Complex sentence: Pyroclastic surges are much faster moving than pyroclastic flows, and can reach speeds of 350 km/h. Pyroclastic flows may generate surges, for example the city of Saint-Pierre on the Caribbean island of Martinique in 1902 was overcome by one.
Split into simpler sentences: Pyroclastic surges are much faster moving than pyroclastic flows, and can reach speeds of 350 km/h. Pyroclastic flows may generate surges. For example the, city of Saint-Pierre on the Caribbean island of Martinique in 1902 was overcome by one.