Pre-1991 Eruption:
* Composite Cone: Mount Pinatubo was a classic stratovolcano, built up over time by layers of lava flows, ash, and volcanic debris.
* Caldera: Before the 1991 eruption, Pinatubo had a small, shallow caldera at its summit.
* Fumaroles: Numerous fumaroles (vents releasing volcanic gases) were present on the volcano, indicating its active nature.
Post-1991 Eruption:
* Large Caldera: The 1991 eruption dramatically changed the volcano's shape, creating a large caldera approximately 2.5 kilometers (1.6 miles) wide and 800 meters (2,600 feet) deep.
* Pyroclastic Flows: The eruption generated massive pyroclastic flows, fast-moving currents of hot gas and volcanic debris that devastated the surrounding area.
* Ash Fall: The eruption ejected a vast amount of ash into the atmosphere, which fell over a wide area, causing significant environmental damage.
* Lahars: Following the eruption, heavy rainfall triggered massive lahars (volcanic mudflows), which caused widespread destruction and loss of life.
* Volcanic Domes: After the main eruption, several volcanic domes formed inside the caldera, indicating continued volcanic activity.
Other Notable Features:
* Hydrothermal System: Mount Pinatubo has a significant hydrothermal system, which contributes to the formation of hot springs and other geothermal features.
* Lava Flows: While not as prominent as other features, lava flows have played a role in the volcano's development.
Mount Pinatubo's dramatic 1991 eruption not only changed the landscape of the Philippines but also served as a reminder of the immense power of volcanic forces. The volcano continues to be monitored closely for signs of future activity.
