Summary
Highlights
In 1942, farmer Dionisio Pulido witnessed the sudden emergence of Paricutin volcano from his cornfield. Over 9 years, its lava and ash covered more than 200 square kilometers, highlighting the unpredictable nature of volcanic eruptions stemming from magma's origins.
Volcanoes begin with magma, formed when ocean water penetrates the Earth's mantle, lowering its melting point. This magma is usually held beneath the surface by a delicate balance of three factors: lithostatic pressure (the weight of the crust), magmastatic pressure (magma pushing back), and the rock strength of the Earth's crust.
A common cause of eruptions is increased magmastatic pressure. Dissolved compounds like water or sulfur in magma form high-pressure gas bubbles. These bubbles, similar to CO2 in a shaken soda, lower magma density and increase buoyant force, leading to explosive eruptions as they burst upon reaching the surface. This process likely caused the Paricutin eruption.
Buoyant bubbles form either when new gassy magma rises from deeper underground or when existing magma cools. As magma hardens, minerals solidify, concentrating dissolved gases into explosive bubbles.
Eruptions can also occur from decreased lithostatic pressure, known as 'unloading.' This can be caused by landslides, which rapidly remove rock from above a magma chamber, or by long-term processes like erosion or melting glaciers. The 1980 Mount St. Helens eruption was triggered by unloading, and concerns exist that climate change-induced glacial melt could increase volcanic activity.
The third trigger for eruptions is a weakened rock layer. Acidic gases and heat from magma cause hydrothermal alteration, turning rock into soft clay. Tectonic activity, such as earthquakes creating fissures or stretching the crust, can also weaken the rock, allowing magma to escape.
Despite understanding eruption causes, predicting them remains difficult due to the challenges in measuring changes in magmastatic pressure. However, volcanologists are using new technologies like thermal imaging for subterranean hotspots, spectrometers for analyzing escaping gases, and lasers to track changes in a volcano's shape, aiming to better understand and predict these explosive events.