Shield volcanoes are some of the largest volcanoes on Earth, known for their enormous size and relatively gentle slope. The Hawaiian Islands were formed by a chain of shield volcanoes that erupted from a hot spot deep beneath the Pacific Ocean floor. If you’re short on time, here’s a quick answer to your question: Shield volcanoes in Hawaii are characterized by their enormous size, low slope, steady lava flow, and caldera at the summit that forms when the top collapses.
In this approximately 3000 word article, we will explore what makes Hawaiian shield volcanoes unique, how they erupt and build the islands over time, and examine the most famous and active shield volcanoes in Hawaii like Mauna Loa and Kilauea.
What Are Shield Volcanoes?
If you’ve ever seen a picture of the Hawaiian Islands, you’ve likely marveled at the majestic, gently sloping mountains that seem to rise out of the ocean. These iconic landforms are known as shield volcanoes, named for their resemblance to a warrior’s shield lying on the ground. Shield volcanoes are a unique type of volcano characterized by their shape, eruption style, and composition.
Gentle slope and large size
One of the defining features of shield volcanoes is their gentle slope. Unlike other types of volcanoes, such as stratovolcanoes with steep sides, shield volcanoes have a broad, low-angle profile. This shape is a result of the lava flows that are emitted during their eruptions. The lava, which is typically low in viscosity and high in temperature, spreads out evenly over the surrounding landscape, creating a wide, shallow cone.
Shield volcanoes are also known for their impressive size. In fact, they are some of the largest volcanoes on Earth. Mauna Loa, located in Hawaii, is the largest shield volcano in the world, with a volume of approximately 18,000 cubic kilometers. To put that into perspective, Mauna Loa is taller than Mount Everest when measured from its base on the ocean floor to its summit above sea level. Its massive size is a testament to the long periods of volcanic activity that have built up the volcano over thousands of years.
Steady, non-explosive eruptions
Unlike some other types of volcanoes that have explosive eruptions, shield volcanoes are known for their relatively calm and non-explosive activity. This is because the lava that erupts from shield volcanoes is typically low in silica content, which results in low viscosity. The low viscosity allows the lava to flow easily and smoothly, rather than building up pressure and causing explosive eruptions.
Instead of explosive eruptions, shield volcanoes often have what is known as effusive eruptions. During these eruptions, the lava flows steadily from the volcanic vent, slowly building up the shield-shaped cone over time. This continuous, non-explosive activity is one of the reasons why shield volcanoes can grow to such large sizes.
Layered lava flows
Another characteristic feature of shield volcanoes is their layered lava flows. As the lava spreads out over the landscape, it cools and solidifies, forming layers of solidified rock. These layers can be seen in the exposed sides of the volcano, revealing the history of past eruptions.
Each layer represents a different period of volcanic activity, with older layers at the bottom and younger layers towards the top. By studying these layers, scientists can gain valuable insights into the volcano’s eruption history and the processes that have shaped the landscape over time.
For more information about shield volcanoes, you can visit the United States Geological Survey (USGS) website. It provides detailed information about shield volcanoes and their unique characteristics.
Hawaiian Hot Spot and Chain of Islands
The Hawaiian Islands are a remarkable result of volcanic activity that has been ongoing for millions of years. This volcanic activity is attributed to a deep mantle plume, or a column of hot, buoyant material rising from deep within the Earth. The Hawaiian hot spot is located in the central Pacific Ocean, and it is responsible for the creation of the chain of islands that make up the Hawaiian archipelago.
Deep mantle plume
The deep mantle plume beneath Hawaii is a fascinating geological phenomenon. It is believed to be a result of a particularly hot and active region in the Earth’s mantle, which lies beneath the Pacific tectonic plate. As the Pacific plate moves slowly over the hot spot, magma rises to the surface, creating volcanic activity. This process has been ongoing for millions of years, leading to the formation of the Hawaiian Islands.
Islands formed in sequence
The formation of the Hawaiian Islands is not random but rather follows a distinct pattern. Each island in the chain is formed as the Pacific plate moves gradually over the hot spot. The oldest island, Kauai, is located at the northwest end of the chain, while the youngest island, Hawaii (also known as the Big Island), is situated at the southeast end. This sequence of islands provides valuable evidence of the progression of volcanic activity over time.
Evidence of evolution
The Hawaiian Islands also offer a unique opportunity to study the evolution of shield volcanoes. Shield volcanoes are characterized by their broad, gently sloping shape and are formed by the accumulation of multiple layers of lava flows. The islands in the Hawaiian chain exhibit different stages of volcanic activity, with older islands showing eroded volcanic peaks and younger islands displaying active volcanic activity.
Scientists have conducted extensive research on the Hawaiian Islands to understand the processes involved in shield volcano formation and evolution. These studies have provided valuable insights into the behavior of magma, the movement of tectonic plates, and the long-term geological processes that shape our planet.
If you’re interested in learning more about shield volcanoes and the Hawaiian Islands, you can visit the National Park Service website, which offers detailed information and resources on this topic.
Eruptive Activity of Shield Volcanoes
Shield volcanoes, such as those found in Hawaii, are known for their relatively gentle eruptions compared to other types of volcanoes. This is due to the type of lava they produce and the way it flows.
Fluid, basaltic lava
Shield volcanoes are characterized by the eruption of fluid, basaltic lava. This type of lava has a low viscosity, meaning it flows easily and spreads out over large distances. As a result, eruptions from shield volcanoes tend to be less explosive and more effusive.
The basaltic lava that erupts from shield volcanoes is rich in iron and magnesium. It has a relatively low silica content, which contributes to its fluidity. This lava is also hot, reaching temperatures of around 1,200 to 1,400 degrees Celsius (2,200 to 2,600 degrees Fahrenheit).
Fire fountains and lava lakes
During eruptions, shield volcanoes can produce spectacular fire fountains and lava lakes. These phenomena occur when the pressure of the magma beneath the volcano forces it to erupt through a vent or fissure in the Earth’s surface.
Fire fountains are vertical jets of lava that shoot up into the air. They can reach heights of several hundred meters (over a thousand feet). Lava lakes, on the other hand, form when a crater or vent fills with lava and creates a pool-like feature on the volcano’s surface.
These fire fountains and lava lakes are a result of the high gas content in the basaltic lava. As the magma rises to the surface, the decrease in pressure allows the dissolved gases, such as water vapor and carbon dioxide, to expand and escape, propelling the lava into the air.
Another characteristic of shield volcanoes is the potential for caldera collapse. As the volcano erupts and the magma chamber empties, the weight of the volcano can cause the summit to collapse inward, creating a large, circular depression known as a caldera.
The collapse of the caldera can be triggered by the withdrawal of magma during an eruption or by the intrusion of magma into the subsurface, causing the overlying rock to become unstable. The collapse can occur gradually over time or can happen suddenly, resulting in a catastrophic event.
An example of a shield volcano with a collapsed caldera is Mauna Loa in Hawaii. Its summit caldera, known as Mokuʻāweoweo, is approximately 12 kilometers (7.5 miles) wide and 400 meters (1,300 feet) deep.
Understanding the eruptive activity of shield volcanoes is crucial for scientists and local communities in volcanic areas. By studying these volcanoes and their eruptions, researchers can gain valuable insights into volcanic behavior and improve their ability to forecast and mitigate volcanic hazards.
Famous Hawaiian Shield Volcanoes
Mauna Loa is one of the most iconic shield volcanoes in Hawaii. It is the largest volcano on Earth by volume and stands at an impressive 13,678 feet above sea level. With its gently sloping sides and broad summit, Mauna Loa is a classic example of a shield volcano. It has erupted 33 times since its first well-documented eruption in 1843, making it one of the most active volcanoes in the world. The eruptions of Mauna Loa have produced extensive lava flows that have reached the ocean, creating new land and expanding the size of the Big Island of Hawaii. If you’re lucky, you may even witness one of Mauna Loa’s awe-inspiring eruptions!
Kilauea, located on the southeastern side of the Big Island of Hawaii, is one of the most active volcanoes in the world. It has been erupting continuously since 1983, making it the longest-lasting eruption in recorded history. Kilauea is known for its dramatic lava flows, which have destroyed homes, roads, and even entire communities. Despite its destructive power, Kilauea also offers a unique opportunity to witness the creation of new land. Visitors can hike to the edge of the lava flows and watch as molten rock spills into the ocean, creating steam and explosions. It’s a sight that will leave you in awe of nature’s raw power.
Rising 10,023 feet above sea level, Haleakala is a majestic shield volcano located on the island of Maui. Its name means “house of the sun” in Hawaiian, and it is a popular destination for tourists and locals alike. Haleakala is best known for its stunning sunrise and sunset views. From the summit, you can witness the sun breaking through the clouds, casting a golden glow over the volcanic landscape. It’s a sight that will take your breath away and leave you feeling connected to the natural beauty of Hawaii.
Mauna Kea, which means “white mountain” in Hawaiian, is a dormant shield volcano that reaches a height of 13,796 feet, making it the tallest mountain in Hawaii. It is renowned for its world-class observatories, which take advantage of the mountain’s high elevation and clear skies to study the stars and galaxies. Mauna Kea is considered one of the best places in the world for astronomical research, and its summit provides a unique opportunity for stargazing. If you visit Mauna Kea, make sure to dress warmly, as temperatures can drop below freezing at night!
Kohala is the oldest of the five shield volcanoes that make up the Big Island of Hawaii. It is estimated to be around one million years old and has been dormant for over 60,000 years. Kohala’s gentle slopes and lush vegetation make it a popular destination for hiking and exploring. The volcano is home to beautiful valleys, waterfalls, and stunning views of the surrounding landscape. It’s a tranquil and peaceful place that offers a glimpse into the geological history of Hawaii.
Hazards and Monitoring
Shield volcanoes in Hawaii can be both fascinating and dangerous. While their gently sloping sides and relatively calm eruptions make them less explosive than other types of volcanoes, there are still hazards associated with their activity. It is important to understand these hazards and have effective monitoring systems in place to protect the communities living near these volcanoes.
One of the primary hazards associated with shield volcanoes is the potential for lava flows. As these volcanoes erupt, molten lava can flow downhill, covering vast areas of land. While lava flows tend to move relatively slowly, they can still pose a threat to nearby communities, infrastructure, and natural resources.
Efforts are made to monitor the movement and direction of lava flows to provide early warnings to residents. The Hawaiian Volcano Observatory, operated by the United States Geological Survey (USGS), closely monitors the activity of shield volcanoes in Hawaii. Through a network of sensors and observatories, they track the movement of lava and provide real-time updates to local authorities and the public.
Volcanic smog (vog)
Another hazard associated with shield volcanoes in Hawaii is volcanic smog, also known as vog. Vog is formed when volcanic gases, such as sulfur dioxide, react with oxygen and other atmospheric components. This can lead to the formation of sulfuric acid particles, which can irritate the respiratory system and cause health issues, particularly for individuals with pre-existing respiratory conditions.
Monitoring vog levels is crucial to ensure the well-being of the communities living near shield volcanoes. The USGS and the Hawaii Department of Health regularly monitor the air quality and provide updates on vog levels. They also advise residents on how to protect themselves, such as staying indoors when vog levels are high and using air purifiers.
Continuous monitoring of shield volcanoes is essential for understanding their behavior and predicting eruptions. The Hawaiian Volcano Observatory utilizes a range of techniques to monitor the activity of these volcanoes, including seismic monitoring, gas measurements, and thermal imaging.
Seismic monitoring involves the use of sensitive instruments to detect and analyze ground vibrations caused by volcanic activity. Gas measurements help scientists understand the composition and quantity of gases being released by the volcano, which can provide important clues about its activity. Thermal imaging allows scientists to detect changes in temperature, which can indicate the movement of magma beneath the volcano’s surface.
By combining these monitoring methods, scientists can gain a better understanding of the behavior of shield volcanoes and provide valuable information to help authorities make informed decisions about the safety of nearby communities.
Hawaii’s iconic shield volcanoes have built the Hawaiian Islands over millions of years through their steady, non-explosive eruptions of fluid lava. These gentle giants allow unique insights into the deep hot spot driving volcanism on Hawaii. Though normally not explosive, Hawaiian volcanoes still pose hazards from lava flows, volcanic smog, and collapse events. Continued monitoring and research helps keep people safe and learns more about these volcanic wonders.
Through this deep dive into shield volcanoes in Hawaii, we explored how they form, erupt over time, the specific volcanoes that built each island, and the potential risks these volcanoes can pose. Hawaii’s volcanoes showcase these volcanic mountains in their classic shield shape and behavior, helping understand volcanism around the world.