A'a Lava Flow, Hawaii
A'a lava flows are typically blocky, usually approximately 3-20 meters (10 to 66 feet) thick, and rolls over itself across the ground like a tank track. The jagged flow front normally creeps forward and steepens until a section becomes unstable and breaks off, revealing the incandescent central core. This flow is about 4 meters (13 feet) thick.

Pahoehoe Lava Flow, Kilauea Volcano Hawaii
Pahoehoe is a Hawaiian term 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. Pahoehoe flows are much thinner than a'a flows, sometimes being only 30-50 centimeters (12 -20 inches) thick. (Courtesy of J.D. Griggs, USGS)

Pahoehoe Lava Flow, Hawaii
The classic "ropy" texture of a pahoehoe lava flow is shown here. Scale bars is marked in 5-centimeter (2-inch) increments. (Courtesy of P. Mouginis-Mark, LPI)

'A'a Lava Channel, Hawaii
Lava pours down a well-developed lava channel near a series of erupting vents on the northeast rift zone of Mauna Loa Volcano. The eruption started from fissures in the volcano's summit caldera on March 25 and migrated to these vents on March 26. This lava channel fed an `a`a flow that traveled 25 kilometers until lava broke from the channel to feed another flow on March 29. The channel width varied 20 to 50 meters and extended to within 1 to 2 kilometers of the flow front. Channelized flows can also be found within lunar, Martian, and Venusian lava flows and are thought to be an indicator of high discharge rates.

Thurston Lava Tube, Hawaii
In Hawaii, many lava flows form tubes that may extend for several kilometers. This is an efficient way for the lava to travel comparatively large distances without significant cooling. Thurston Lava Tube, located close to the summit of Kilauea Caldera, is a fine example of this type of landform. Here the tube is approximately 3 meters (10 feet) in diameter. Note two lava benches on the wall on the left.

Fire Fountain Eruption, Pu'u O'o, Hawaii
Scientists studied fire fountains from the phase 34 eruption (August 1984) of Pu'u O'o in Hawaii to investigate the dispersal and cooling of ejected materials. In this view, the incandescent part of the plume is approximately 200 meters (660 feet) high. Large clasts from this fire fountain retained their heat to such an extent that they coalesced on the ground to form a lava flow that moved away from the vent (at right in this view). Pu'u O'o is located about 15 kilometers (9.3 miles) down rift from the summit of Kilauea Caldera, on the East Rift Zone.

Channels on Koko Crater, Oahu, Hawaii
The flanks of Koko Crater on the island of Oahu, Hawaii, show signs of extensive gully erosion. Koko Crater is approximately 400 meters (1,320 feet) high. Here we see valleys 3-5 meters (10-16 feet) deep that have been caused primarily by surface water flow and, close to the summit, by sapping. Although spaced further apart on Martian volcanoes such as Tyrrhena Patera, similar valleys might have formed on the older volcanoes on Mars as water from the original explosive eruptions was released at the surface. Note, however, that the valleys on Tyrrhena Patera might be 3-5 kilometers (1.9-3 miles) wide, which is wider than the entire Koko Crater cone.

Kupaianah Lava Lake, Hawaii
Using a spectroradiometer, scientists were able to measure the radiative temperature and thermal output from the Kupaianaha Lava Lake. This instrument collects spectra from 0.4-3.0 micrometers in over 800 channels, thereby permitting an accurate determination of the blackbody temperature of the surface. Such studies are of value because they show that the surface of a lava lake (or a lava flow) is remarkably cool - perhaps only a few hundred degrees centigrade - compared to the eruptive temperature of approximately 1,150°C (2,102°F). Such temperatures are quite similar to those the Voyager 1 spacecraft measured for the volcanic activity on Io, suggesting that silicate lavas, as opposed to molten sulfer, could exist within lava lakes on Io.

Kilauea Volcano, Hawaii
This is a color composite radar image of the Kilauea volcano on the Big Island of Hawaii. The city of Hilo can be seen at the top. The image shows the different types of lava flows around the crater Pu'u O'o. Ash deposits which erupted in 1790 from the summit of Kilauea volcano show up as dark in this image, and fine details associated with lava flows which erupted in 1919 and 1974 can be seen to the south of the summit in an area called the Ka'u Desert. In addition, the other historic lava flows created in 1881 and 1984 from Mauna Loa volcano (out of view to the left of this image) can be easily seen despite the fact that the surrounding area is covered by forest. The Kilauea volcano has been almost continuously active for more than the last 11 years. A moving lava flow about 200 meters (660 feet) in length was observed at the time of the shuttle overflight.

Mauna Loa Volcano, Hawaii
This image of the Mauna Loa volcano on the Big Island of Hawaii shows the capability of imaging radar to map lava flows and other volcanic structures. Mauna Loa has erupted more than 35 times since the island was first visited by westerners in the early 1800s. The large summit crater, called Mokuaweoweo Caldera, is clearly visible near the center of the image. Leading away from the caldera (towards top right and lower center) are the two main rift zones shown here in orange. Rift zones are areas of weakness within the upper part of the volcano that are often ripped open as new magma (molten rock) approaches the surface at the start of an eruption. The most recent eruption of Mauna Loa was in March and April 1984, when segments of the northeast rift zones were active. If the height of the volcano was measured from its base on the ocean floor instead of from sea level, Mauna Loa would be the tallest mountain on Earth. Its peak (center of the image) rises more than 8 kilometers (5 miles) above the ocean floor. The South Kona District, known for cultivation of macadamia nuts and coffee, can be seen in the lower left as white and blue areas along the coast. North is toward the upper left. The area shown is 41.5 by 75 kilometers (25.7 by 46.5 miles), centered at 19.5 degrees north latitude and 155.6 degrees west longitude. The different color combinations in this radar image are caused by differences in surface roughness of the lava flows. Smoother pahoehoe flows are depicted in red, and rougher a'a flows are shown in yellow and white.

Mauna Kea Summit, Hawaii
The Landsat Thematic Mapper (TM) obtains data of volcanoes on Earth in six spectral bands between 0.4 and 2.4 micrometers at 30-meters/pixel resolution, and one band between 8 and 12 meters at 100 meters/pixel. Here, TM data allows iron oxides (shown in red) in the cinder cones of Mauna Kea to be identified. Also visible in blue is the distribution of debris generated during the last ice age, which shows that Mauna Kea has not been active for several thousand years. North is at the top.

Vent Area, Kilauea, Hawaii
The December 1974 lava flow erupted from a series of en echelon fissures close to the summit of Kilauea Caldera. Here is an example of a fissure approximately 2 meters (6.6 feet) wide. Fissures of comparable dimensions may also have been the vents for the flows on the flanks of Sif Mons, Venus.

Pu`u ka Pele Cinder Cone, Mauna Kea Volcano
A cinder cone is a steep, conical hill of volcanic fragments that accumulate around and downwind from a vent. The rock fragments, often called cinders or scoria, are glassy and contain numerous gas bubbles "frozen" into place as magma exploded into the air and then cooled quickly. Cinder cones range in size from tens to hundreds of meters tall.