Kozushima

Photo of this volcano
  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 34.219°N
  • 139.153°E

  • 572 m
    1876 ft

  • 284030
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number

Most Recent Bulletin Report: October 1995 (BGVN 20:10) Citation IconCite this Report


Earthquake swarm ends in mid-October

As reported in BGVN 20:09, on 6 October a M 5.6 earthquake occurred adjacent to Kozu-shima and a seismic swarm followed for the next few days. After that, seismic events continued but decreased toward the end of October; in total, during October there were 246 felt earthquakes.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.

The Global Volcanism Program has no Weekly Reports available for Kozushima.

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.

04/1991 (BGVN 16:04) Earthquake swarm but no surface activity

10/1991 (BGVN 16:10) Earthquake swarm N of island

01/1992 (BGVN 17:01) Earthquake swarm follows nearby Nii-jima seismicity; no surface activity observed

04/1992 (BGVN 17:04) Two seismic swarms; no surface changes evident

05/1992 (BGVN 17:05) Continued seismic swarms

06/1992 (BGVN 17:06) Earthquake and aftershocks

08/1992 (BGVN 17:08) Weak seismic swarm; surface activity unchanged

09/1992 (BGVN 17:09) Weak earthquake swarm

10/1992 (BGVN 17:10) Earthquake swarm but no surface changes evident

03/1993 (BGVN 18:03) Earthquake swarm on 25 March; no surface anomalies

08/1993 (BGVN 18:08) Earthquake swarms

09/1995 (BGVN 20:09) Strong earthquake swarm in early October

10/1995 (BGVN 20:10) Earthquake swarm ends in mid-October




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


April 1991 (BGVN 16:04) Citation IconCite this Report


Earthquake swarm but no surface activity

An earthquake swarm (M <= 4.0) occurred from 2100 to 2400 on 23 April, with seismicity gradually returning to normal levels by the following day. Many of the earthquakes were felt by residents (to JMA intensity IV). Swarm events were centered from the W coast to 20 km SW of the island (figure 1), at 0-10 km depth. No surface activity was reported.

Figure (see Caption) Figure 1. Epicenter map (top) and space/time diagram (bottom) showing seismicity around Kozu-shima and Nii-jima volcanoes, January 1991-June 1992. Courtesy of JMA.

Information Contacts: JMA.


October 1991 (BGVN 16:10) Citation IconCite this Report


Earthquake swarm N of island

An earthquake swarm occurred 24-25 October in the sea 7 km N of Kozu-shima (figure 1). The largest shocks (M 4.9) were recorded at 1746 and 1754 on the 24th. Changes in surface activity were not observed on the island or in the epicentral area. The seismicity was the first for the area since 23 April . . . .

Information Contacts: JMA.


January 1992 (BGVN 17:01) Citation IconCite this Report


Earthquake swarm follows nearby Nii-jima seismicity; no surface activity observed

On 26-27 January, three weeks after an earthquake swarm centered ~10 km NE of the volcano, another swarm was recorded a few kilometers E of Kozu-shima (figure 1). The 26-27 January swarm's two largest shocks, M 3.3, occurred at 2041 and 2050 on the 26th. No surface activity was observed.

Information Contacts: JMA.


April 1992 (BGVN 17:04) Citation IconCite this Report


Two seismic swarms; no surface changes evident

A seismic swarm occurred 21-25 April, centered a few kilometers NW of the island. Some of the shocks were felt by island residents; the largest, M 3.6, occurred on 23 April. Another swarm was recorded on 8 May, centered E of the island (maximum M 3.9). No surface anomalies were observed.

Information Contacts: JMA.


May 1992 (BGVN 17:05) Citation IconCite this Report


Continued seismic swarms

Abnormal seismicity continued around the volcano in May, when 2 earthquake swarms were recorded. On 8 May a swarm occurred 2-3 km E of the island, with M <3.9. The second, on 14-16 May, occurred 3-4 km NW, with the largest event (M 4.9) recorded at 0731 on 15 May. No surface anomalies were observed.

Information Contacts: JMA.


June 1992 (BGVN 17:06) Citation IconCite this Report


Earthquake and aftershocks

A M 5.2 earthquake, centered in the sea 8 km SW of the volcano at 9 km depth, occurred on 15 June at 1046. Island residents felt the shock at intensity 5 on the JMA scale of 0-7. Data from 30 stations of the Worldwide Standardized Seismic Network yielded magnitudes of 4.9 (mb) and 4.7 (Ms). One person was slightly injured by a rockfall, and wallrock collapse at 10 sites closed 5 roads to traffic. Aftershocks continued until 17 June off the island's SW coast. The event was the second largest since . . . April 1991 (figure 1). No surface anomalies were observed on the island or on the sea-surface nearby.

Information Contacts: JMA; NEIC.


August 1992 (BGVN 17:08) Citation IconCite this Report


Weak seismic swarm; surface activity unchanged

A weak earthquake swarm was detected 5 km NE of the volcano island on 18 August. Maximum magnitude was 3.0. No surface activity was evident on the island or in the sea.

Information Contacts: JMA.


September 1992 (BGVN 17:09) Citation IconCite this Report


Weak earthquake swarm

A weak earthquake swarm occurred 5 km W of the island on 1 September. Maximum magnitude was 2.1. No surface activity was evident on the island or in the sea.

Information Contacts: JMA.


October 1992 (BGVN 17:10) Citation IconCite this Report


Earthquake swarm but no surface changes evident

A swarm of earthquakes occurred midway between [Nii-jima and Kozu-shima] islands 17-20 October. The largest earthquake was M 5.1, at 2237 on 17 October. No ocean-surface anomalies were observed.

Information Contacts: JMA.


March 1993 (BGVN 18:03) Citation IconCite this Report


Earthquake swarm on 25 March; no surface anomalies

. . . On 25 March, a swarm occurred at Kozu-shima island, ~20 km SW of Nii-jima. The largest event was M 3.9. No surface anomalies, onshore or offshore, were observed . . . .

Information Contacts: JMA.


August 1993 (BGVN 18:08) Citation IconCite this Report


Earthquake swarms

An earthquake swarm near and below Kozu-shima island occurred on 9-10 August, with 12 shocks felt on the island, the largest M 3.3. Another earthquake near the island, M 3.7, occurred in the early morning on 22 August.

Information Contacts: JMA.


September 1995 (BGVN 20:09) Citation IconCite this Report


Strong earthquake swarm in early October

At 2143 on 6 October, a M 5.6 earthquake occurred near Kozu-shima (figure 2). The earthquake, which had an intensity at Kozu-shima of V on JMA's scale, caused a few landslides there. A M 4.8 earthquake 14 minutes earlier had an intensity of IV. During the next several days, an earthquake swarm continued offshore to the SW of Kozu-shima (figure 2, bottom). The swarm's maximum depth shifted downward with time, reaching 20-25 km. None of this seismicity was thought to have been induced by volcanism.

Figure (see Caption) Figure 2. Kozu-shima epicenter map (top) and plot of focal depths versus time for September through 16 October 1995 (bottom). Courtesy of JMA.

Though obscured by epicenters on figure 2, Kozu-shima island has dimensions of 4 x 6 km and lies 20 km SSW of Nii-jima island and adjacent to the Izu Peninsula. Kozu-shima contains abundant rhyolitic surge deposits and lava domes. Its last eruption was in 838-840 AD. Seismicity near the volcano, and sometimes in vicinity of Nii-jima, has been episodically high in recent years.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.


October 1995 (BGVN 20:10) Citation IconCite this Report


Earthquake swarm ends in mid-October

As reported in BGVN 20:09, on 6 October a M 5.6 earthquake occurred adjacent to Kozu-shima and a seismic swarm followed for the next few days. After that, seismic events continued but decreased toward the end of October; in total, during October there were 246 felt earthquakes.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.

Eruptive History


Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).


Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
0838 Aug 2 (?) Unknown Confirmed 4 Historical Observations Tenjo-san
[ 0832 ] [ Unknown ] Uncertain    
0100 BCE ± 950 years Unknown Confirmed   Hydration Rind NW tip of island (Kobe-yama)
0750 BCE ± 700 years Unknown Confirmed   Hydration Rind N tip of island (Anano-yama, Hanatabe)
8050 BCE (?) Unknown Confirmed   Tephrochronology Jogo-yama

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.

Photo Gallery


Tenjo lava dome, in the central part of the island of Kozu-shima, was formed during the most recent eruption of the volcano in 838 CE. Formation of the rhyolitic lava dome was accompanied by pyroclastic flows and surges and the extrusion of flow-banded lava flows.

Photo by Ichio Moriya (Kanazawa University).
See title for photo information.
The cultivated floor of an explosion crater (left) and a flat-topped lava dome (right) are part of Kozu-shima volcano in the northern Izu Islands. The small 4 x 6 km island is formed by a cluster of rhyolitic lava domes and associated pyroclastic deposits. The youngest and largest dome, 574-m-high Tenjo-yama, occupies the central portion of the island. Most of the older domes flank Tenjo-yama on the north. Only two historical eruptions, from the 9th century, are known.

Photo by Ichio Moriya (Kanazawa University).
See title for photo information.

Smithsonian Sample Collections Database


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

Affiliated Sites