albuquerque, New Mexico, are situated within known volcanic fields, where the last eruption in Flagstaff was approximately 1,000 years ago. Geologist Greg Valentine, a co-author of the paper “Quaternary basaltic volcanic fields of the American Southwest,” estimates an 8 percent chance of an eruption in the next century.

While the idea of eruptions happening “anywhere at any time” is intriguing, it must be balanced with a couple of important points. First, eruptions are limited to active volcanic fields, and the Southwest is not a singular extensive volcanic area. Secondly, an average of one eruption per millennium does not present a significant risk for most people.

Next time you find yourself admiring the majestic Mount Hood, Mount Rainier, or any other towering volcano in the American West, don't forget about their smaller volcanic counterparts that continue to emerge across the region.