Superheated steam and ash from Krakatoa's main blast killed and burned people 30 to 40 miles away on the Sumatra coast. Krakatoa also spawned tidal waves over 100 feet high that swept the coasts of Java and Sumatra, claiming most of the 37,000 lives lost in that eruption. Major eruptions are incredibly loud. Noises from the eruption of Tambora in Indonesia in 1815 were mistaken for nearby canon fire in European settlements 200 and 750 miles away from the volcano itself. If the main eruption of Mount St. Helens had made as much sheer noise as Tambora, it would have been heard all over the United States.
Major eruptions can affect weather around the world.
Clouds of ash and sulfur-rich particles thrown into the stratosphere by large volcanic blasts reflect part of the sunlight reaching Earth, causing cooling of the atmosphere. The larger the blast, the greater the effect. A global cooling of about 1.5 deg. Cold temperatures and killing frosts in Europe and New England in America caused extensive crop failures and resulted in famine in post-Napoleonic France. Major eruptions have even been responsible at times for literally changing the course of history.