Here's why:

* Stratovolcanoes are characterized by their steep, conical shape, formed by alternating layers of lava flows and pyroclastic material (ash, rocks, etc.).

* Deception Island has a distinct cone shape, even though its caldera has been filled by the sea, and has erupted both lava and pyroclastic materials over time.

While Deception Island is known for its unique caldera, which is essentially a collapsed crater flooded by the sea, this doesn't change its classification as a stratovolcano.