5. Scoria (cinder) cones Dan Barker March 2009 Scoria cone, Mauna Kea, HI In volcanology, scoria is the term used for vesicular angular to subrounded fragments of lava, more dense than pumice and darker. It is produced by some lava fountains and mild explosions, and is usually basalt to andesite in composition. Outside the earth sciences, scoria is the Greek word for excrement. Scoria, summit of Vesuvius, Italy. Fresh scoria, Kilauea caldera This is more typical scoria, lightly stuck together by secondary minerals. Rapa Nui (Easter Island) Scoria or cinder cones are the most numerous volcanic landforms above sea level. They may occur in clusters without any other volcanoes, or on the flanks of larger shield volcanoes or stratovolcanoes, or within calderas. Scoria cones represent relatively brief eruptions (days to a few years). Eruptive activity then does not recur at the same spot, but may start a kilometer (more or less) from the earlier cone. Usually they contain a central crater over the vent, and have inner and outer slopes up to 32 degrees before erosion begins to destroy them. Because they are accumulations of fragments that were already solid when they landed, many are easily excavated by nature and by humans. We know a lot more about the internal structure of scoria cones than other volcanoes because many have been quarried; scoria are usually loose and can easily be sorted into different sizes, so they are good road and construction materials. Many scoria cones are sources of lava flows, commonly of greater volume than the cone itself. The lava almost always issues from the base of the cone, not from the top crater. This allows the lava to avoid climbing higher in the conduit. Because scoria are less dense than lava, the lava flow burrows under the cone and escapes. Parts of the scoria cone may be torn away and rafted on top of the lava. SP Crater in Arizona is a classic example of a scoria cone and associated lava flow. Other examples of cones and associated lava flows are in the next 10 images. Scoria cone and lava flows, east flank of Fogo volcano, Cape Verdes Belknap Crater and lava flows, McKenzie Pass, OR. The vegetated "islands" that were not buried by lava are called kipukas, one of many Hawaiian words in volcanology. Sunset Crater, AZ, with lava flow in the foreground. Lava flow from base of scoria cone, Lava Butte, OR Scoria cone and collapsed lava tube, Medicine Lake Volcano, CA Lava tube Scoria cone The 1973 scoria cone of Eldfell (Fire Mountain), Heimaey,Iceland 1973 scoria cone (Eldfell)and its lava flow in the foreground. Heimaey, Iceland. Rafted parts of scoria cone on 1973 lava from Eldfell, Heimaey, Iceland Rafted parts (arrows) of scoria cone, 1973 lava, Heimaey, Iceland Rafted scoria cone segments in lava flow, Craters of the Moon, ID The most notorious scoria cone is Monte Nuovo in the Campi Flegrei caldera on the western outskirts of Naples. It suddenly appeared in 1538 after a long prelude of earthquakes and land uplift. The uplift is well documented by court records, as many people claimed the new land exposed along the shore of the bay. After a few days, activity halted, so people climbed the New Mountain to look into the crater. Then the eruption resumed, killing about 24 people. Since 1538, there have been many episodes of earthquakes, uplift, and sinking of land, but no eruptions in the caldera yet. Monte Nuovo and Lake Averno, Campi Flegrei caldera, Italy Monte Nuovo from the south. The shoreline has risen and sunk repeatedly for at least 3000 years. If an urban or suburban area contains scoria cones, and the youngest is less than 10,000 years old, this is a Bad Sign, because activity in this volcanic field may not be over. Metropolitan areas containing young scoria cones include Auckland, NZ; Mexico City; Naples, Italy; Clermont- Ferrand, France; Albuquerque, NM; and Medina,Saudi Arabia. Auckland, New Zealand, and a few of its many young scoria cones (arrows). Scoria cones at Nicolosi, on the flank of Etna, Sicily Here are some other notable scoria cones, with significant features indicated. Ubehebe Crater north of Death Valley, CA Two scoria cones (and a lava dome hiding behind them) viewed from Puy de Dome west of Clermont- Ferrand, France. Capulin Mountain, NM (almost in TX) Scoria cone east of Guimar, Tenerife, Canary Islands. Like many other scoria cones, this one has its rim higher in one direction, because wind during eruption pushed scoria to one side. 1959 vent and Puu Puai scoria cone, Kilauea Iki, Hawaii. Prevailing wind was from behind the camera. Rootless spatter-fed flow (center) in Herchenberg scoria cone, Germany During the last stages of some scoria cone eruptions, the magma has been depleted in gas so much that spatter (liquid blobs) are erupted instead of scoria (frothy chunks, solid when they land). Here at Sunset Crater, AZ, a spatter rim has formed (arrows). At the north end of the island of Vulcano, off the north coast of Sicily, there is an east-west row of three scoria cones. The oldest and easternmost, Vulcanello I, first appeared in 183 BC, and the other two built sequentially to the west. Here is a wave-cut section of Vulcanello I. This is the crater of Vulcanello III. Scoria cones on the southeast flank of Medicine Lake shield volcano, CA Scoria cone, Landmannalaugar, Iceland. The thick moss cover is comfortable to rest on! Black Butte on lower west flank of Shasta, CA. This is steeper and larger than most scoria cones. Quarried section of scoria cone, Atlacomulco, Mexico. An older crater rim is buried by younger scoria. Crater rim buried by younger scoria, Rockeskyller Kopf, Germany Scoria cone section, Rockeskyller Kopf,Germany Faults, down toward vent, Hasenberg, West Eifel, Germany Inverse grading of scoria (by rolling), Herchenberg, Germany. By the "Brazil nut effect" the larger particles concentrate at the top. Scoria cones, low on west flank of Mauna Kea, Hawaii