page_title: Hualālai
section_title: Structural features
hierarchical_section_title: Hualālai / Geology / Structural features
caption_attribution_description: English: This image was taken during exploration of an open vertical volcanic conduit on Hualalai Volcano in Hawaii. It is in the floor of a volcanic vent known as Puhia Pelee
context_page_description: Hualālai is an active volcano on the island of Hawaiʻi in the Hawaiian Islands. It is the westernmost, third-youngest and the third-most active of the five volcanoes that form the island of Hawaiʻi, following Kīlauea and the much larger Mauna Loa. Its peak stands 8,271 feet above sea level. Hualālai is estimated to have risen above sea level about 300,000 years ago. Despite maintaining a very low level of activity since its last eruption in 1801, and being unusually inactive for the last 2,000 years, Hualālai is still considered active, and is expected to erupt again some time within the next century. The relative unpreparedness of the residents in the area caused by the lull in activity would worsen the consequences of such an event.
  The area near the volcano has been inhabited for centuries by Hawaiian natives, dating back to before recorded history. The coast west of Hualālai in particular had several royal complexes. The volcano is also important ecologically, is home to many rare species and several nature reserves near the summit, and is a popular hiking attraction.
context_section_description: Hualālai stands at 8,271 ft (2,521 m) with a prominence of 3,071 ft (936 m). It is the westernmost of the five major volcanoes which form the island of Hawaiʻi. Being in the post-shield stage of development, Hualālai is overall much rougher in shape and structure than the more youthful Mauna Loa and Kīlauea. Hualālai's structure is denoted by three rift zones: a well-developed one approximately 50° to the northwest, a moderately developed one to the southeast, and a poorly developed one trending northwards about 3 mi (5 km) east of the summit. There are over 100 cinder and spatter cones arranged along these rift zones. Hualālai has no summit caldera, although there is a collapse crater about 0.3 mi (0.48 km) across atop a small lava shield. Much of the southern slope (above the modern town of Kailua-Kona) consists of lava flows covered by a layer of volcanic ash from 10 to 100 cm (4 to 39 in) thick. In comparison with the other volcanoes of the island of Hawaiʻi, it is the third-tallest, third-youngest, third-most active, and second-smallest, making up just 7% of the island.
  A major subfeature of Hualālai is Puʻu Waʻawaʻa, Hawaiian for "many-furrowed hill", a volcanic cone standing 372 m (1,220 ft) tall and measuring over 1.6 km (1 mi) in diameter. It extends for 9 km (6 mi), and has a prominence of 275 m (902 ft), north of the summit at 19°46′15″N 155°49′56″W. The cone is constructed of trachyte, a type of volcanic lava that exists at no other volcano on Hawaiʻi. Trachyte flows move more slowly than the typically "runny" Hawaiian lavas, a characteristic caused by its high (over 62%) silica composition (typical basalt is only 50% silica). Geologists hypothesize that Puʻu Waʻawaʻa originally formed during a pumice eruption a little over 100,000 years ago, and has continued to build itself since then, with at least three distinct trachyte flows recognized. The eruptions, although partially covered by flows from Hualālai and Mauna Loa, have built a distinctive structure known as the Puʻu Anahulu ridge.
  The westward-facing flank of Hualālai forms a large underwater slump known as the North Kona slump. An area of about 1,000 km² (390 sq mi), the slump consists of an intricate formation of beaches and scarps 2,000 to 4,500 m (6,600 to 14,800 ft) below the waterline. This area was explored more closely in a 2001 joint Japan-United States project to explore the volcano's flanks, utilizing the remotely operated vehicle ROV Kaikō. Data collected showed that the lava flows there originated in shallow water 500 to 1,000 m (1,600 to 3,300 ft) deep, and that unlike similar slumps at other volcanoes, the slump at Hualālai formed gradually.
  Hualālai is a known source for xenoliths, rock from the Earth's mantle that have been brought up in lava flows. Many prehistoric deposits, as well as those from the 1801 event, contain xenoliths of large size and abundant quantity.
caption: An expedition down a lava conduit in Hualālai volcano
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