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Volcanoes of the Galapagos Islands
 Lava
flows are streams of molten rock that pour onto the Earth's surface from an
erupting vent. Both moving lava and the resulting solidified deposit are
referred to as lava flows. Lava flows come in a variety of shapes and sizes.
They are impacted by the wide range in speeds of the different lava types
(basalt, andesite, dacite, and rhyolite), the lava discharge during
eruptions, and the characteristics of the erupting vent and topography over
which lava travels. Fluid basalt flows like those in the
Galapagos can
extend tens of kilometers from an erupting vent. The leading edges of basalt
flows can be as fast as 6 miles (10 km) per hour on steep slopes but they
typically travel less than 1/2 mile (1 km) per hour on gentle slopes. When
basalt lava flows are confined within a channel or lava tube on a steep
slope, the main body of the flow reaches speeds more than 18 miles (30 km)
per hour.
Lava, the material expelled from the volcanoes is present
in the Galapagos and takes a variety of forms. On Santiago it is possible to
see 2 distinct types of lava patterns. Pahoehoe is a Hawaiian name for
basaltic lava that has a smooth, hummocky, or ropy surface. A pahoehoe flow
typically advances as a series of small lobes and toes that continually
break out from a cooled crust. The surface texture of pahoehoe flows varies
widely, displaying all kinds of bizarre shapes often referred to as lava
sculpture.
The incredibly spiny surface of a solidified Lava flow
makes walking very difficult and slow. The clinkery surface actually covers
a massive dense core, which is the most active part of the flow. As pasty
lava in the core travels down slope, the clinkers are carried along at the
surface. At the leading edge of an lava flow, however, these cooled
fragments tumble down the steep front and are buried by the advancing flow.
This produces a layer of lava fragments both at the bottom and top of an
lava flow.
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Tuff Cones Pinnacle Rock on
Bartolome has
become one of the most photographed sights in the islands. The Tuff Cone is
a vertical rock formation created by the consolidation of hardened ash.
During the eruption hot lava reached the sea causing an explosion. Particles
splattered down in the shape of cone often known as a Tuff Cone or Cinder
Cone.
Lava Tubes
Exploring the Lava Tubes in the highlands of
Santa Cruz
makes an interesting and eerie adventure. These giant wormholes are caused
when the exterior portion of a pahoehoe lava flow hardens while the interior
lava continues to flow. Eventually the lava flow diminishes and there is not
enoughfumaroles courtesy of the USGS lava left to fill the hollow tube.
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Calderas & Fumaroles
 A
caldera is a large, usually circular depression at the summit of a volcano
formed when magma is withdrawn or erupted from a shallow underground magma
reservoir. The removal of large volumes of magma may result in loss of
structural support for the overlying rock, thereby leading to collapse of
the ground and formation of a large depression. Calderas are different from
craters, which are smaller, circular depressions created primarily by
explosive excavation of rock during eruptions. Of the many specific geologic features of interest in the
Galapagos,
Isabela is the only island in the chain created by the merging of 6
volcanoes. A 3 to 4 hour hike up the island takes visitors to one of the
largest calderas in the world at 6 x 5 miles (10 x 8 km) on Sierra Negra and
to see the Fumaroles or “steam valves” being released from the active
crater.
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