It emerged from the ocean about 300,000 years ago and is one of the five volcanoes that make up the island. Its dome, 24 miles (39 km) long and 20 miles (32 km) wide, covers an area of 290 square miles (751 square km). Alkaline eruptions in Hualalai have generally been much less explosive than those at neighboring Kohala and Mauna Kea volcanoes. However, in 1929 an intense earthquake swarm hit Hualalai for a period of one month, which has been interpreted as due to an intrusion of magma near the surface, without a superficial eruption.
No magma-related seismicity or soil deformation has been detected recently in Hualalai, making it difficult to say if and when the next eruption could occur. During this period, no microearthquake swarms or harmonic tremors (both indicative of magma migration) have been recorded, although Hualalai experiences several magnitude 4 earthquakes each year. Although 200 years have passed since the last Hualalai eruption, it is almost certain that it will erupt again. Lava flows represent by far the greatest danger in a possible future Hualalai eruption, because although explosive pyroclastic eruptions have occurred during the Holocene epoch (the last 10,000 years), they are relatively rare and cover only limited parts of the volcano..
