A Hawaiian Volcano Observatory team uses a drilling rig to extract drill core from the cooling lava lake in Kilauea Iki crater. At the time of this 1968 project, nearly a decade after a lava lake filled Kilauea Iki during the 1959 eruption, the crust had solidified to a depth of about 30 m. The drill core reached down to 60 m without reaching the bottom of the still partially molten lava lake. This project, the first to use a drill rig to sample a lava lake, allowed study of vertical variations in chemistry, mineralogy, and temperature within a cooling lava lake.
Among the many monitoring techniques used by Hawaiian Volcano Observatory staff at Kilauea volcano is precision leveling. Millimeter-scale variations in the elevation of two fixed points can be detected with an optical-level instrument by measuring the precise difference in elevation on leveling rods placed above them. Slight inflation of a volcanic edifice commonly occurs prior to eruptions. Measurements such as these in 1968, with the Puu O'o cinder cone in the background, are one of several techniques used to help forecast eruptive events.
Large-volume lava flows are commonly fed through tubes beneath the crusted-over surface of the flow. The roofs of lava tubes frequently collapse, producing skylights, through which the flowing lava is visible. This October 21, 1970, photo of a lava flow from Mauna Ulu, at Hawaii's Kilauea volcano, shows several ledges within the lava tube that mark previous levels of flow. The walls and roofs of lava tubes are efficient thermal insulators that allow long-distance transport of lava. Some tubes during the Mauna Ulu eruption were 11 km long.
The inexorable forces of nature often bring human efforts to a halt. Lava flows from the current east rift zone eruption of Hawaii's Kilauea volcano frequently overran the coastal highway, enveloping traffic signs such as this one. Efforts to reconstruct the highway were eventually abandoned in the face of continued vigorous production of lava flows that reached the coast over a broad area.
Two types of lava flows, pahoehoe and aa, are different textural forms of otherwise identical lava. The smooth-textured pahoehoe lavas (left) are formed by stable upwelling of gas-poor lava, whereas the hackly-surfaced aa flows are produced during eruptions with high lava fountaining of gas-rich magma. Eruptions of aa lava commonly evolve into sustained production of pahoehoe. Because of differential weathering rates, the overlying pahoehoe flows look younger than the associated aa flows, and the two flows are easily mistaken for flows of greatly differing age.
Lava flows are produced when magma reaches the surface and is erupted non-explosively. Basaltic lava flows, such as this September 1979 flow from the east rift zone of Kilauea volcano, are Earth's most common volcanic product. Basaltic lava flows have initial temperatures of about 1200 degrees Centigrade and a high fluidity. The volume, velocity, and travel distance of lava flows is related to silica content. More silica-rich lava flows have lower temperatures, are usually thicker, much more viscous, and travel shorter distances.
An aa lava flow, with a characteristic hackly surface, advances across a smooth-textured pahoehoe lava flow. The front of this June 3, 1994, aa flow at Laeapuki, near the Puna coast of Kilauea volcano, is about 1 m high. Aa flows are produced by eruptions with high lava fountains of gas-rich magma. Eruptions producing aa lava commonly evolve into sustained eruptions of gas-poor pahoehoe.
The newly solidified surface of pahoehoe lava flows commonly has a silvery or irridescent color that is produced by recrystallization of volcanic glass as it becomes hydrated and oxidized. Pahoehoe lavas form during eruptions that are characterized by stable upwelling of gas-poor magma. This smooth-textured pahoehoe flow at Kilauea volcano was photographed in August 1994.