Santa María had no historical record of eruption. Formed roughly 30,000 years ago along the volcanic belt that lines the Pacific coast of Central America, the cone had stood so quietly for so long that scientists considered it extinct. But in January 1902, a series of earthquakes began shaking western Guatemala. The April 18 quake razed Quetzaltenango and San Marcos, killing a thousand people. For six weeks afterward, smaller tremors rattled the volcano's flanks with unsettling frequency. On September 23, a shock was felt as far away as Mexico. In the town of San Felipe, people described sounds coming from the mountain like a waterfall or an enormous boiler. The warnings were unmistakable, but no one had the framework to understand them. Santa María was waking up.

The main eruption lasted no more than twenty hours, but it ranked among the three largest of the entire twentieth century, scoring a six on the Volcanic Explosivity Index. An estimated eight cubic kilometers of magma blasted from a vent on the southwest flank, carving a crater roughly one kilometer across and three hundred meters deep. Pumice rained over an area of 273,000 square kilometers, and volcanic ash drifted as far as San Francisco, California, 4,000 kilometers away. Within 160 kilometers of the volcano, total darkness lasted for 53 hours. Coffee plantations in Xolhuitz, Costa Cuca, Chuva, Progreso, and Tumbador were buried and never restored. Buildings collapsed under the sheer weight of accumulated ash. In the village of Suiza, a structure packed with people seeking shelter gave way, killing eighteen. Between 5,000 and 8,700 people died.

As thousands of people choked under falling ash, President Manuel Estrada Cabrera had other priorities. His government was staging the Fiestas Minervalias, a lavish propaganda festival meant to glorify his regime's dedication to education and progress. Rather than acknowledge the catastrophe unfolding in the western highlands, Cabrera's administration told citizens the eruption had occurred in Mexico. When Quetzaltenango's regional authorities pleaded for help, the central government replied that no funds were available; the April earthquake had already absorbed the disaster budget. Aid did not reach affected areas until December, nearly two months after the eruption. Quetzaltenango's officials were left to manage on their own, allocating 15,000 pesos for ash removal and another 5,000 to repair shattered aqueducts.

The destruction extended far beyond the eruption itself. Ash smothered the region's agricultural harvest, and regional authorities warned of imminent famine. Cattle died in large numbers, creating a meat shortage on top of the crop failures. The central government permitted Quetzaltenango to import flour tax-free for a few months, a meager concession given the scale of the crisis. Water and power supplies failed, taking months to restore. Meanwhile, gangs moved into devastated areas, stealing from survivors, looting abandoned plantations, and committing murder. On November 12, President Cabrera finally established the General Supply of Aid for Agriculture to support struggling farmers, but by then the damage to communities and livelihoods had compounded far beyond what the eruption alone had caused.

Twenty years of dormancy followed the 1902 disaster before a new phase of activity began in 1922. A lava dome complex called Santiaguito grew inside the crater left by the eruption and remains active today, with more than one cubic kilometer of lava erupted so far. Santiaguito's four domes, El Caliente, La Mitad, El Monje, and El Brujo, have made Santa María one of the most closely watched volcanoes on Earth. The 1902 crater left the southern flank dangerously oversteepened, and scientists monitor the risk that a large earthquake could trigger a massive landslide covering up to 100 square kilometers. Today, Santa María is designated a Decade Volcano, a distinction reserved for peaks that pose the greatest threat to nearby populations and demand sustained scientific attention.