VSI reported that the Marapi eruption at 0814 on 16 April produced a cauliflower-shaped black ash plume that rose 2 km above the summit. Ash, lapilli, and volcanic bombs were ejected during the eruption and fell within the crater. In addition, ash fell in many villages on the S and SW flanks of the volcano. Within 1-4 km from the summit the thickness of the ash deposits was between 2 and 3 cm. Until 18 April approximately 150 smaller explosions continuously occurred. The 16 April eruption was preceded by shallow volcanic earthquakes that began on 7 April and by continuous volcanic tremor recorded on 9 April. Small eruptions occurred at 1283 and 1600 on 13 April. VSI had increased the Alert Level at Marapi from 1 to 2 following the minor activity that began on 13 April.

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)

INETER personnel reported that volcanic activity at Masaya decreased following the 23 April explosion. Small explosions were observed on 24 and 25 April, but by 27 April only the continuous emission of gas at normal levels was observed with few episodes of strong degassing. Likewise, after the 23 April explosion the level of SO₂ emission decreased and normal levels of seismic activity were recorded. INETER warned that further explosions may occur that could affect areas near the crater (within ~500 m).

A tourist at the scene during the 23 April explosion stated that injuries were more serious than was reported either here or in news accounts. Over 100 tourists were near the crater when the explosion occurred, including infants and elderly persons. At least 15 people sustained injuries (bruises and cuts) and one person suffered a broken arm.

Source: Instituto Nicaragüense de Estudios Territoriales (INETER)

Following the sharp increase in seismic activity on 22 April the number and magnitude of seismic events continued to increase at Shiveluch until 27 April. The largest earthquake occurred on 27 April (M 4) and the number and magnitude of earthquakes began to slightly decrease on 28 April. Several gas-and-steam plumes that reached a maximum height of 700 m above the volcano were observed starting on 28 April. As of 1 May seismic activity was still significantly above background levels. KVERT stated that the trend of the seismic activity is similar to the increase that preceded the violent 1993 eruption. The Concern Color Code at Shiveluch remained at Orange.

Source: Kamchatkan Volcanic Eruption Response Team (KVERT)

According to the Darwin VAAC, a pilot reported observing a "smoke" cloud produced from Ulawun at 0730 on 30 April. The cloud was at an altitude of ~9 km a.s.l. and drifting to the NW and SW. Satellite imagery indicated that the cloud may have reached ~13.7 km a.s.l. and that the eruption ceased by ~1530 on 30 April. The Rabaul Volcanological Observatory stated that Ulawun is at a high alert level and further eruptions are possible.

Source: Darwin Volcanic Ash Advisory Centre (VAAC)

Volcanic unrest continued at Cleveland through 27 April. During this time a thermal anomaly was observed on satellite imagery when weather permitted. Low pulses of volcanic tremor continued to be detected by an AVO seismic network 230 km to the E of the volcano. AVO had received no reports of significant volcanic activity from either pilots, residents, or satellite remote-sensors since the last eruption on 19 March.

Source: US Geological Survey Alaska Volcano Observatory (AVO)

According to the Italy's Volcanoes website, activity at Etna's summit craters progressively increased beginning on about 20 April. Lava effusion from a vent on the lower NNE flank of Southeast Crater cone continued, with an increase in the effusion rate on 26 April. Ash vented from Bocca Nuova and light gas was emitted from a vent on the NNE flank of Southeast Crater.

Source: Italy's Volcanoes

During 16-23 April there was an increase in the number of shallow volcanic earthquakes (ten) in comparison to the previous week. Seismographs also recorded one deep volcanic, and two tectonic earthquakes. The volcano remained at Alert Level 2 (on a scale of 1-4).

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)

VSI reported that during 16-23 April seismic activity increased at Inielika in comparison to the previous week. Seismographs recorded five deep volcanic, ten shallow volcanic, and eleven tectonic earthquakes. Inielika is at Alert Level 2 (on a scale of 1-4). The previous report of significant volcanic activity occurred on 11 January 2001 when minor explosions began.

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)

During 16-23 April lava flowed from crater I to a maximum distance of 50 m, and lava avalanches often originated from the end of the lava flow and traveled about 750 m to the Nanitu River. In addition, a medium-gray plume that likely contained ash rose 50-300 m above the main crater, and a possible steam cloud from crater II rose 200 m above the summit. A red-colored reflection was visible rising 25 m above the volcano. Karangetang remained at Alert Level 2 (on a scale of 1-4).

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)

Lava continued to flow down the Pūlama pali and across the coastal flat. On 25 April a small stream of lava reached the sea for the first time since late January. The lava stopped trickling into the sea on 29 April. On that day an unstable block of the lava bench fell into the sea, producing a loud noise and generating an explosion that tossed rocks onto dry land. A M 4.4 earthquake on the afternoon of 25 April was followed by a few small aftershocks during the rest of the week. A swarm of long-period earthquakes that began on 18 April continued through at least 27 April. The tilt at the summit was neither flat nor consistently in one direction or the other. Tiltmeters along the east rift zone indicated that there was no significant deformation.

Source: US Geological Survey Hawaiian Volcano Observatory (HVO)

PHIVOLCS reported that during the week ending on 22 April there had been a total of 42 low-frequency earthquakes and 11 high-frequency short-duration harmonic tremors. The SO₂ flux during the same period averaged 3,400 metric tons/day, which is still significantly above the baseline value of 500 tons/day. Deformation monitoring showed that the volcano was inflated, but the present trend revealed insignificant change. Moderate steaming was typical. The crater was visible, but no glow was observed. Alert Level 3 remained in effect, prohibiting entry within the 6-km-radius permanent danger zone.

Source: Philippine Institute of Volcanology and Seismology (PHIVOLCS)

During 16-23 April lava avalanches continued to flow down the Sat, Senowo, Lamat, and Bebeng rivers, with a maximum runout distance of 2 km. Fumaroles emitted gas that rose up to 500 m above the summit. Seismic activity continued to be dominated by avalanche earthquakes. Merapi remained at Alert Level 2 (on a scale of 1-4).

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)

CENAPRED reported that at 0819 on 29 April a moderate explosion occurred at Popocatépetl that lasted for 1 minute and produced an ash cloud that rose 2 km above the volcano's summit and drifted to the ENE. A pilot reported that the ash cloud reached an altitude of 9 km a.s.l. Light ash fall was reported in San Pedro Benito Juárez ~10 km SE of the volcano's summit. Throughout the day several episodes of harmonic tremor occurred. Based on information from the Mexico City MWO, the Washington VAAC reported that another eruption occurred later the same day at 1310. It produced an ash cloud that rose 6.7-7.6 km a.s.l. The volcano remained at Alert Level Yellow Phase III, with a restricted 12-km-radius area.

Sources: Washington Volcanic Ash Advisory Center (VAAC), Associated Press, Centro Nacional de Prevencion de Desastres (CENAPRED)

Volcanic activity increased at Semeru in comparison to the previous week, with an increase in explosion and deep volcanic earthquakes. Seismographs recorded 550 explosion events, 149 avalanche events, and ten tectonic earthquakes. Gas explosions rose up to 300 m above the volcano. Semeru remained at Alert Level 2 (on a scale of 1-4).

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)

MVO reported that during 20-27 April volcanic activity at Soufrière Hills remained low, with few rockfalls and little seismicity. A very small amount of growth occurred on the S side of the lava dome, which was accompanied by occasional ash venting. Sulfur dioxide flux also remained low.

Source: Montserrat Volcano Observatory (MVO)

Based on information from the IG, the Washington VAAC reported that several small eruptions occurred at Tungurahua and that lahars were active in several sectors of the volcano. At 1600 on 25 April a pilot reported that ash was visible over the volcano at an altitude of ~7 km. Seismic activity indicated that brief eruptions occurred at 1230 on 28 April and at 1130 on 29 April, but extensive cloudiness prevented observations of the ash clouds. On 29 and 30 April lahars traveled to the Pampas, Cusuá, Hacienda, and Achupashal sectors and the river levels rose in the Ulba and Mandur sectors. The lahars in the Pampas sector blocked the Pelileo-Baños channel during 0710 to 1100 on 29 April and destroyed the highway. The IG warned that rainy conditions may cause more lahars and rising river levels near the volcano.

Sources: Instituto Geofísico-Escuela Politécnica Nacional (IG-EPN), Washington Volcanic Ash Advisory Center (VAAC)