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June 30, 2022

Heraklion is the largest city on the island of Crete in Mediterranean Sea. The island isn’t volcanic, but other Greek islands dotting the sea surface nearby are, and the city recently hosted a “Cities on Volcanoes” scientific meeting.  

Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.

During June 12–17, USGS volcano scientists, including three from the Hawaiian Volcano Observatory, gave talks, presented research, convened sessions, attended workshops, and facilitated discussions both in person and virtually at this meeting (  

Cities on Volcanoes meetings are sponsored by the International Association of Volcanology and Chemistry of the Earth's Interior, a society of scientists from around the world that specialize in volcanology and related disciplines. 

The recent meeting in Crete is the 11th in a series of “Cities on Volcanoes” meetings that began in 1998. These meetings, hosted in communities impacted by volcanic processes, bring together volcano scientists and emergency responders with the goal of promoting these different perspectives to better understand volcanoes and lessen their impact on communities. 

USGS scientists at the recent Cities on Volcanoes meeting presented on a range of topics, including dynamics and responses to recent eruptions, such as the 2018 Kīlauea and 2022 Hunga Tonga-Hunga Ha’apai eruptions, developing emergency-preparedness, eruption, and response plans, developing hazard zones and hazard assessments, using new tools for eruption monitoring, new insights gained from looking at eruption deposits, and compilations of official information on volcanic activity.  

Previous Cities on Volcanoes meetings were held in other countries with cities on or near active volcanoes: Italy, New Zealand, the United States, Ecuador, Japan, Spain, Mexico, Indonesia, and Chile. The third Cities on Volcanoes meeting was appropriately hosted in Hilo, Hawaii, in 2003!  

Color photograph of lava flow
Rubbly ‘a‘ā from the 1855–56 Northeast Rift Zone eruption of Mauna Loa dominates the foreground of this image, taken from a pull-off of the Saddle Road on June 26, 2022. This lava flow bypassed some vegetation, forming the forested kīpuka in the middle of the image. The slopes of Mauna Loa are visible in the background, amongst a cloudy sky. USGS photo by K. Mulliken.

Why was Hilo chosen as the host of the third Cities on Volcanoes meeting? Hilo town is built on the northeast slopes of the massive volcano Mauna Loa: it is a city on and affected by a volcano. Over the past couple of centuries, lava flows from the Northeast Rift Zone of Mauna Loa have flowed downslope towards Hilo in 1984, 1942, 1935–1936, 1880–81, 1855–56, and 1852. 

These lava flows are easily visible as you drive the Daniel K. Inouye Highway across the center of the Island of Hawai‘i (Hawaii Route 200, also known as the Saddle Road). Their dark colors and lack of vegetation attest to their young ages. The flows created a patchwork of vegetated kīpuka through which several Nā Ala Hele trails meander ( 

Guatemala, in Central America, will host the next Cities on Volcanoes gathering in February of 2024. Guatemala has over 20 volcanoes, two of which have erupted this year: Santa Maria and Volcán de Fuego. 

No volcanoes in Greece are currently erupting; however, the picturesque town of Santorini is on the largest of several islands that formed during the caldera-forming eruption of Santorini volcano roughly 3,600 years ago. 

Prior to the eruption, the island was much larger, known as Thera, and inhabited by members of the Minoan Civilization. The eruption is sometimes referred to as the Minoan eruption as it occurred during the peak of the Minoan Civilization, a society known for its construction of paved roads, advanced ships, and the first in Europe to use a written language.  

The caldera that formed during the eruption is mostly submerged. The surrounding islands represent the highest parts surrounding the caldera, above the sea surface. The eruption was large enough to cause a tsunami that affected the nearby island of Crete. Work by archaeologists suggest that the fall of the Minoans might have been related to the legend of Atlantis—a city that was lost to water.  

Like Heraklion and other hosts of Cities on Volcanoes meetings, Hilo remains a city affected by volcanoes. This is sometimes easy to forget given the decades since the last encroaching lava flow. If you find yourself roaming the streets of Hilo, remember that the patchwork of lava flows and kīpuka upslope are a reminder of past eruptions.  


Volcano Activity Updates


Kīlauea volcano is erupting. Its USGS Volcano Alert level is at WATCH ( Kīlauea updates are issued daily.    

Over the past week, lava has continued to erupt from the western vent within Halemaʻumaʻu crater. All lava is confined within Halemaʻumaʻu crater in Hawai‘i Volcanoes National Park. Sulfur dioxide emission rates remain elevated and were last measured at approximately 1,200 tonnes per day (t/d) on June 29. Seismicity is elevated but stable, with few earthquakes and ongoing volcanic tremor. Summit tiltmeters recorded deflation at the start of the week, relatively little deformation throughout the week, and inflation beginning the morning of June 30. For more information on the current eruption of Kīlauea, see

Mauna Loa is not erupting and remains at Volcano Alert Level ADVISORY. This alert level does not mean that an eruption is imminent or that progression to an eruption from the current level of unrest is certain. Mauna Loa updates are issued weekly.     

This past week, about 93 small-magnitude earthquakes were recorded below the summit and upper elevation flanks of Mauna Loa—the majority of these occurred at shallow depths less than 15 kilometers (9 miles) below sea level. Global Positioning System (GPS) measurements show low rates of ground deformation over the past week. Gas concentrations and fumarole temperatures at both the summit and at Sulphur Cone on the Southwest Rift Zone have remained stable over the past week. Webcams show no changes to the landscape. For more information on current monitoring of Mauna Loa, see:  

Five earthquakes were reported felt in the Hawaiian Islands during the past week: a M3.5 earthquake 9 km (5 mi) ENE of Pāhala at 32 km (20 mi) depth on June 29 at 11:50 a.m. HST, a M3.7 earthquake 0 km (0 mi) E of Pāhala at 35 km (21 mi) depth on June 28 at 1:25 p.m. HST, a M3.4 earthquake 27 km (16 mi) SSE of Waimea at 13 km (8 mi) depth on June 28 at 12:38 a.m. HST, a M3.3 earthquake 3 km (1 mi) SSW of Pāhala at 34 km (21 mi) depth on June 26 at 6:51 p.m. HST, and a M3.6 earthquake 4 km (2 mi) SSW of Pāhala at 36 km (22 mi) depth on June 23 at 9:19 a.m. HST.

HVO continues to closely monitor Kīlauea's ongoing eruption and Mauna Loa for any signs of increased activity.    

Please visit HVO’s website for past Volcano Watch articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake info, and more. Email questions to    

Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.