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.
Others are formed when the summit of a volcano collapses into an empty magma cavern that had stored the magma prior to eruption. Shield Volcanoes. Shield volcanoes, formed when large flows of lava spread rapidly from central vents or rows of vents, are the largest volcanoes.Because the lava moves rapidly and spreads out in a broad area, it does not form a tall, steep cone. Instead, shield volcanoes are dome-shaped mountains with broad bases and gentle slopes.tratovolcanoes, or composite volcanoes, get their name from the different layers, or strata, of ash and lava that form them. Most stratovolcanoes are irregularly shaped mountains formed by material ejected from both a central vent and other vents on the sides of the mountain.