Rarely a serious problem. Look-alikes: Jumping oak gall, tubakia leaf spot, oak leaf blister, other fungal leaf spots. Jumping oak gall Brown leaves appear on trees in the white oak group in late spring. Severe infections may cause the leaves to turn black, curl up and fall. On the underside are brown galls with the larva of a small wasp inside.
Volcanoes form when magma reaches the Earth's surface, causing eruptions of lava and ash. They occur at destructive (compressional) and constructive (tensional) plate boundaries. The immediate effects of volcanic eruptions can be devastating, but they may be beneficial in the long term.
Why do volcanoes form at convergent boundaries instead of divergent boundaries? Volcanoes form at both convergent and divergent boundaries. At convergent boundaries (except those involving two continental plates) one plate slides under another, introducin â¦ g volatiles into the mantle, which allows some of it to melt and rise to form volcanoes. At divergent plate boundaries the young, thin crust reduces pressure on the upper mantle, reducing melting points and allowing magma to form. However, most volcanoes at divergent boundaries are deep underwater and so they ...