Cinder cones can also be distinctly asymmetric if there was a persistent wind blowing during the eruption and/or they form at the heads of major lava flows. In this second instance they are horseshoe-shaped (see below), with the lava flow issuing out of the open end because during the eruption any pyroclasts that landed on the flow were rafted away.
A Mauna Kea cinder cone viewed from the air. A lava flow field (white outline) has issued from the base of the cone, giving the cone an asymmetric form. The flow spread almost all the way around the cone (white arrows). Magenta lines mark the rims of older cinder cones nearby.
Between the two extremes of spatter ramparts and cinder cones are all gradations. Some pyroclastic constructs consist of alternating layers of agglutinate and cinder, indicating that the vigor of the fountaining varied during the eruption. The early part of an eruption, often called the "curtain of fire", produces mostly spatter ramparts and spatter cones. As the activity becomes localized at one or more points along the fissure, this concentration of activity usually leads to higher fountaining. Cinder cones are built at these points, often at the same time that spatter ramparts are forming at the (less active) ends of the fissure. During the Mauna Loa eruption of 1984, there was a distinct gradation from vigorous fountaining at the main vents, progressing to lower and lower fountaining both up and downrift (Lockwood et al. 1987). At the farthest uprift end of the fissure, only gas was being emitted from a spatter cone that had been active earlier in the eruption.