One of the favored topics of a lot of science media is some of the largest of all volcanic activity on Earth — flood basalt provinces (see below). These provinces are vast swaths of land that cover up to hundreds of thousands of square kilometers with tens to hundreds of meters of basalt — the most famous examples are places like the Columbia River Basalts or the Siberian Traps. When these provinces formed, they potentially played a dramatic role in regional and global climate — however, what they aren’t are a single volcanic event. I saw a headline today from Discovery News that called the Siberian Traps “The Deadliest Volcano Ever“. This is a fundamentally flawed idea — flood basalt provinces are made of thousands of fissures and vents that erupted over a wide area for upwards of millions of years. To call any of these flood basalt provinces a single event is like saying the Last Glacial Maximum (Ice Age) was a big snowstorm or the Pacific Ocean is a single dixie cup of water.
Let’s take a look at some of these flood basalts and their extent. The one in the Discovery News article was the Siberian Traps. This flood basalt province (also known as a large igneous province) covers 34o,000 square kilometers (see below) and erupted an estimated 2,000,000 cubic kilometers of basalt lava (for perspective, that is ~111 Mauna Loas, the largest active shield volcano on Earth). The Siberian Traps are ~250 million years old and parts of the province likely formed over 2 million years of activity. However, there are some younger ages that suggest that the activity in the Siberian Traps lasted into the Triassic, spanning 7-8 million years. So, we have a flood basalt province that was at least half the size of Alaska that erupted from 2-8 million years — and it is written about as a single volcano? If anything, the Siberian Traps were like other basaltic volcanic fields on steroids — places like Craters of the Moon or the rift zones of Kilauea, where individual cinder cones, fissures eruptions and shields formed. However, we’re talking about fissures that could be thousands of miles apart, so like these basaltic fields, the Siberian Traps might have shared a similar ultimate source of magma (a rising mantle plume), they are likely as different as volcanoes along a full volcanic arc like the Cascades. Would we ever call the Cascades a “single volcano”?
The Columbia River Basalts are another prime example of a flood basalt province. This province started forming ~16 million years ago and covered a significant portion of Oregon, Washington and Idaho with tens of meters of basalt. This province was smaller than the Siberian Traps, erupting “only” ~170,000 cubic kilometers of basalt lava (only 9.3 Mauna Loas), but this activity spanned 11 million years (with a peak of activity for the first 2 million years). Again, widely dispersed fissures that were active for millions of years — clearly not a single volcano.
My plea is this: stop calling a flood basalt province a singular eruption, singular volcano or singular volcanic event. They aren’t. They represent a large volume of volcanic material, but they encompass activity that was spread over huge regions and long timescales. Their cumulative effect of climate seems to be clear — heightened activity like this for millions of years could add a large burden of volcanic aerosols like CO2, SO2, H2S into the atmosphere. They might even be directly responsible for many of the Earth’s global extinctions. However, they are not like an asteroid impact that happens in an instant. Instead, they are a long process of volcanism over a wide area — and should be treated as such. This is one of the trickiest aspects of thinking like a geologist — thinking in geologic timescales. Not all “events” represent a point in time, but rather related features/processes that occur over long periods (thousands to millions of years). Keeping that idea in mind when you write about geological events will help give the proper context for talking about their ramifications.