Reading this historical report
This page preserves the essential chronology of El Hierro’s volcanic unrest while making clear that its entries describe historical observations, not present-day conditions.
The archive began after heightened seismicity beneath El Hierro in 2011. A submarine eruption later developed south of the island in the Las Calmas Sea. Monitoring continued after the eruptive phase because earthquake swarms, ground movement and volcanic-gas observations can help specialists assess how a volcanic system changes over time.
What the archive records
The original running report followed earthquake locations, magnitudes and depths around El Hierro. It also noted broad deformation trends and periods when activity became quieter. Early interpretations were necessarily provisional; the observations are best read as a chronology rather than a prediction record.
A quiet opening to 2016
The report characterized the preceding period as relatively calm. Only limited seismic activity had stood out in the final days of 2015.
Two deeper earthquakes reviewed
Events of approximately magnitude 3.2 and 2.2 were listed near 34 and 30 kilometres depth. The archive cautioned that a small number of events was insufficient to define a renewed crisis.
Small events west of the island
Several modest earthquakes were logged west and northwest of El Hierro. Their locations were tracked for changes, but no conclusion about escalating activity was drawn.
Deep southwest cluster
Earthquakes were again observed southwest of the island, mostly around 29 to 35 kilometres depth. The archive identified a sustained shift to shallower depths as a pattern that would have required closer evaluation.
Event near the submarine cone area
A magnitude 2.8 earthquake at a reported depth near 12 kilometres was noted in the broader area associated with the earlier submarine eruption. Follow-up observations were needed before interpreting its significance.
Different reported depths
Two events of about magnitude 2.7 and 3.0 were reviewed. The shallower of the pair, reported near 22 kilometres, drew attention because many nearby events had been deeper.
Seismicity and deformation compared
Earthquakes west of the island included an event around magnitude 3.1 at roughly 33 kilometres depth. A western monitoring station showed slight deflation rather than the inflation the archive had considered possible.
Renewed observation period
A short run of deeper western earthquakes prompted renewed attention. The archive explicitly treated any link to rising magma as uncertain rather than established.
Seismicity largely subsided
The second half of November was described as having very limited seismicity, illustrating the intermittent nature of activity after the main unrest.
Felt earthquake west of El Hierro
A magnitude 3.8 event was reported offshore on the island’s western side at approximately 16 kilometres depth. Residents reported feeling the shaking, while the archive noted no corresponding volcanic-tremor signal.
Low-level, intermittent activity
Entries through this period described few earthquakes and no important change in the broad seismic pattern. Quiet intervals were not presented as proof that the system could no longer reactivate.
Context: what the signals mean
Volcano monitoring does not depend on earthquake counts alone. Specialists consider depth migration, event type, deformation, gas chemistry, thermal observations and other measurements together. A deep earthquake may reflect stress adjustment or fluid movement, but it cannot by itself confirm an intrusion or forecast an eruption.
The 2011 event was submarine, meaning eruptive activity occurred below sea level. Offshore volcanic activity can produce unusual water discoloration or surface disturbance, but observations near a suspected vent should be left to monitoring teams and maritime authorities.