Volcanic Landforms

Types of Volcanoes

Volcanoes are classified by the types of eruption they produce. Broadly speaking, eruptions can be either effusive or explosive. Effusive eruptions are sometimes called "quiet" eruptions (if eruptions can be quiet!). Effusive eruptions are noted for their vast outpourings of very fluid type lava that easily runs across the surface. Explosive eruptions occur as violent explosions of lava and rock fragments that gets stuck in the vent of the volcano. Gases released from the hot magma build to incredible pressure and are released, along with lava, ash and other pyroclastic material, during an explosive eruption. These two types of eruptions create different types of volcanic cones. 

Effusive Eruptions

Effusive eruptions are those that create vast lava flows of low viscosity, fluid lava.   Magma associated with effusive-type eruptions is relatively low in silica and thus "easily" flows up the vent and spreads across the surface. Moving across the land, these lava flows can take on two different forms. Pahoehoe (a Hawaiian term) lava has a glistening, ropy like appearance as it moves and cools.  AA lava is more pasty than pahoehoe and forms a sharp, clinkery, rough surface. As the core of the flow moves across the surface, the rough "clinkers" are carried along the top of the flow. At the leading edge of the flow, the clinkers tumble forward into a heap.

Figure 16.8 View NNW of Mauna Loa, a shield volcano. 
 USGS Click image to enlarge 

Shield volcanoes are a product of effusive eruptions . As the fluid lava flows out onto the surface, it spreads out and cools into a broad, low-angled slope. The final shape looks much like a warrior's shield with the convex side pointing towards the sky. The Hawaiian Islands are an example of shield volcanoes. Though much lava pours from the summit caldera, flank eruptions from lateral vents spreads molten lava along the sides of the volcano. As the lava flow cools, tubes may form in the flow .   These are conduits through which lava flows beneath a skin of solidified lava. Occasionally lava will accumulate as a lava pond or lake too.

Figure 16.9 Shield volcano similar to those found in the Hawaiian Islands

Figure 16.10 Kilauea Volcanic Summit - Drone Video