[4] 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.

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.

[1] 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 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.

[5] 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.

Geologists hypothesize that Puʻu Waʻawaʻa originally formed during a pumice eruption a little over 100,000 years ago, and has continued to build 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.

[9] Geological mapping of Hualālai indicates that as much as 80% of its surface has been topped by lava flows during the last 5,000 years,[1] entirely composed of shield alkalic basalt.

[12] A recent calm period, with almost no earthquake or magmatic activity at Hualālai, has seen the growth of homes, businesses, and resorts on its flanks.

The most recent major activity at the volcano was in 1929, when an intense earthquake swarm rocked it, most likely caused by magmatic action near its peak.

This eruption produced very fluid alkalic basalt lava flows that entered the ocean off the western tip of Hawaiʻi island.

There is a local legend that after the failure of several offerings of animals and other items to the gods, the flow was finally stopped when Kamehameha I threw a lock of his own hair into the fire.

It is theorized that in the near past, Hualālai has been active around the same time as both Mauna Loa and Kilauea, although precise dating is impossible.

In addition, the Hawaiian Volcano Observatory uses GPS to measure slight changes in tilt and slope of Hualālai, indicative of magmatic movement.

[19] Although Hualālai does experience several magnitude-4 earthquakes per year, these are attributed to a deep source off the coast of the north-western rift zone and are not related to the movement of magma.

[20] The Kaloko-Honokōhau National Historical Park lies on the shore west of Hualālai, over the site of an ancient Hawaiian settlement.

Although it is called kekaha ʻaʻole wai (lands without water), the rugged volcanic terrain attracted much sea life, making it an appealing place to settle.

[22] Today, the coast west of Hualālai is a popular location for vacation resorts, since the rain shadow of the mountain causes many sunny days.

[27] The family of early coffee merchant Henry Nicholas Greenwell owned a large ranch on the western side of the volcano.

Many of the collapse craters in particular have vegetation, and a few even have respectably-sized "vertical forests" inside, including several eucalyptus tree groves.

[35][36] The Wai Aha spring reserve on the lower slopes of the mountain is somewhat swampy and is home to the flowering evergreen ōhiʻa (Metrosideros polymorpha), the woody climber ʻIeʻie (Freycinetia arborea), and a dense undergrowth of ʻAmaʻu (Sadleria cyatheoides).