Different volcanic eruption types show very different levels of explosiveness. Which one of the following types of volcanic eruptions is generally not highly explosive and is usually gentle and effusive?

Introduction / Context:
Volcanoes erupt in different styles depending on the magma composition, gas content, and tectonic setting. Some eruptions are violent and explosive, while others are relatively gentle and produce flowing lava. This question focuses on identifying the eruption type that is usually not explosive and is instead characterised by quiet, effusive lava outpourings, which is a standard topic in physical geography and geology.

Given Data / Assumptions:

• The question asks which eruption type is not usually explosive.
• Options include Pelean, Hawaiian, Strombolian, and Vulcanian eruptions.
• We assume familiarity with the basic classification of volcanic eruptions.

Concept / Approach:
Hawaiian eruptions are associated with very fluid basaltic lava and relatively low gas content. The lava flows out quietly through fissures or from vents, creating shield volcanoes with gentle slopes, such as those in Hawaii. In contrast, Pelean, Strombolian, and Vulcanian eruptions are all more explosive. Pelean eruptions involve pyroclastic flows, Strombolian eruptions include discrete explosive bursts, and Vulcanian eruptions are short but violent explosions. Therefore, the eruption style that is generally not highly explosive is Hawaiian.

Step-by-Step Solution:
Step 1: Recall that Hawaiian eruptions are typical of shield volcanoes like Mauna Loa and Kilauea in Hawaii, where lava fountains and flows are common but large explosions are rare. Step 2: Recognise that this style involves low viscosity basaltic lava that can flow easily, reducing pressure build up. Step 3: Compare with Pelean eruptions, which are named after Mount Pelee and involve dangerous pyroclastic density currents. Step 4: Remember that Strombolian eruptions, named after Stromboli volcano, have regular small explosions that eject incandescent lava clots. Step 5: Note that Vulcanian eruptions are characterised by short, violent eruptions that can blast out ash and rock fragments. Step 6: Therefore, among the given types, Hawaiian eruptions are the ones that are not usually highly explosive.

Verification / Alternative check:
Geology references often present a scale of eruptive styles from least to most explosive, usually starting with Hawaiian at the gentle end and moving up through Strombolian, Vulcanian, Pelean, and Plinian. Hawaiian eruptions are described using words like effusive and quiet, while the others are labelled as explosive. This ranking confirms that Hawaiian is the correct answer for an eruption type that is not usually explosive.

Why Other Options Are Wrong:

• Pelean eruption: Known for powerful pyroclastic flows that can devastate surrounding areas, clearly explosive.
• Strombolian eruption: Involves frequent small to moderate explosive bursts of lava and gas.
• Vulcanian eruption: Characterised by short, violent explosions that throw ash and blocks high into the air.

Common Pitfalls:
Students may confuse Hawaiian and Strombolian eruptions because both can produce lava fountains, but the overall character is different. Another mistake is to pick Pelean or Vulcanian simply because they are less familiar, without recalling their definitions. To avoid confusion, remember that the word Hawaiian should make you think of flowing lava and broad shield volcanoes, which are associated with gentle, effusive activity rather than violent explosions.

Final Answer:
The eruption type that is generally not highly explosive is the Hawaiian eruption.