Global Volcanism Program

Most Recent Bulletin Report: September 1998 (BGVN 23:09) Cite this Report

Seismic swarm on submarine flank

Since June 1998, increasing seismic activity in the vicinity of Sete Cidades volcano has resulted in occasional seismic swarms. On the night of 2-3 August about 120 events were registered in 3 hours. During that period, five earthquakes were felt along the W coast, the strongest with a magnitude of 3.1 reached a maximum intensity of V (MM) at Ginetes e Varzea. Similarly, on 2 September in Sao Miguel more than 120 events occurred beneath the sea floor over a period of about 4 hours near shore between Ponta da Ferraria and Mosteiros. One of the five felt earthquakes during this period also reached an intensity of V (MM). There were no reports of injury or damage from any of these events.

Information Contacts: João Luis Gaspar and Nicolau Wallenstein, Departamento de Geociencias, Centro de Vulcanologia, Universidade dos Açores, Rua Mae de Deus, 9500 - Ponta Delgada, Sao Miguel, Açores, Portugal.

The Global Volcanism Program has no Weekly Reports available for Sete Cidades.

Bulletin Reports - Index

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

09/1998 (BGVN 23:09) Seismic swarm on submarine flank

Information is preliminary and subject to change. All times are local (unless otherwise noted)

September 1998 (BGVN 23:09) Cite this Report

Seismic swarm on submarine flank

Since June 1998, increasing seismic activity in the vicinity of Sete Cidades volcano has resulted in occasional seismic swarms. On the night of 2-3 August about 120 events were registered in 3 hours. During that period, five earthquakes were felt along the W coast, the strongest with a magnitude of 3.1 reached a maximum intensity of V (MM) at Ginetes e Varzea. Similarly, on 2 September in Sao Miguel more than 120 events occurred beneath the sea floor over a period of about 4 hours near shore between Ponta da Ferraria and Mosteiros. One of the five felt earthquakes during this period also reached an intensity of V (MM). There were no reports of injury or damage from any of these events.

Information Contacts: João Luis Gaspar and Nicolau Wallenstein, Departamento de Geociencias, Centro de Vulcanologia, Universidade dos Açores, Rua Mae de Deus, 9500 - Ponta Delgada, Sao Miguel, Açores, Portugal.

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.

Cones

Feature Name

Feature Type

Elevation

Latitude

Longitude

Alferes, Caldeira do

Cone

450 m

37° 52' 0" N

25° 48' 0" W

Boi, Pico do

Cone

542 m

37° 49' 0" N

25° 43' 0" W

Camarinhas, Pico das

Cone

219 m

37° 51' 0" N

25° 51' 0" W

Carvao

Cone

815 m

37° 49' 0" N

25° 44' 0" W

Cavalo, Pico do

Cone

215 m

37° 51' 0" N

25° 51' 0" W

Cedro, Pico do

Cone

387 m

37° 49' 0" N

25° 42' 0" W

Cruz, Pico da

Cone

850 m

37° 51' 0" N

25° 46' 0" W

Eguas

Cone

873 m

37° 50' 0" N

25° 45' 0" W

Enforcado, Pico do

Cone

338 m

37° 48' 0" N

25° 41' 0" W

Ferrarias

Cone

37° 50' 0" N

25° 46' 0" W

Ilheu Dos Mosteiros

Cone

37° 55' 0" N

25° 50' 0" W

Mafra, Pico de

Cone

360 m

Mulata

Cone

373 m

37° 48' 0" N

25° 42' 0" W

Pilar, Lagoa do

Cone

332 m

37° 54' 0" N

25° 47' 0" W

Seara Cerrado de Ladeira

Pyroclastic cone

475 m

37° 52' 0" N

25° 48' 0" W

Varzea, Pico do

Cone

275 m

37° 52' 0" N

25° 50' 0" W

Craters

Feature Name

Feature Type

Elevation

Latitude

Longitude

Alferes, Caldeira do

Pumice ring

583 m

37° 52' 0" N

25° 48' 0" W

Canario, Lagoa do

Maar

811 m

37° 50' 0" N

25° 46' 0" W

Rasa, Lagoa

Pumice ring

625 m

37° 51' 0" N

25° 46' 0" W

Santiago, Lagoa de
Sao Tiago, Lagoa de

Pumice ring

616 m

37° 51' 0" N

25° 46' 0" W

Scara

Pit crater

37° 52' 0" N

25° 48' 0" W

Seca, Caldeira

Pumice ring

375 m

37° 51' 0" N

25° 48' 0" W

Basic Data

Volcano Number

Last Known Eruption

Elevation

Latitude
Longitude

382080

1880 CE

856 m / 2808 ft

37.87°N
25.78°W

Volcano Types

Stratovolcano
Caldera
Pyroclastic cone(s)

Rock Types

Major
Trachyte / Trachydacite
Trachybasalt / Tephrite Basanite
Basalt / Picro-Basalt
Trachyandesite / Basaltic Trachyandesite

Tectonic Setting

Rift zone
Oceanic crust (< 15 km)

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km

3,515
10,365
102,848
127,154

Geological Summary

Sete Cidades volcano at the western end of Sao Miguel Island contains a 5-km-wide summit caldera, occupied by two caldera lakes, that is one of the scenic highlights of the Azores. The steep-walled, 500-m-deep caldera was formed about 22,000 years ago, and at least 22 post-caldera eruptions have occurred. A large group of Pleistocene post-caldera trachytic lava domes, lava flows, and pyroclastic-flow deposits is found on the western-to-northern flanks. A nearly circular ring of six Holocene pyroclastic cones occupies the caldera floor. These have been the source of a dozen trachytic pumice-fall deposits erupted during the past 5000 years. Sete Cidades is one of the most active Azorean volcanoes. Historical eruptions date back to the 15th century and have occurred from within the caldera and from submarine vents off the west coast.

References

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography.

Booth B, Croasdale R, Walker G P L, 1978. A quantitative study of five thousand years of volcanism on Sao Miguel, Azores. Phil Trans Roy Soc London, Ser A, 288: 271-319.

Martins J A, 1982. Excursion guide for field trip V1, Island of Sao Miguel. Proc Internatl Symp Activity Oceanic Volc, Archipelago Univ Azores, 3: 315-328.

Moore R B, 1983. Preliminary geologic map of Sete Cidades volcano, Sao Miguel, Azores (1:18,000). U S Geol Surv Open-File Rpt, 83-742.

Moore R B, 1990. Volcanic geology and eruption frequency, Sao Miguel, Azores. Bull Volcanol, 52: 602-614.

Moore R B, 1991. Geologic map of Sao Miguel, Azores. U S Geol Surv Map, I-2007.

Neumann van Padang M, Richards A F, Machado F, Bravo T, Baker P E, Le Maitre R W, 1967. Atlantic Ocean. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 21: 1-128.

Newhall C G, Dzurisin D, 1988. Historical unrest at large calderas of the world. U S Geol Surv Bull, 1855: 1108 p, 2 vol.

Zbyszewski G, Moitinho de Almeida F, Veiga Ferreira O da, Torre de Assuncao C, 1958. Geologic map of Sao Miguel (Azores). Servicos Geologicos Portugal, two 1:50,000 scale maps with 22 and 37 p texts (in Portuguese).

Eruptive History

There is data available for 16 Holocene eruptive periods.

Start Date	Stop Date	Eruption Certainty	VEI	Evidence	Activity Area or Unit
1880	Unknown	Confirmed	0	Unknown	Volcano Uncertain: submarine vent off Sao Miguel
1861	Unknown	Confirmed	0	Unknown	Volcano Uncertain: submarine vent off Sao Miguel
1811 Jun 14	1811 Jun 22	Confirmed	3	Historical Observations	Submarine vent west of Sete Cidades
1811 Feb 1	1811 Feb 8	Confirmed	2	Historical Observations	Submarine vent west of Sete Cidades
1713	Unknown	Confirmed	2	Historical Observations	West flank (Pico das Camarinhas)
1682 Dec 13	Unknown	Confirmed	2	Historical Observations	Submarine vent west of Sete Cidades
1638 Jul 3	1638 Jul 28	Confirmed	2	Historical Observations	Submarine vent west of Sete Cidades
1444 (?)	Unknown	Confirmed	4	Historical Observations	SW side of caldera (Caldeira Seca)
1110 ± 50 years	Unknown	Confirmed	2	Radiocarbon (uncorrected)	West flank (Ponta de Ferraria)
0950 ± 100 years	Unknown	Confirmed	2	Radiocarbon (uncorrected)	SE flank (Ferraria)
0670 ± 150 years	Unknown	Confirmed	3	Radiocarbon (uncorrected)	SE flank (Carvao)
0380 ± 300 years	Unknown	Confirmed	4	Tephrochronology	SE caldera floor (Lagoa Rasa)
0090 ± 100 years	Unknown	Confirmed	4	Radiocarbon (uncorrected)	SE caldera floor (Lagoa de Santiago)
0750 BCE ± 300 years	Unknown	Confirmed		Radiocarbon (uncorrected)	SE flank (Eguas)
2050 BCE ± 1000 years	Unknown	Confirmed		Tephrochronology	Caldeira do Alfreres and NW flank
3050 BCE (?)	Unknown	Confirmed	4	Tephrochronology	Seara Cerrado da Ladeira

Deformation History

There is no Deformation History data available for Sete Cidades.

Emission History

There is no Emissions History data available for Sete Cidades.

Photo Gallery

Both Lagoa Verde (Green Lake) in the foreground and Lagoa Azul (Blue Lake) appear blue in color in this view from the southern rim of the 5-km-wide summit caldera of Sete Cidades volcano on Sao Miguel Island. A nearly circular ring of six Holocene pyroclastic cones occupies the caldera floor. Sete Cidades is one of the most active Azorean volcanoes. Historical eruptions date back to the 15th century and have occurred from within the caldera and from submarine vents off the west coast.

Photo by Rick Wunderman (Smithsonian Institution).

A nearly circular ring of six Holocene pyroclastic cones occupies the floor of 5-km-wide Sete Cidades caldera. These have been the source of a dozen trachytic pumice-fall deposits erupted during the past 5000 years. Three of these forested cones appear in this view from the southern caldera rim, Caldeira Seca (extreme left), Caldeira do Alferes (left-center), and Seara (right center). The cones were constructed on the caldera floor adjacent to the two lakes of Lagoa Azul (top right) and Lagoa Verde (bottom right).

Photo by Rick Wunderman, 1997 (Smithsonian Institution).

The Caldeira Seca pumice ring (center) was formed during a 15th-century explosive eruption through the Sete Cidades caldera lake. A 1444 date is considered the most likely, although dates of 1439 and 1440 are sometimes listed. The Sete L tephra deposit originated from the 600-m-wide, 100-m-deep pumice ring, which is located on the SW floor of the Sete Cidades caldera, whose NE wall forms the horizon.

Photo by Rick Wunderman, 1997 (Smithsonian Institution).

The SE floor of Sete Cidades caldera contains a large trachytic lava dome that is cut by two lake-filled craters. The rim of Lagoa de Santiago crater is visible at the center, to the right of the Lagoa Azul and Lagoa Verde lakes occupying the caldera floor. The Lagoa Rasa crater rim appears at the extreme right, below the rim of Sete Cidades caldera. Lagoa de Santiago was the source of a major explosive eruption about 1900 years ago, and Lagoa Rasa erupted several centuries later.

Photo by Rick Wunderman, 1997 (Smithsonian Institution).

Caldeira do Alferes (center) is one of a group of six pyroclastic cones constructed on the floor of Sete Cidades caldera. The adjacent cone of Seara appears to the right of Caldeira do Alferes in this view from the western caldera rim. Strong eruptions of trachytic pumice occurred a dozen times during the past 5000 years from Sete Cidades, one of the most active volcanoes of the Azores.

Photo by Rick Wunderman, 1997 (Smithsonian Institution).

A small peninsula juts into Lagoa Azul ("Blue Lake"), one of two lakes partially filling the summit caldera on Sete Cidades volcano at the western end of Sao Miguel Island. The 5-km-wide caldera was formed about 22,000 years ago, and at least 22 post-caldera eruptions have occurred. This view looks to the NW from the rim of a post-caldera cone, Caldiera Grande. Two other post-caldera cones, Caldiera do Alfreres and Seara Cerrado da Ladeira, lie across the lake, behind and to the right of the town of Sete Cidades.

Photo by R.V. Fisher, 1980 (University of California Santa Barbara).

Smithsonian Sample Collections Database

There are no samples for Sete Cidades in the Smithsonian's NMNH Department of Mineral Sciences Rock and Ore collection.

Affiliated Sites

DECADE Data

The DECADE portal, still in the developmental stage, serves as an example of the proposed interoperability between The Smithsonian Institution's Global Volcanism Program, the MAGA Database, and the EarthChem Geochemical Portal. The Deep Earth Carbon Degassing (DECADE) initiative seeks to use new and established technologies to determine accurate global fluxes of volcanic CO₂ to the atmosphere, but installing CO₂ monitoring networks on 20 of the world's 150 most actively degassing volcanoes. The group uses related laboratory-based studies (direct gas sampling and analysis, melt inclusions) to provide new data for direct degassing of deep earth carbon to the atmosphere.

WOVOdat
   Single Volcano View
   Temporal Evolution of Unrest
   Side by Side Volcanoes

WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.

Large Eruptions of Sete Cidades

Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).

MIROVA

Middle InfraRed Observation of Volcanic Activity (MIROVA) is a near real time volcanic hot-spot detection system based on the analysis of MODIS (Moderate Resolution Imaging Spectroradiometer) data. In particular, MIROVA uses the Middle InfraRed Radiation (MIR), measured over target volcanoes, in order to detect, locate and measure the heat radiation sourced from volcanic activity.

MODVOLC Thermal Alerts

Using infrared satellite Moderate Resolution Imaging Spectroradiometer (MODIS) data, scientists at the Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, developed an automated system called MODVOLC to map thermal hot-spots in near real time. For each MODIS image, the algorithm automatically scans each 1 km pixel within it to check for high-temperature hot-spots. When one is found the date, time, location, and intensity are recorded. MODIS looks at every square km of the Earth every 48 hours, once during the day and once during the night, and the presence of two MODIS sensors in space allows at least four hot-spot observations every two days. Each day updated global maps are compiled to display the locations of all hot spots detected in the previous 24 hours. There is a drop-down list with volcano names which allow users to 'zoom-in' and examine the distribution of hot-spots at a variety of spatial scales.

EarthChem

EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).