Although the lava flow is contained mostly within the summit, residents were warned earlier about the possibility of falling ash.
According to the US Geological Service (USGS), the situation could rapidly change.
The alert level for the volcano has been raised from “advisory to “warning”, which is the highest classification.
Emergency officials state that no evacuation orders have been issued, and that populated areas are unlikely be affected at this point.
Mauna Loa is located in Hawaii Volcanoes National Park and covers half the Big Island of the US. It rises to 13,679ft (4.169m) above the sea level and covers an area of over 2,000 miles (5.179 km).
It erupted on Sunday at 23:30 GMT (09:30 GMT Monday) at Moku’aweoweo (the volcano’s summit caldera). Calderas refer to hollows that develop beneath the summit after an eruption.
After a string of warnings about an eruption, it was the result of a number of earthquakes in the area, including several tremors reported on Sunday. Source: US Geological Survey
Overnight, an advisory regarding ashfall was in effect for the area. It can contaminate water supplies and kill vegetation.
The USGS stated that “Based on past events the early stages of Mauna Loa’s eruption can be very dynamic” and that the location and speed of lava flows could change quickly.
It said that lava flows could “move quickly downslope” if the eruption moves beyond the walls of summit caldera.
The USGS reports that Mauna Loa has erupted 33% of the time since 1843. The island’s largest town, Hilo, was 5 miles from the previous eruption of 1984.
However, the Big Island’s population has increased more than twice since 1980 to approximately 200,000 people. Hawaii’s civil defense agency warned that residents could be in danger of a “lava catastrophe”.
Dr Jessica Johnson, a British volcano geophysicist at the University of East Anglia, said that lava flows are rarely a danger to life but can cause severe damage to infrastructure. She has also worked at the Hawaiian Volcano Observatory.
She stated that the lava flows could pose a threat to Hilo and Kona, another important population centre. Additionally, the volcanic gases could cause breathing problems in the locals.
Mauna Loa is considered the largest active volcano in the world. Other larger volcanoes exist, but they are either dormant or extinct. This means they are unlikely to erupt again in the future.
Mauna Loa shares Big Island with Mauna Kea. Mauna Kea is the highest mountain in the world, measured from its underwater base at nearly 20,000 feet below the ocean’s surface.
