Marapi an active West-Central Sumatra Volcano: a geological and petrological study

Marapi volcano (West - Central Sumatra), Sumatra’s most active volcano (not to be confused with Merapi on Java), located in a densely populated area and where more than 50 explosive eruptions have been recorded in the last 200 years has been studied in detail in the field to gain fundamental understanding of the volcano's activity in terms of its basic geology, petrology and geochemistry. Marapi is one of a few active volcanoes among many dormant volcanoes of this island. Large deposits of the nearby Maninjau caldera, dated 50 ka (n=3), associated with very silica-rich volcanic products is another reason for concern, since caldera formation is linked with severe explosive activity. Those deposits are found at the base of the volcano and largely in the deeply incised valley which follows the Sumatra fault extending parallel to the Sumatra volcanic front. A possible landslide parallel to the Sumatra fault is recognized on the LANDSAT image. Landslides on the external old external side have allowed the collection of the oldest part of the volcano as most of it is covered with a thick primary forest. These landslides occurring on old volcanic terrain are a threat to the surrounding population living nearby the rivers especially during the heavy rainy seasons. A 20 m high stratigraphic column has been studied, with the volcano’s explosive nature seen in the collected samples (i.e. bombs and pumices). A new sketch map of the area of the craters (6 over 2km) replaces the one made in 1921 at the Dutch colonial time. A geological and hazard map have been created showing the extension of the various deposits.