Mauna Ulu: Birth of a Growing Mountain in Hawaiʻi Volcanoes National Park
Discover the epic story of Mauna Ulu, the 'growing mountain,' formed through years of explosive volcanic activity in Hawaiʻi Volcanoes National Park.
Mauna Ulu: The “Growing Mountain” of Kīlauea
Mauna Ulu stands as one of the most remarkable volcanic formations within Hawaiʻi Volcanoes National Park. Its Hawaiian name, meaning “the growing mountain,” perfectly encapsulates its dramatic rise from Kīlauea’s lava fields between 1969 and 1974. Today, Mauna Ulu offers both scientists and visitors a vivid glimpse into the power and beauty of volcanic activity on the Big Island of Hawaiʻi.
In This Article
- Eruption History and Formation
- Stages and Impact of the Mauna Ulu Eruption
- Physical Features & Landscape
- Scientific Significance
- Visiting Mauna Ulu: Trails & Tips
- Frequently Asked Questions
Eruption History and Formation
The creation of Mauna Ulu began on May 24, 1969, when fissures erupted along the East Rift Zone of Kīlauea volcano. Over 1,774 days—until July 22, 1974—it became the longest-lasting and most voluminous flank eruption recorded at Kīlauea in over 2,200 years.
- Duration: May 24, 1969 – July 22, 1974
- Total Lava Output: Approx. 350 million m³
- Area Covered: About 44 km² of new lava field
- Lava Depth in Places: Up to 7.6 meters
- Destruction: Parts of Chain of Craters Road buried by lava flows
- Height of Lava Fountains: Notably, one fountain reached 539.5 meters
Stages and Impact of the Mauna Ulu Eruption
Mauna Ulu’s development is a story of multiple eruptive phases, each contributing to the landscape and scientific knowledge.
Initial Outbreak and Lava Fountains (1969)
- First Day: Two main fountaining zones erupted for periods of 18 and 36 hours. The western fountains cut the Chain of Craters Road, limiting direct observation.
- High lava fountains, up to several hundred meters, sent rivers of molten lava downslope, filling ‘Ālo‘i and Ala‘e pit craters, some of which filled with over 25 meters of lava before draining back into fissures.
- Lava fountains built a tephra cone of 50 m (covered later by lava up to 70 m), which would be later called Mauna Ulu.
Formation of the Shield and Prolonged Activity (1970-1971)
- Lava flows became more steady and effusive, contributing to the rapid buildup of the Mauna Ulu shield—eventually 80 meters high.
- Lava flows spread both overland and via tubes all the way to the Pacific Ocean, creating dramatic coastal entries and expanding the volcano’s land mass.
- Lava periodically surged into pit craters, creating transient lava lakes and allowing scientists to observe rare volcanic phenomena.
Later Stages & Cessation (1972-1974)
- After a short pause from October 1971 to February 1972, the eruption resumed with new vents opening along the east flank of the growing shield.
- Lava tube networks developed, feeding both surface and subsurface flows toward the sea and further enhancing the landscape’s complexity.
- The eruption concluded in July 1974, leaving a legacy as one of the 20th century’s most intensively studied volcanic episodes at Kīlauea.
Physical Features & Landscape
The Mauna Ulu area is a dynamic volcanic field of black lava flows, cinder, and shattered native forest. The landforms here were shaped by explosive fountains, shifting tube systems, and the relentless encroachment of lava on the landscape.
Key Geologic Features
- Mauna Ulu Cone: A 70+ meter high feature made of overlapping flows and thick layers of welded tephra, pumice, and reticulite. Its summit crater reflects the consequences of explosive fountaining and subsequent collapse.
- Lava Tubes: Subterranean passages, once filled with flowing lava, now serve as conduits for cooled rock and are occasionally visible where roofs have collapsed.
- Tree Molds: Vertical casts left by trees engulfed in lava—a striking testament to the interaction between volcanic force and existing ecosystem.
- Surface Features: Vast, billowy pāhoehoe and jagged ‘a‘ā textures: these different types of flows offer an open-air geologic textbook for visitors and researchers alike.
| Attribute | Detail |
|---|---|
| Duration | 5 years (1969-1974) |
| Lava Volume | ~350 million m³ |
| Area Covered | 44 km² |
| Highest Fountain | 539.5 meters |
| Shield Height | ~80 meters |
Scientific Significance
The Mauna Ulu eruption became a pivotal event for modern volcanology and geoscience. It prompted breakthrough studies and observations that have shaped our current understanding of dynamic volcanic processes.
- Pāhoehoe vs. ‘A‘ā Formation: Long-term close-up observation led to clearer understanding of the conditions that produce pāhoehoe (smooth, ropy lava) versus ‘a‘ā (rough, clinkery lava).
- Pillow Lava Research: For the first time, pillow lava forming underwater was filmed and documented by divers, revealing crucial insights into how submarine flows contribute to oceanic landform expansion.
- Lava Lake & Gas Pistoning: Mauna Ulu hosted persistent lava lakes, offering valuable data on gas-driven pistoning events—periodic degassing and surging of lava.
- Lava Tube Networks: Systematic mapping and observation improved scientists’ ability to model how lava tubes distribute flow over great distances while protecting molten rock from cooling before reaching the ocean.
- Tree Molds & Ecological Impact: The eruption’s interaction with native Hawaiian rainforest produced dramatic tree molds—vertical lava casts formed when lava engulfed trees, preserving their shape in stone.
Visiting Mauna Ulu: Trails & Tips
Today, Mauna Ulu is one of the most accessible and geologically instructive volcanoes in the world, located near the Chain of Craters Road in Hawaiʻi Volcanoes National Park.
Highlights of the Mauna Ulu Hike
- Mauna Ulu Trail: A moderately strenuous hike leads visitors across surreal lava fields, past pit craters, and up to panoramic views from the cone itself.
- Unique sights include still-smoking cracks, cooled lava rivers, and spectacular rainforest regrowth on sections undisturbed by recent flows.
- Key stops include ‘Ālo‘i and Ala‘e pit craters—now dramatically altered from their original forms.
Essential Advice for Visitors
- Gear: Wear sturdy closed-toe shoes (lava is abrasive), a hat, and sun protection.
- Water: Bring more than you think you’ll need; the landscape is exposed and hot.
- Navigation: Trails are marked by rock cairns, but can be easy to lose among undulating lava. Bring a map or GPS.
- Safety: Do not approach vents or recent lava flows. The terrain can shift, and hazardous volcanic gases may be present.
- Respect: This is an area of cultural significance and ongoing natural change—leave only footprints and take only photographs.
Frequently Asked Questions (FAQs)
Q: What does “Mauna Ulu” mean?
A: In Hawaiian, Mauna Ulu translates as “the growing mountain,” reflecting its rapid buildup during the five-year eruption period.
Q: Is it possible to hike to Mauna Ulu’s summit?
A: Yes, a marked trail leads to the summit, offering breathtaking views of the cone, surrounding flows, and pit craters. Hikers should be prepared for challenging terrain and changing weather conditions.
Q: How did the Mauna Ulu eruption change scientific understanding?
A: The eruption was a landmark event in volcanology, allowing scientists to document the evolution of shield volcanoes, lava tubes, and underwater pillow lava in great detail for the first time.
Q: What wildlife or plants can be found near Mauna Ulu?
A: Between flows, you may spot resurgent native forest, pioneering ferns, and birds such as the yellow ‘amakihi and the Hawaiian hawk (‘io) in untouched kipuka (islands of forest).
Q: Can lava still be seen at Mauna Ulu?
A: While Mauna Ulu itself is dormant, eruptions elsewhere on Kīlauea occasionally reach the area. Always check with park authorities for current volcanic activity before your visit.
Tips for Making the Most of Your Visit
- Start Early: The area is exposed and hot later in the day.
- Stay on Trails: Protect delicate lava surfaces and native plants regenerating on the margins.
- Photography: Sunrise and sunset produce enchanting colors on the cinder fields.
- Learn Local Legends: Mauna Ulu and surrounding craters are tied to many stories within Hawaiian culture; ranger-led hikes can provide fascinating context.
- Plan Ahead: Weather can be unpredictable, and parts of the park may close due to hazards—check conditions before departing.
The Enduring Essence of Mauna Ulu
Mauna Ulu, forged by nearly five years of continuous volcanic activity, stands as a defining feature of Hawaiʻi Volcanoes National Park—a living classroom for earth science, a testament to nature’s power, and an awe-inspiring destination for any visitor with a sense of wonder.
