Preserved for its caves and volcanic features since 1925, Lava Beds serves as an outdoor school for professional and amateur geologists alike. Although it covers only ten percent of the surface area of the massive Medicine Lake shield volcano, the largest in the Cascades Range, it contains excellent examples of the many formations volcanic eruptions can leave behind. Dozens of lava tube caves, the top of a cinder cone, a hollow spatter cone, and wide expanses of jagged lava fields show features that formed rapidly during eruptive periods as lava exploded into the air or flowed downhill for miles. Though the volcano is a half-million years old, its most recent eruption at Glass Mountain occurred only 900 years ago, suggesting that lava may someday erupt here again, erasing old features and recreating the landscape once more.