Explanation:

Volcanic eruptions can be classified into different types based on their explosiveness and the type of volcanic activity. The four types of eruptions mentioned in the question are Pelean, Hawaiian, Strombolian, and Vulcanian.

Pelean Eruption:
- Pelean eruptions are characterized by the explosive nature of volcanic activity.
- They are named after the 1902 eruption of Mount Pelée in Martinique, which devastated the town of Saint-Pierre.
- Pelean eruptions are caused by highly viscous magma that traps gases and builds up pressure within the volcano.
- The pressure eventually leads to a violent explosion, resulting in the ejection of pyroclastic flows (fast-moving clouds of hot gas, ash, and volcanic materials) that can travel at high speeds and cause significant destruction.

Hawaiian Eruption:
- Hawaiian eruptions are characterized by relatively gentle and non-explosive volcanic activity.
- They are named after the volcanoes in Hawaii, where this type of eruption is commonly observed.
- Hawaiian eruptions occur when basaltic lava (low viscosity magma) reaches the surface and flows out of the volcano in a steady manner.
- The lava typically forms rivers or lakes and can flow for long distances without causing significant damage.

Strombolian Eruption:
- Strombolian eruptions are characterized by mild to moderate explosive volcanic activity.
- They are named after the volcano Stromboli in Italy, which is well-known for its frequent Strombolian eruptions.
- Strombolian eruptions occur when gas bubbles within the magma burst at the surface, ejecting incandescent lava fragments into the air.
- These eruptions are often rhythmic and can create a fountain-like display of lava.

Vulcanian Eruption:
- Vulcanian eruptions are characterized by short but violent explosive volcanic activity.
- They are named after the volcano Vulcano in Italy, where this type of eruption was observed.
- Vulcanian eruptions occur when highly viscous magma becomes trapped within the volcano, leading to a buildup of pressure.
- The pressure eventually causes a powerful explosion, ejecting ash, gases, and volcanic materials into the atmosphere.

Answer:
- Based on the characteristics of the different types of eruptions, the Hawaiian eruption is the one that is not usually explosive.
- Hawaiian eruptions are known for their relatively calm and non-explosive nature, with lava flowing steadily from the volcano.
- The low viscosity of the basaltic lava allows it to flow easily, reducing the buildup of pressure and preventing explosive eruptions.
- Instead of explosive activity, Hawaiian eruptions often create lava flows that can be hazardous but less destructive compared to other types of eruptions.