While shield volcanoes are known for their gentle slopes and effusive eruptions, they can also produce explosive eruptions and tephra. Here's why:

* Magma Viscosity: Although shield volcanoes are associated with relatively fluid, low-viscosity magma (typically basaltic), magma composition and gas content can vary within a single volcano. Changes in these factors can lead to more explosive eruptions.

* Gas Content: Even fluid magma can hold significant dissolved gas. When this gas expands rapidly as the magma rises to the surface, it can cause powerful explosions.

* Interactions with Groundwater: When magma interacts with groundwater, it can create steam explosions, which are highly explosive and can eject large amounts of tephra.

Examples:

* Kilauea Volcano (Hawaii): While primarily known for its effusive eruptions, Kilauea has produced tephra during explosive eruptions, particularly during its summit caldera collapses.

* Mauna Loa (Hawaii): This massive shield volcano has also experienced explosive eruptions, including ones that produced significant tephra.

Therefore, although less common than effusive eruptions, shield volcanoes can and do summit tephra during explosive events.