The Lazio region of central Italy has many landforms of volcanic origin, including several large lakes that mark the locations of ancient volcanoes. This photograph from an astronaut on the International Space Station highlights two such lakes—Lago di Vico and Lago Bracciano—located to the northwest of Rome.
Both lakes are located within calderas, large depressions that form after violent, explosive eruptions empty a volcano’s underlying magma chamber. Any remnants of the volcanic edifice can then collapse into the newly-formed void, leading to the creation of large depressions. These depressions can fill partially or completely with water, forming permanent lakes.
Lago Bracciano (image right) is approximately 8 kilometers (5 miles) across at its widest point, and is located 32 kilometes (20 miles) northwest of Rome. The volcanic activity at Lago Bracciano began approximately 600,000 years ago and continued to approximately 40,000 years ago as part of the formation of the Sabatini volcanic complex. While part of the lake formation was due to the collapse of part of a large magma chamber, the current caldera also was formed by movement along numerous faults in the area—a process known as volcano-tectonic collapse.
Located approximately 24 kilometers (15 miles) to the north-northwest of Lago Bracciano, Lago di Vico occupies part of a caldera associated with eruptive activity that began about 800,000 years ago and continued until 90,000 years ago. The caldera was formed largely by the catastrophic eruption of the Vico volcano approximately 200,000 to 150,000 years ago. The final phase of volcanic activity in the caldera led to the formation of a small lava cone in the northeast quadrant known as Mount Venus.
The extent of the lakes of Bracciano and Vico are readily apparent in this image due to sunglint—light reflecting back from the water surfaces towards the observer. This reflection gives a mirror-like sheen to the water surfaces. Dark green forested areas associated with parks are visible near both lakes, while light gray to white regions indicate human settlement, such as the city of Viterbo and tilled fields.