Large scale volcanic events are extremely rare. The earth has not seen a VEI-8 sized eruption (an eruption that deposits more than 1,000 cubic kilometers of volcanic material) since Taupo’s Oruanai eruption over 25,000 years ago. Additionally, there are only a few known VEI-8 sized eruptions that have occurred during the past 1 million years.
It’s important to understand however, that geological time scales work on a much slower schedule than human time scales. While these events are still rare (even on a slow geological time scale) they are not unusual, and have occurred regularly throughout the history of our planet, and will continue to do so long after we’re gone.
Types of Large-Scale Volcanism
Flood Basalt Events
Flood basalt events are likely the largest volcanic events that we have seen on a regular basis through earth’s history. Unlike more well-known volcanic events (such as super-eruptions), flood basalt eruptions tend to be more effusive, and rarely have a large explosive component to them. As you would expect from an event so large, they are extremely rare, with the last flood basalt event being the Columbia River Basalts, which occurred over 15 million years ago in the states of Washington, Oregon, and Idaho.
While flood basalt events may not have the explosive signatures we normally would associate with destruction, their sheer size and scale can make them the most potent volcanic type of event that we know about, with many being implicated as potential causes of planetary extinction events.
How big are flood basalt events?
To give a sense of perspective, the Columbia River Basalts was a comparatively small flood basalt event, and it covered over 210,000 square kilometers of land in the states of Washington and Oregon.
The Siberian Traps Flood Basalt Event, is estimated to range from 1-4 million cubic kilometers of magma, and the region covered would be large enough to cover all of western Europe in a magma layer over 1000 meters high (1).
Suffice it to say, flood basalts (also known as trap events) are ridiculously large, on a scale that is difficult to fathom. The one caveat to this is that there is a much longer timescale for flood basalt events than you would see for a one-shot VEI-8 sized eruption. Most flood basalt events occur during a period of time that can last as long as a million years, so it may not be entirely accurate to characterize flood basalt events as singular events.
VEI-8 Explosive Eruptions
VEI-8 explosive eruptions are often referred to as “supervolcanic” eruptions. While the word “supervolcano” a particularly scientific word, it does describe the sheer scale of these explosions. Aside from large asteroid or comet impacts, VEI-8 eruptions are likely the most singularly destructive events that occur on our planet.
Most people first think of Yellowstone volcano when the term “supervolcano” comes to mind, but there are quite a few active volcanoes on Earth that have erupted on a VEI-8 scale aside from Yellowstone. Also, the earth will see new VEI-8 volcanoes emerge in the geological future, since they are a regular phenomenon.
Large Igneous Provinces
A Large igneous province is simply a term that refers to a large region on earth that is covered by volcanic products.
Technically speaking, flood basalt events are a variety of large igneous provinces, and many VEI-8 supervolcanoes sit within a region that would be defined as a large igneous province (although this would often refer to a collection of independent volcanoes that occur in that region instead of the singular supervolcano).
Basaltic Large Igneous Provinces
Basaltic large igneous provinces include most flood basalt formations on land as well as the ocean floor, and also include many large basaltic provinces that are similar in size to flood basalt events, but occur at a significantly slower rate. Currently, the island and country of Iceland would qualify as a basaltic large igneous province.
Silicic Large Igneous Provinces
Silicic large igneous provinces are extremely rare and poorly understood. Unlike basaltic large igneous provinces, Silicic large igneous provinces are extremely violent by nature. They seem to occur when there is a flareup of extremely intense explosive volcanism. An example of a currently active silicic large igneous province would be the Taupo Volcanic Zone in New Zealand.