Volcanic Eruption vs. Earthquake: What Comes First?

When discussing the sequence of events leading to a volcanic eruption, a common question arises: which occurs first, an earthquake or a volcanic eruption? This article delves into the intricate relationship between seismic activity and volcanic activity, providing insights for monitoring volcanic regions and understanding the forces at play.

Understanding the Begins and Means of Volcanic Activity

At any volcano, whether existing or newly formed like those in Iceland, earthquakes typically precede any volcanic eruption

It's important to note that while I am not an expert or a geologist, this article draws from various sources and my personal experiences, such as witnessing the 1980 eruption of Mount Saint Helens.

Mount Saint Helens and the Connection Between Earthquakes and Eruptions

Near the 18th of May 1980, geologists at the US Geological Survey (USGS) in Washington observed a deep earthquake within the mountain on the morning of the eruptive event. This earthquake triggered the north face of the mountain, which had been bulging outward, to slide down, releasing gases trapped within the mountain and causing the eruption to blast out horizontally, a phenomenon distinguishing it from typical volcanic eruptions which usually erupt vertically out of the ground. This event, tragically, resulted in the deaths of 57 people.

Mechanisms of Volcanic Activity and Seismicity

Small earthquakes or tremors near a volcano can be an ominous indication that a volcano may erupt; however, such tremors can also result from magma movements below the caldera. The interaction between volcanism and plate tectonics is complex, and it's challenging to predict the exact sequence of events due to the variability and lack of direct observation under the surface. Sometimes, seismic activity and volcanic activity can occur simultaneously or in reverse.

Measurement and Prediction of Volcanic Activity

Local earthquakes that occur before, during, and after a volcano's eruption can provide valuable data for predicting the behavior of a specific volcano. Scientists and monitoring services use such earthquakes to gauge potential hazards and guide evacuation plans, should an eruption be imminent.

The Case of Kilauea Volcano in Hawaii

Volcanoes like Kilauea in Hawaii, which erupted with lava flows, exhibit more predictable patterns post-eruption, allowing experts to forecast where lava might flow next. In contrast, ash-explosive volcanoes, like Mount St. Helens, display less predictable and more dangerous behavior. Minor earthquakes beforehand often signify an impending eruption but do not always occur. These ash-explosive volcanoes release significant pressure in a vast and sudden eruption, diverging from the gradual movement seen in Kilauea alike volcanoes.

Earthquakes Along Fault Lines

Massive, earth-shaking earthquakes along fault lines or near areas where two plates meet can be challenging to predict, occurring over a long period with sporadic, large quakes. These earthquakes are indicative of the ongoing stress and movement within the Earth's crust, making it essential to monitor seismic activity for potential hazards.