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.
Key facts. 1  A volcano is formed by eruptions of lava and ash. 2  Volcanoes are usually cone shaped mountains or hills. 3  When magma reaches the Earth's surface it is called lava. When the lava cools, it forms rock. 4  Volcanic eruptions can happen at destructive and constructive boundaries, but not at conservative boundaries.