According to the
U.S. Census Bureau, the county has a total area of , of which is land and (20.8%) is water. The county's land area comprises 62.7 percent of the state's land area. It is the highest percentage by any county in the United States.
Delaware's
Sussex County comes in second at 48.0 percent, while
Rhode Island's
Providence County is third at 39.6 percent. At its greatest dimension, the island is across. Measured from its sea floor base to its highest peak,
Mauna Kea at is the world's tallest mountain, taller than even
Mount Everest, since the base of Mount Everest is above sea level. The most southern point of Hawaii,
Ka Lae, is the
southernmost point of the United States. The nearest landfall to the south is the
Line Islands. To the northwest of the island of Hawaii is the island of
Maui, whose
Haleakalā volcano is visible from HawaiKau, Hawaii|i Island across the
Alenuihāhā Channel.
Volcanism red lava enters the ocean. Three Waikupanaha and one Ki lava ocean entries. The island of Hawaii is built from five separate
shield volcanoes that erupted somewhat sequentially, one overlapping the other. These are (from oldest to youngest): •
Kohala – extinct •
Mauna Kea – dormant •
Hualālai – active •
Mauna Loa – active, partly within
Hawaii Volcanoes National Park •
Kīlauea – active, part of Hawaii Volcanoes National Park Geological evidence from exposures of old surfaces on the south and west flanks of Mauna Loa led to the proposal that two ancient volcanic shields (named Nīnole and Kulani) were all but buried by the younger Mauna Loa. Geologists now consider these "outcrops" to be part of Mauna Loa. Based on
geochemical (including
trace elements) and
isotope differences in their eruptive products, Hawaiian volcanoes fall into two families. The differences are believed due to their separate magma systems. Hualālai and Mauna Loa are members of one family, while Kohala, Mauna Kea, and Kilauea are members of the other. Because Mauna Loa and Kīlauea are active volcanoes, the island is growing. Between January 1983 and September 2002,
lava flows added to the island. Lava flowing from Kīlauea destroyed several towns, including
Kapoho in 1960 and again in 2018, and
Kalapana and
Kaimū in 1990. In 1987 lava filled in "Queen's Bath", a large, L-shaped, freshwater pool in the Kalapana area. Another 875 acres were added between May and July 2018 by the
2018 lower Puna eruption, with "Fissure 8" located within
Leilani Estates subdivision being a primary source of the lava.
Green Lake, the largest freshwater lake on the island, was covered by lava in that eruption as well as Ahalanui Beach Park and part of
Isaac Hale Beach Park, the latter of which was inundated with
black sand, rendering its
boatramp unusable. Mauna Loa erupted briefly in 2022, 38 years after the prior activity. Some geologists also count two
undersea volcanoes in the base of the island.
Māhukona off the northwest corner of the island has eroded below the ocean surface.
Kamaehuakanaloa (formerly Lōihi) is under water southeast of Hawaii. It is an erupting seamount that has grown to reach below the ocean surface, and it is forecast to break the surface in 10,000 to 100,000 years. The volcano Kilauea, has had its 38th eruption on December 8th 2025. It began Saturday morning and sent lava shooting at least 1,000 feet into the air, according to the USGS. At one point, a "rare" triple fountain occurred: three lava fountains spewed from vents in the north and south cones. During these events, the USGS put a code orange in place, which indicates that an eruption is either likely or occurring, but with no, or minor, ash. There was also a warning of tephra, or hot glassy volcanic fragments, as well as pumice, scoria and reticulite, which can fall on the ground within one to three miles of the eruptive vents.
Great Crack at
Hawaii Volcanoes National Park in April 2005, ever increasing the size of the island|alt=Photo showing clouds of steam surrounding lava that is partly black and partly glowing orange The Great Crack is an , and fissure in the island, in the district of
Kaū. According to the United States Geological Survey (USGS), the Great Crack is the result of crustal dilation from
magmatic intrusions into the southwest rift zone of
Kīlauea. While neither the
earthquake of 1868 nor that of 1975 caused a measurable change in the Great Crack, lava welled out of its lower in 1823.
Hilina Slump , one of the most famous
black sanded beaches|alt=Photo of coastline with 10 people standing or walking on the beach and palm trees in background , also known as "Magic Sands", located in
Kailua-Kona The
Hilina Slump is a section of the south slope of Kīlauea that is moving away from the island. Between 1990 and 1993,
Global Positioning System (GPS) measurements showed a southward displacement of about per year. Undersea measurements show a "bench" that has formed a buttress and that this buttress may tend to reduce the likelihood of catastrophic detachment.
Earthquakes and tsunamis On 2 April 1868,
an earthquake with a magnitude estimated between 7.25 and 7.9 rocked the southeast coast of Hawaii. This was the most destructive earthquake in the Hawaii's recorded history. It triggered a
landslide on
Mauna Loa, north of
Pāhala, killing 31 people. A
tsunami claimed 46 more lives. The villages of
Punaluu,
Nīnole, Kāwāa,
Honuapo, and
Keauhou were severely damaged. The tsunami reportedly rolled over the tops of the coconut trees up to high, and it reached inland a distance of a quarter of a mile (400 meters) in some places. On 29 November 1975, a section of the Hilina Slump dropped and slid toward the ocean. This movement caused a 7.2 magnitude earthquake and a tsunami. Oceanfront property was washed off its foundations in Punaluu. Two deaths were reported at Halape, and 19 other people were injured. The island suffered damage from a tsunami caused by earthquakes in
Alaska on 1 April 1946, and in
Chile on 23 May 1960. Downtown
Hilo was damaged by both tsunamis, with many lives lost. Just north of Hilo,
Laupāhoehoe lost 16 schoolchildren and five teachers in the tsunami of 1946. In March 2011, a
9.0 magnitude earthquake off the east coast of Japan again created a tsunami that caused minor damage in Hawaii. The estimated damage to public buildings was about US$3 million. In the
Kona area this tsunami washed a house into
Kealakekua Bay, destroyed a yacht club and tour boat offices in
Keauhou Bay, caused extensive damage in
Kailua-Kona, flooded the ground floor of the King Kamehameha Hotel, and temporarily closed the Kona Village Resort. In early May 2018,
hundreds of small earthquakes were detected on Kīlauea's East
Rift Zone, leading officials to issue evacuation warnings. On 3 May 2018, the volcano erupted in Puna after a 5.0 earthquake earlier in the day, causing evacuations of
Leilani Estates and Lanipuna Gardens subdivisions. A seemingly related 5.3 magnitude quake and a subsequent
6.9 magnitude earthquake occurred on 4 May.
Volcanic fog ) measuring station in Hawaii
Vog (volcanic fog) can envelop the island of Hawaii when Kīlauea is active. Since the termination of volcanic activity in September 2018, vog has largely disappeared on the west side of the island. The gas plumes created a blanket of vog that the
trade winds mostly deflect toward the Kona coast. Vog can damage the health of plants, humans, and other animals. Most of the
aerosols are acidic and of a size where they can remain in the lungs to damage them. Flu-like symptoms and general lethargy are reported, and are especially pronounced in people with respiratory conditions.
National protected areas blossoms, HawaiiThe island hosts many specialized ecosystems/microclimates, including many protected by federal designation: •
Ala Kahakai National Historic Trail •
Hakalau Forest National Wildlife Refuge •
Hawaii Volcanoes National Park •
Kaloko-Honokōhau National Historical Park •
Kohala Historical Sites State Monument (
Mookini Heiau) •
Kona Forest National Wildlife Refuge •
Puuhonua o Hōnaunau National Historical Park •
Puukoholā Heiau National Historic Site File:Downtown Kona, Hawaii.jpg|Downtown
Kailua-Kona File:Downtown Hilo, Hawaii.jpg|Downtown
Hilo == Economy ==