A small rootless shield approximately 10 to 15 m (33 to 49 feet) high. Photo taken looking SSW, with the upslope direction to the right. May 27, 2010
A small rootless shield approximately 10 to 15 m (33 to 49 feet) high. Photo taken looking SSW, with the upslope direction to the right. May 27, 2010
A rootless shield is one of several shield-shaped features found on Hawaiian volcanoes, such as Kilauea and Mauna Loa, which are themselves referred to as shield volcanoes.
Rootless shields form on active lava flows or lava tubes, and are fed by lava that is flowing on or just below the surface. They are called "rootless," because their source lava is not directly from a vent that is connected to a deep conduit or magma reservoir. Rootless shields are typically smaller than the shield-shaped features that form on active vents fed by deeper rift zone lava.
Rootless shields are low-lying features. They can be difficult to spot from the air, but their broad, gently domed shape is unmistakable from the ground. They are commonly several hundred meters (yards) across, but only tens of meters (yards) high.
An important consequence of rootless shields is that their construction can slow or prevent the downhill flow of lava. In other words, because more lava is consumed by shield-building, less lava is available to feed forward-moving flows. This is good news for communities downslope.
On the other hand, rootless shields are not entirely stable. Like water dams, their flanks can rupture or collapse, disgorging fluid lava from their molten interiors and feeding fast-moving flows.
Also see the HVO Volcano Watch article, Rootless Shields are not a Gang of Nomadic Warriors.