Etna Volcanic Tremor: How to Read the INGV Chart

What is Mount Etna's volcanic tremor?

Volcanic tremor is a continuous seismic signal that Etna produces around the clock. It is not the sudden jolt of an earthquake: it is a background vibration, present day and night, linked to the movement of magma and gas inside the volcano's conduits. The seismic stations of the INGV — Osservatorio Etneo record it 24/7, and the institute publishes a near-real-time chart of its amplitude. It is one of the pieces of data I check every morning as a Volcanological Guide before deciding where to take my groups — together with the images of the live Etna webcam, on whose page you will find that same official INGV chart embedded.

In this article I explain how I read that chart and what it really tells you. And, just as important, what it cannot tell you: tremor is not a crystal ball, and assessments of the volcano's activity belong solely to INGV and the Civil Protection, through their official channels. What you will find here is simply an education in reading the data, from someone who works on the volcano every day.

How do you read the INGV tremor chart?

The chart shows the average tremor amplitude recorded by the seismic stations installed around Etna: time runs along the horizontal axis, signal intensity along the vertical one. In practice, the curve tells you how much "seismic noise" the volcano is making, hour by hour.

Three things I have learned to look at, in this order:

• The trend, not the single point. An isolated value says very little: what matters is how the curve moves over hours and days. A line that has stayed low and flat for weeks describes a quiet volcano; a sharp, sustained rise describes a system that is moving more. Between those two extremes lies all of Etna's normal life.
• The comparison with previous days. Etna's "normal" level is not zero: the volcano is always vibrating, even when it looks asleep from the coast. To judge whether a value is high or low you need the context of the previous weeks, not the number of the moment.
• The consistency of the signal. The tremor that matters is the one that persists over time. Local disturbances — strong wind, rough seas, human activity near a station — can pollute the signal: that is why an odd detail on a chart should never be read in isolation.

During the most spectacular episodes of recent years — the lava fountains so many people followed live — the tremor amplitude rose visibly during the episode and fell back as it ended. That is why the chart is so popular among enthusiasts: it is the volcano's "heartbeat", visible to anyone.

What can you NOT deduce from the tremor chart?

This is the part I care about most, because social media is full of misreadings. The tremor chart is not a forecasting tool, and whoever uses it to announce imminent eruptions is making it say things it cannot say.

• It does not tell you when Etna will erupt. No public chart, on its own, does. Assessing volcanic activity relies on many monitoring networks combined — seismic, ground deformation, gas, thermal cameras — and is the exclusive task of INGV.
• A spike is not an eruption. Variations and oscillations are part of the signal's normal life. Reading every rise as an incoming eruption is the surest way to get it wrong.
• It does not tell you where. Tremor is an aggregate signal: the public chart cannot tell you from which vent or flank any activity might appear.
• It is not an alert level. Alert levels and official communications belong only to INGV and the Civil Protection. Be wary of anyone "declaring alarms" by reading a chart: I never do, and I work on this volcano every day.

How I use the tremor as a guide, together with the webcam

My morning routine before every excursion is always the same: I read INGV's official statements and bulletins, I look at the tremor trend, and then I open the webcams to see the volcano with my own eyes — the plume above the summit craters, the clouds, the snow, the visibility. None of these three elements is enough on its own: together, they give me the picture I use to decide the day's route and altitude, always within the limits of the ordinances in force.

The tremor tells me how much "noise" the volcano is making; the webcam shows me what is visible at the surface. If you want to learn to read the images too, I have written a guide on how to read the Etna webcams like a volcanological guide: together with this article, it gives you the same observation tools I use — no shortcuts and no alarmism.

Where to follow Etna's tremor in real time

There is only one source: the INGV — Osservatorio Etneo, which publishes the tremor amplitude chart on its website together with official statements and bulletins. For convenience I also keep it embedded on my webcam page, below the live images, so you can watch the signal and the volcano in the same place. And if you are curious about the whole surveillance machine — seismic networks, thermal cameras, gas measurements — I have described who monitors and studies Mount Etna in a dedicated article.

One last thing, from a guide: read the tremor out of curiosity and for the pleasure of understanding, not to plan your own safety. If you want to climb Etna, the right way is to rely on authorised guides and the rules in force — and the volcano, I promise, is even more fascinating when someone explains it to you up close.

Sources and official references

• INGV — Osservatorio Etneo (ct.ingv.it) — 24/7 monitoring, tremor chart, official statements and bulletins.
• Parco dell'Etna (parcoetna.it) — access rules for the protected area.
• Sicilian Regional College of Alpine and Volcanological Guides — the guides licensed to lead visitors at altitude.