The seismic focus is the point in the earth's crust where an earthquake originates from.
<span>Downcutting (also known as rejuvenation) of a stream may be due to the uplift of land. It is a process by the action of the hydraulic that makes the channel of the valley or stream by simply get rid of any material on the floor of valleys and streams. Downcutting speed is determined by the base level of the stream. It is the lowermost point that a valley or streams can lose.</span>
Major volcanic events that have occurred within the Ring of Fire since 1800 included the eruptions of Mount Tambora (1815), Krakatoa (1883), Novarupta (1912), Mount Saint Helens (1980), Mount Ruiz (1985), and Mount Pinatubo (1991).
The three means by which the early Polynesian sailors were able to navigate vast regions of the Pacific were by watching the motion of specific stars, weather and seasons of travel and direction, size and speed of ocean waves. The correct options among all the options that are given in the question are option "a", "b", "c".
