According to the USGS:

> Mauna Loa is among Earth's most active volcanoes, having erupted 33 times since its first well-documented historical eruption in 1843. It has produced large, voluminous flows of basalt that have reached the ocean eight times since 1868. It last erupted in 1984, when a lava flow came within 7.2 km (4.5 mi) of Hilo, the largest population center on the island. Mauna Loa is certain to erupt again, and with such a propensity to produce large flows, we carefully monitor the volcano for signs of unrest.

Source: https://www.usgs.gov/volcanoes/mauna-loa

Edit: The island is decently big, so the impacts probably won't affect a significant amount of the island. That said, some settlements like Hilo are in the impact zone for a significant event.