Eruption Precursors Research Articles

Precursors to eruption

Precursors to eruption

Gravity changes as a precursor to volcanic eruption at Poás volcano, Costa Rica

MONITORING of gravity changes at active volcanoes has considerable potential for understanding magma-chamber dynamics and for detecting eruptive precursors. The technique essentially aims to identify changes in sub-surface mass or density corresponding to departures from the free-air gradient (FAG) or Bouguer-corrected (terrain-corrected) FAG (BCFAG), respectively1,2. Such gravity changes, of the order of 10–100 µgal, have been reported previously through eruptive periods3–6. Here we present a ten-year data set measured at Poas volcano, Costa Rica, in which gravity increases in 1987–1989, relative to both the FAG and the BCFAG, preceded the ash-cloud eruptions of April–May 1989. These results constitute the first unambiguous detection of gravity changes as a precursor to eruption, and we interpret them in terms of the intrusion of an ascending, relatively dense magma body.

Recent seismic activity of the Kivu Province, Western Rift Valley of Africa

The Kivu Province is located at the junction between the well-defined Ruzizi Valley to the south and the Lake Amin Trough to the north. In this zone, the Rift Valley is characterized by the highest uplift and by complex dislocations of the crust, accompanied by the most intensive volcanism of the East African Rift System. In this paper, we show the recent state of the seismic activity of this zone in connection with the seismic activity generated by the volcanoes Nyiragongo and Nyamuragira. The pattern of cumulative energy release by these volcanoes shows a steplike increase that is believed to be a precursor of volcanic eruptions.

Thermal activity and ground deformation at Phlegrean Fields, Italy: Precursors of eruptions or fluctuations of quiescent volcanism? A contribution of geochemical studies

The ground uplift that occurred at Phlegrean Fields during the “crisis” of 1982–1984 is analyzed by taking into account the volcanological history of the area, the available geophysical information, and the data obtained through our systematic geochemical study. The chemical composition of the products of a unique historical eruption in A.D. 1538 displays a strong evolved character and fits the hypothesis of a progressive reduction in size of the magma body, which probably behaved as a closed system. The bicarbonate contents of the thermal waters in the area has increased with time, suggesting inputs of carbon dioxide into the shallow aquifers. Temperatures at the fumaroles have not changed for at least a hundred years, indicating that boiling aquifer at depth feeds the surface manifestations. Significant variations in the ratios H2S/CO2 and H2/N2 observed at the same time suggest that both the rate of ground uplifting and the increase of seismic energy release may be related to the fluctuation of a convective flow from a deep heat source. Tectonic activity can modify the permeability of deep structures and thereby trigger increased activity in surface manifestations.

Volcano hazards program in the United States

Volcano monitoring and volcanic-hazards studies have received greatly increased attention in the United States in the past few years. Before 1980, the Volcanic Hazards Program was primarily focused on the active volcanoes of Kilauea and Mauna Loa, Hawaii, which have been monitored continuously since 1912 by the Hawaiian Volcano Observatory. After the reawakening and catastrophic eruption of Mount St. Helens in 1980, the program was substantially expanded as the government and general public became aware of the potential for eruptions and associated hazards within the conterminous United States. Integrated components of the expanded program include: volcanic-hazards assessment; volcano monitoring; fundamental research; and, in concert with federal, state, and local authorities, emergency-response planning. In 1980 the David A. Johnston Cascades Volcano Observatory was established in Vancouver, Washington, to systematically monitor the continuing activity of Mount St. Helens, and to acquire baseline data for monitoring the other, presently quiescent, but potentially dangerous Cascade volcanoes in the Pacific Northwest. Since June 1980, all of the eruptions of Mount St. Helens have been predicted successfully on the basis of seismic and geodetic monitoring. The largest volcanic eruptions, but the least probable statistically, that pose a threat to western conterminous United States are those from the large Pleistocene-Holocene volcanic systems, such as Long Valley caldera (California) and Yellowstone caldera (Wyoming), which are underlain by large magma chambers still potentially capable of producing catastrophic caldera-forming eruptions. In order to become better prepared for possible future hazards associated with such historically unpecedented events, detailed studies of these, and similar, large volcanic systems should be intensified to gain better insight into caldera-forming processes and to recognize, if possible, the precursors of caldera-forming eruptions.

A Review on the Chemical Precursors of Volcanic Eruptions

A Review on the Chemical Precursors of Volcanic Eruptions

Eruption forecasting at Kilauea Volcano, Hawaii

Data from a network of seismometers, a tiltmeter and the pattern of summit inflation between eruptions have made qualitative eruption forecasting possible on Kilauea volcano for over 20 years. This paper formulates quantitative forecasting by calculating the probability of an eruption based on current levels of tilt, tilt rate, seismicity, and fortnightly tide. Plots of eruption probability as a function of various parameters are derived using a set of 29 eruptions during 1959–1979. The method tests the precursory significance of various parameters over different time scales and determines probabilities by comparing data before eruptions with data values generally. Tilt level is an eruption precursor significant to better than 99.9% when averaged over any interval from 1 to 20 days. Tilt rate is a precursor significant to better than 99.999%, but noise in the data requires that it be averaged over 30 days or more. Earthquakes are a short‐term precursor significant to better than 99% when averaged over 1–10 days for larger earthquakes near the summit caldera and over 5–20 days for very small earthquakes within the caldera. The fortnightly modulation of tides influences eruption probability and has a precursory significance of 97%. Probabilities are independent of the time elapsed since the last eruption. The eruption probability, when tested against the eruption record from which it was derived, is significant to the 99.98% level when compared with random guessing. Ongoing 1‐day, 7‐day, and 30‐day forecasts are calculated by computer at the Hawaiian Volcano Observatory and supplement the qualitative interpretation of geophysical data.