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The Hawaiian Islands are home to some of the most iconic and active composite volcanoes in the world. If you’re wondering how these massive volcanoes formed and what makes them so unique, you’ve come to the right place.

Composite volcanoes, also known as stratovolcanoes, are some of the most explosive and dangerous in the world due to their steep slopes and tendency to erupt explosively and release ash, lava, and volcanic gases. The Hawaiian Islands were formed by hotspots in the mantle plume that continue to erupt effusively, forming gently sloping shield volcanoes followed by steeper composite volcanic cones.

In this nearly 3000 word article, we will cover the key features of Hawaiian composite volcanoes, how they form, the major hazards they pose, and take an in-depth look at the most famous composite volcanoes in Hawaii like Mauna Loa, Mauna Kea, and Haleakala.

What Are Composite Volcanoes?

Composite volcanoes, also known as stratovolcanoes, are a type of volcano characterized by their tall and steep cone-shaped structure. They are formed through explosive eruptions that eject a combination of lava flows, ash, and other volcanic materials. Unlike shield volcanoes, which have broad and gently sloping sides, composite volcanoes have a more symmetrical shape with steep sides.

Definition and Key Characteristics

Composite volcanoes are composed of alternating layers of lava flows and pyroclastic materials such as ash, pumice, and volcanic bombs. These layers are formed as a result of the alternating eruptions of both viscous and explosive magma. The lava flows from composite volcanoes are usually more viscous and cooler than those from shield volcanoes, which causes them to be less fluid and form steeper slopes.

One of the key characteristics of composite volcanoes is their tendency to produce explosive eruptions. The buildup of pressure within the volcano’s magma chamber can result in violent eruptions that send ash clouds, pyroclastic flows, and volcanic bombs high into the air. These eruptions can be highly hazardous to nearby communities and can cause significant damage to the surrounding environment.

Differences from Shield Volcanoes

While shield volcanoes and composite volcanoes are both types of volcanoes, they have distinct differences in terms of their shape, eruption style, and composition. Shield volcanoes, such as those found in Hawaii, are characterized by their broad, gently sloping sides and are formed through the eruption of fluid lava that flows easily over long distances.

On the other hand, composite volcanoes have a more conical shape and are built up by alternating eruptions of viscous lava and explosive pyroclastic materials. The lava from composite volcanoes is thicker and less fluid, resulting in steeper slopes. These volcanoes also tend to have more explosive eruptions, which can be attributed to the higher silica content in their magma.

How Do Composite Volcanoes in Hawaii Form?

Composite volcanoes, also known as stratovolcanoes, are formed through a complex process involving multiple phases of growth and the unique geology of the Hawaiian Islands. Let’s take a closer look at how these magnificent volcanic structures come into existence.

Origins in the Hawaiian hotspot

The Hawaiian Islands owe their existence to a hot spot in the Earth’s mantle, where molten rock, or magma, rises to the surface. This hot spot remains stationary while the Pacific tectonic plate slowly moves over it, creating a chain of volcanic islands. As the plate moves, new volcanoes form over the hot spot, while older ones become dormant and eventually erode away.

The magma that feeds these volcanoes is rich in silica, making it highly viscous and prone to explosive eruptions. This high viscosity is due to the presence of gases, such as water vapor and carbon dioxide, which get trapped in the magma as it rises to the surface.

Phases of growth

Composite volcanoes go through several phases of growth, each contributing to their distinctive shape and structure. Initially, eruptions are characterized by explosive activity, with ash, rocks, and lava fragments being ejected into the air. These eruptions build up layers of volcanic materials, including ash, pumice, and volcanic bombs, creating a steep and conical shape.

Over time, as the volcano continues to erupt, lava flows begin to dominate the eruptions. These lava flows are typically thick and slow-moving, with the ability to travel long distances. As they cool and solidify, they add additional layers to the volcano’s structure, gradually increasing its size and height.

Magma composition

The composition of the magma that forms composite volcanoes in Hawaii is primarily basaltic, which means it is rich in iron and magnesium. This type of magma is relatively low in silica content, resulting in less viscous eruptions. As a result, eruptions tend to be more effusive, with the lava flowing more freely and covering larger areas.

It is worth noting that the composition of the magma can vary from one volcano to another, leading to differences in eruption styles and volcanic behavior. For example, some composite volcanoes in Hawaii have experienced more explosive eruptions due to the presence of more silica-rich magma.

To learn more about composite volcanoes in Hawaii and their fascinating formation process, you can visit the National Park Service’s official website for Hawaii Volcanoes National Park. Here, you can explore detailed information about the volcanoes, their history, and ongoing research efforts.

Hazards of Hawaiian Composite Volcanoes

Hawaiian composite volcanoes are not only breathtaking natural wonders, but they also pose various hazards to the surrounding areas. These hazards include pyroclastic flows and surges, lava flows, landslides and sector collapse, and lahars and flooding.

Pyroclastic flows and surges

One of the most dangerous hazards associated with composite volcanoes in Hawaii is the occurrence of pyroclastic flows and surges. These are fast-moving currents of hot gas, ash, and volcanic material that can travel down the slopes of the volcano at incredible speeds, reaching temperatures of up to 1,000 degrees Celsius. Pyroclastic flows and surges can cause extensive damage to infrastructure and pose a significant risk to human life. It is crucial for residents and tourists to be aware of evacuation routes and follow the guidance of local authorities in case of an eruption.

Lava flows

Lava flows are another prominent hazard associated with Hawaiian composite volcanoes. These molten streams of lava can move slowly or rapidly, depending on the viscosity of the lava. While slow-moving lava flows may give people time to evacuate, fast-moving flows can be unpredictable and pose a significant threat to nearby communities. In the past, lava flows have destroyed homes, roads, and other infrastructure. It is essential to stay informed about the current lava flow activity and adhere to evacuation orders to ensure personal safety.

Landslides and sector collapse

Landslides and sector collapse are hazards that can occur during volcanic eruptions, especially on Hawaiian composite volcanoes. The accumulation of loose volcanic material on the steep slopes of the volcano can make it prone to landslides and collapses. These events can trigger destructive avalanches, causing widespread damage and posing risks to those in the vicinity. Monitoring and early warning systems are vital in identifying potential landslides and sector collapses, allowing for timely evacuation and mitigation efforts.

Lahars and flooding

Lahars and flooding are hazards that can arise from volcanic eruptions on Hawaiian composite volcanoes. Lahars are fast-moving mudflows that can occur when volcanic material mixes with water, usually from heavy rainfall or melting ice and snow. These lahars can travel down valleys and river channels, posing a significant threat to communities downstream. Additionally, volcanic eruptions can cause flooding due to the melting of glaciers and ice caps. It is crucial for residents in vulnerable areas to be aware of the potential for lahars and flooding and take necessary precautions to ensure their safety.

Case Studies of Famous Hawaiian Composite Volcanoes

Mauna Loa

Mauna Loa is one of the most renowned composite volcanoes in the world, located on the Big Island of Hawaii. It is the largest volcano on Earth, with an estimated volume of over 18,000 cubic miles. Mauna Loa is known for its frequent eruptions and lava flows that have shaped the island’s landscape over thousands of years. The volcano’s gentle slopes and shield-like form make it a prime example of a composite volcano. It has erupted 33 times since its first well-documented eruption in 1843, with the most recent eruption occurring in 1984. The Mauna Loa Observatory, situated on the volcano, collects valuable data on atmospheric conditions and serves as an important research center for climate studies.

Mauna Kea

Mauna Kea is another iconic composite volcano in Hawaii, located on the same Big Island as Mauna Loa. Though it is slightly shorter than Mauna Loa, Mauna Kea is recognized for its exceptional height, towering above the surrounding landscape at 13,796 feet. While it may seem surprising, Mauna Kea is considered the world’s tallest mountain when measured from its base on the ocean floor. This dormant volcano has not erupted for thousands of years, but its summit is home to numerous astronomical observatories due to its clear skies and minimal light pollution. These observatories contribute to significant scientific discoveries and are crucial for our understanding of the universe.


Located on the island of Maui, Haleakalā is a composite volcano that attracts visitors from all over the world. Its name translates to “House of the Sun” in Hawaiian, and it is renowned for its breathtaking sunrises and panoramic views. Haleakalā last erupted in the late 17th century, making it currently dormant. The volcano’s summit area is a national park and offers a unique environment with diverse flora and fauna. Hiking trails allow visitors to explore the volcanic landscape and witness the striking colors of the cinder cones and lava fields. The Haleakalā Observatory, situated near the summit, provides valuable astronomical research and observation opportunities.


The composite volcanoes of Hawaii are iconic landmarks that have built up the Hawaiian Islands over hundreds of thousands of years through repeated eruptive stages. Their explosive nature and steep slopes make them hazardous, but also create breathtaking landscapes.

Understanding how these volcanoes form through the Hawaiian hotspot and their key volcanic hazards helps us appreciate the natural forces that built Hawaii and remain active to this day.

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