What is the term for a fast-moving current of hot ash, gas, and rock that flows down the side of a volcano?

Which strait connects the Sea of Azov to the Black Sea? What strait separates the islands of Luzon and Mindoro in the Philippines? What strait separates the islands of Java and Madura in Indonesia? What strait separates the islands of Borneo and Sumatra in Indonesia? Which of the following volcanoes is known for its perfectly symmetrical cone shape? Which volcanic feature is formed by the collapse of a volcano's cone? Which of the following volcanoes is located in the Andes mountain range? Which of the following volcanoes is located in the Pacific Ring of Fire?