Satellite measurements of recent volcanic activity at Oldoinyo Lengai, Tanzania

Abstract

Oldoinyo Lengai (OL) is the only active volcano in the world that produces natrocarbonatite lava. These carbonate-rich lavas are unique in that they have relatively low temperatures (495-590°C) and very low viscosity. OL has been erupting intermittently since 1983, mostly with small lava flows, pools and spatter cones (hornitos) confined to the summit crater. Explosive, ash-producing eruptions are rare, however, on September 4, 2007 the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) captured the first satellite image of an ash plume erupting from OL, which may be indicative of a new phase of more silica-rich products and explosive activity that has not occurred since [1966][1967]. In the months prior to the eruption, thermal infrared (TIR) satellite monitoring detected an increasing number of thermal anomalies around OL. Data from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor analyzed with the MODLEN algorithm detected more than 30 hot spots in the last week of August and first week of September 2007, some of which were from bush fires ignited by lava flows or spatter around the volcano. Higher-resolution ASTER data confirmed the location of these burn scars associated with lava flows. ASTER also detected the appearance of an anomalous hot spot at the summit of OL in mid-June with temperatures~440°C, the presence of several new lava flows in the crater in July and August, and on September 4 measured higher temperatures (~550°C) possibly suggesting a more silicate-rich eruption. ASTER spectral emissivity data were interpreted to indicate a mixture of carbonate and silicate ash in the eruption plume from September 4. Based on the analysis of both ASTER and MODIS data combined with occasional field observations, there appear to have been 2 distinct eruptive events so far in 2007: a typical natrocarbonatite eruption confined to the summit crater in June-July, and a more intense eruption in August-September consisting of natrocarbonatite lava overflowing the crater and explosive events forming ash plumes up to~5 km high, apparently consisting of a mixture of silicate and carbonate ash. OL is one of the many volcanoes in the world, and especially Africa, that is not regularly monitored with in situ instruments. Continued satellite monitoring along with studies of past thermal activity will help determine how future eruptions and ensuing hazards may be forecasted.

Assessing Performance of the RSTVOLC Multi-Temporal Algorithm in Detecting Subtle Hot Spots at Oldoinyo Lengai (Tanzania, Africa) for Comparison with MODLEN

“…The latter also shows that the analyzed parameter increased in magnitude during 22-25 August because of a documented lava effusion, while it decreased in the following two days (when Q rad was retrieved around 7 MW on MODIS data of 27 August at 22:25 UTC). Afterwards (i.e., during 28-30 August), a new increase in the intensity of thermal emissions was recorded, indicating the possible occurrence of a lava overflow or the presence of an active lava lake within the crater, in agreement with that reported in a previous study [34]. The RGB product from EO1-ALI imagery of 29 August 2007, shown in Figure 5, further confirms this hypothesis.…”

“…Three days later, once again increased reaching about 250 MW (comparable values of this parameter were retrieved on both Aqua and Terra-MODIS scenes), although the radiant flux reached its peak on 1 September, when the lava flowed down the volcano flanks [54]. Since the Afterwards (i.e., during 28-30 August), a new increase in the intensity of thermal emissions was recorded, indicating the possible occurrence of a lava overflow or the presence of an active lava lake within the crater, in agreement with that reported in a previous study [34]. The RGB product from EO1-ALI imagery of 29 August 2007, shown in Figure 5, further confirms this hypothesis.…”

“…Three days later, Q rad once again increased reaching about 250 MW (comparable values of this parameter were retrieved on both Aqua and Terra-MODIS scenes), although the radiant flux reached its peak on 1 September, when the lava flowed down the volcano flanks [54]. Since the voluminous lava overflow triggered some bush fires [34], the maximum Q rad value around 775 MW was presumably overestimated. Nonetheless, this value of the radiant flux appears not particularly high, especially if compared to estimates of same parameter performed in other volcanic areas in presence of active lava flows (e.g., [28]).…”

“…A specific adaption of MODVOLC, named MODLEN, has been designed, tailored and tested with good results for better identifying subtle hot spots at OL [30][31][32][33]. This is not routinely monitored by ground-based systems, as is similar with other African volcanoes [34]. Here we analyze the OL eruptive activity between 2000-2008, through using RSTVOLC, assessing the performance of this largely accepted method for comparison with MODLEN, which may be considered as the benchmark for this volcanic area.…”

Melilite-group minerals at Oldoinyo Lengai, Tanzania

“…In historical times several explosive eruptions interrupted the natrocarbonatite effusive activity, erupting mixed silicate-carbonate ashes (Dawson et al, 1968(Dawson et al, , 1992 and carbonated silicate ashes and lapilli, as in the recent activity phase from September 4th of 2007 through the early summer of 2008 (Mitchell and Dawson, 2007;Vaughan et al, 2008;Reusser and Mattsson, 2008;Keller and Klaudius, 2008;Keller et al, 2010).…”