But the plume is not a straight pipe as some concept figures suggest. Instead, it has twists and turns, originally coming from the southeast, but then turning toward the west of Hawaii as the plume reaches into the shallower mantle. Cracks in the Pacific Plate then channel the magma upward toward the magma chamber beneath the island of Hawaii.

Hawaii is in the middle of an oceanic plate. In fact, it is the most isolated volcanic hot spot on Earth, far away from any plate boundary.

Oceanic magma is very different from continental magma. It has a different chemical composition and flows much more easily. So, the magma is less prone to clog volcanic vents on its ascent, which would ultimately lead to more explosive volcanism.

Volcanic activity is monitored with many different instruments.

The perhaps simplest to understand is GPS. The way scientists use GPS is different from that of everyday life. It can detect minuscule movements of a few centimeters. On volcanoes, any upward movement on the surface detected by GPS indicates that something is pushing from underneath.

Even more sensitive are tiltmeters, which are in essence the same as bubble levels that people use to hang pictures on a wall. Any change in the tilt on a volcano slope indicates that the volcano is “breathing,” again because of magma moving below.

A very important tool is watching for seismic activity.

Volcanoes like Hawaii’s are monitored with a large network of seismographs. Any movement of magma below will cause tremors that are picked up by the seismometers. A few weeks before the eruption of Mauna Loa, scientists noticed that the tremors came from ever shallower depths, indicating that magma was rising and an eruption might be imminent. This allowed scientists to warn the public.

Other ways that volcanic activity is monitored includes chemical analysis of gases coming out through fumaroles – holes or cracks through which volcanic gases escape. If the composition changes or activity increases, that’s a pretty clear indication that the volcano is changing.

This article is republished from The Conversation, an independent nonprofit news site dedicated to sharing ideas from academic experts. It was written by: Gabi Laske, University of California, San Diego. Like this article? subscribe to our weekly newsletter.

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Gabi Laske receives funding from the National Science Foundation.