Mauna Loa is stirring. This week more “swarms” of small earthquakes shook the Hawaiian peak, following an increase in seismic activity on the summit for months. These earthquakes may mean that the largest volcano in the world is waking up, which could mean the first eruption of Mauna Loa since 1984.

Now, you may be thinking, “Hey, didn’t the volcano in Hawaii have a significant eruption just a few years ago? Isn’t it erupting, sort of right now?” And yes, you’re right, Kīlauea is currently actively erupting and has been for many decades. And there was a huge eruption in 2018 (pictured) that flattened an entire residential neighborhood and displaced 2000 people while adding over 800 acres of land to the Big Island. But Kīlauea is not the same as Mauna Loa.

The Big Island of Hawaii is made up of five separate volcanos: Kīlauea, Mauna Loa, Mauna Kea, Hualālai, and Kohala. Kohala is extinct and Mauna Kea is classified as dormant and has not erupted for several thousand years, but the rest of the volcanoes are still active, including a sixth volcano that’s still underwater, the seamount of Lō‘ihi.

Kilauea is the most active volcano in the world and was home to a continuous eruption at the Puʻu ʻŌʻō crater from 1983 to 2018. On the other hand, Mauna Loa, which makes up half of the big island, is the largest mountain in the world and the largest active volcano. It has erupted 33 times since 1843 but has not seen any eruptions or active lava flow from the summit crater, known as Moku‘āweoweo Caldera, since 1984.

All of this activity, and in fact, the entire existence of the Hawaii island chain, is due to the Pacific plate of the earth’s crust slowly drifting across a hot spot in the earth’s mantle by a few inches a year, which adds up to around 32 miles per million years. The magma rising from the hot spot pushes up and out of the shield-type volcanoes of Hawaii, constantly growing the islands. As the magma and gases beneath the volcanoes rises and releases, it makes the earth move. So more earthquakes are an indicator of another eruption possibly coming. Before previous eruptions, there have been big seismic spikes.

The Mauna Loa eruption in 1984 was massive and intense, with lava flows threatening the largest population center on the Big Island, the city of Hilo. The lave stopped only 7 miles from the city, which was lucky. Now that Mauna Loa is stirring again, the Hawaiian Volcano Observatory at the USGS is reminding residents “now is the time to revisit personal eruption plans.  Similar to preparing for hurricane season, having an eruption plan in advance helps during an emergency.”

And depending on where and how an eruption on Mauna Loa happens, there’s a big difference in the speed at which lava flows could reach different areas, as shown by this map from the USGS.

Now, the seismic activity on Mauna Loa right now is nothing compared to 1984, or other eruptions … yet. But with these volcanoes, it’s very much a matter of “when” and not “if” they will erupt again, given the continuing activity on Mauna Loa, as well as other Hawaiian volcanoes.

It’s worth noting that we can’t even be sure where a lava flow might come from. The lava flows from the Kilauea eruption in 2018 didn’t flow from the famous crater but from dozens of fissures that opened in a residential neighborhood. Scientists can hope to predict and prepare for these eruptions, and warn people to stay on alert, but there’s a saying in Hawaii about the goddess of the volcano that was shared with me by a friend who studied the volcanoes there: “Pele goes where she wants.” When Pele starts to move, all we can do is get out of the way and hope she gives some warning.

(via: Maui Now, image: Mario Tama/Getty Images)

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The post Mauna Loa, the World’s Largest Volcano, May Be Waking Up first appeared on The Mary Sue.