17/03/2014-23/03/2014
This week’s
volcano of the week is:
Rungwe
Location: Tanzania, East Africa
Type: Stratovolcano
Elevation: 2956 m, 9696 ft
Last
Eruption: 1250
Status: Dormant
Details:
Rungwe is a 2961 metre (9713 feet) stratovolcano located in
the northeast Mbeya region between latitude 9.13°S, longitude 33.67° E and is
the largest volcano found in this region with a caldera measuring approximately
two and a half miles in diameter. The formation of Rungwe caldera is unclear
and no strong evidence exists to indicate its formation process, however again
it is thought to have been caused by the magma support from beneath being
removed therefore causing the volcano to collapse. The Rungwe caldera varies in
elevation, having a thick cover of pumice on the caldera floor and the entire
west side of the caldera has been destroyed by an eruption. The caldera
consists of tuffs, pumice, lava and various other features such as tuffs,
explosive centres, pyroclastic cones and lava domes make up the other volcanic
features of Rungwe.
Tuffs are
concentrated mainly in the south and southeast of Rungwe and a large number of
explosion craters are located in the northwest of the volcano thought to have
been created during an ‘explosive’ phase of the volcano according to Harkin
(1960). Although the dates of the eruptions of Rungwe volcano are unknown and
estimated to be around the Holocene or Pleistocene age, evidence does exist to
show the extent and types of volcanic hazard that occurred during the eruptions.
Lava flows
exist over a large area on and around Rungwe including on the caldera floor and
walls, west and in the northwest, south (13 miles from source) region of Rungwe.
Some flows measure up to 100 feet in thickness such as the one found in the
west and most of the lava flows appear to be young.
Wide spread ash, pumice and lapilli exists on Rungwe and the surrounding countryside, some spreading to other volcanoes in the region such as Kieyo and Ngozi. The photo below shows evidence of Rungwe pumice beside a road which indicate the thickness of the pumice showers during an eruption. In the upper parts of Rungwe pumice measures up to 100 feet in thickness but decreasing in size and thickness further away. These pumice and ash showers which also occurred during the most recent eruption of Rungwe, along with lava flows were possibly controlled by the wind speed and direction on the day of the eruption.
Occasionally during very heavy rainfall in the region landslides are caused as a result of the thick covering of pumice and ash, however this is also limited due to the local drainage character and the forest cover. A landslide event that occurred in 1955 due to heavy rainfall (17 inches in one night) and the volcanic deposits of ash and pumice, caused great devastation in the region destroying property and killing people, although figures are unclear.
Wide spread ash, pumice and lapilli exists on Rungwe and the surrounding countryside, some spreading to other volcanoes in the region such as Kieyo and Ngozi. The photo below shows evidence of Rungwe pumice beside a road which indicate the thickness of the pumice showers during an eruption. In the upper parts of Rungwe pumice measures up to 100 feet in thickness but decreasing in size and thickness further away. These pumice and ash showers which also occurred during the most recent eruption of Rungwe, along with lava flows were possibly controlled by the wind speed and direction on the day of the eruption.
Occasionally during very heavy rainfall in the region landslides are caused as a result of the thick covering of pumice and ash, however this is also limited due to the local drainage character and the forest cover. A landslide event that occurred in 1955 due to heavy rainfall (17 inches in one night) and the volcanic deposits of ash and pumice, caused great devastation in the region destroying property and killing people, although figures are unclear.
The history of activity of Rungwe according to Harkin
(1960) can be summarized as follows although the dates of these events are
unknown;
• Formation of central volcano as a result of phonolitic
trachytes lava and tuffs erupting
• Eruption of basaltic lavas on the west and northwest of
Rungwe volcano
• Rungwe caldera formed, possibility of it having a crater
lake
• Explosive phase of the volcano creating
explosion craters and destroying the west wall of the caldera. Lahars produced
on the west side of the mountain as shown on figure 3.2.7 below
• Formation of cones, eruption of pumice and ash, lava
flows
According to the Global Volcanism Program the last eruption of Rungwe was
in the year 1250 (+/-40 years). Two other eruptions have been dated as shown in
the table below.
Start Date
|
Stop Date
|
Eruption Certainty
|
VEI
|
Evidence
|
Activity Area or Unit
|
1250 ± 40 years
|
Unknown
|
Confirmed
|
Radiocarbon (corrected)
|
Kizungu Tephra
|
|
0050 BCE ± 100 years
|
Unknown
|
Confirmed
|
4
|
Radiocarbon (corrected)
|
Isongole Pumice
|
2050 BCE (?)
|
Unknown
|
Confirmed
|
5
|
Tephrochronology
|
Rungwe Pumice
|
Landscape of lahar origin from Rungwe eruption found in the southwest of the volcano (Source: Harkin, 1960)
Evidence of pumice from Rungwe on a road cutting (Source: Harkin, 1960)
Lava flow direction (shown in arrows), lapilli, volcanic bombs, ash, pumice deposits and lava flows around Rungwe caldera, shown in shades of red (Source: Harkin, 1960)
No comments:
Post a Comment