Every fact in the three volcano lessons is listed here with where it comes from. The numbers in [brackets] on the lesson pages link to this list.
How we rate sources
High: space agencies (NASA), peer-reviewed open textbooks (OpenStax, Rice University) and professional scientific societies (American Physical Society).
Medium-high: reputable science news reporting directly on a primary document.
Medium: single-author essays and popular history sites. We only use these for history details, and never on their own: each one is paired with a second source.
Wikipedia was not used as a source. Numbers are rounded (for example 9.8 m/sΒ² for Earth's gravity). The text was drafted with help from AI (Claude) and then checked against these sources. Corrections: hello@echoesof.science.
Where the lessons simplify: counts of volcanoes depend on the definition: the USGS gives about 1,350 potentially active volcanoes worldwide, while the British Geological Survey says more than 1,500 active volcanoes; the lessons give both and say why they differ. The fizzy volcano for ages 6β7 is only a model: the bubbles come from a reaction between baking soda and vinegar, not from melted rock, and the lesson says so. The 'lava race' for ages 10β11 and the bubble test for ages 15β16 use kitchen liquids to model how thick or runny magma is; real magma is far hotter and its stickiness also depends on temperature and crystals, which the lessons leave out. The sorting games put each volcano type in one group; real volcanoes can change their style of eruption.
All sources
[1] How do volcanoes erupt?
US Geological Survey (USGS) Β· Reliability: High
Type: Government science agency FAQ
Rock deep underground can melt into magma; because it is lighter than the solid rock around it, magma rises and collects in magma chambers; some of it pushes through vents and fissures; magma that has erupted is called lava; if magma is thin and runny, gases escape easily and it flows out of the volcano (example: Hawaii's volcanoes); if magma is thick and sticky, gases cannot escape easily, pressure builds until the gases escape violently and explode (example: Mount St. Helens); ash erupted into the sky falls back to Earth like powdery snow; when hot volcanic materials mix with water from streams or melted snow and ice, mudflows form.
Volcanoes are openings, or vents, where lava, tephra (small rocks) and steam erupt onto the Earth's surface; magma is molten rock below the surface with crystals and dissolved gas, and is called lava once erupted; cinder cones are the simplest type, small and built from pieces of lava; composite volcanoes (stratovolcanoes) are tall and steep, made of repeating layers of lava flows, ash, cinders, blocks and bombs; shield volcanoes are built almost entirely of fluid lava flows and form broad, gently sloping domes; lava domes are lava too thick to flow away from the vent and can collapse, sending hot rock and gas down the slope; the finest ash can be carried by winds for many miles.
There are about 1,350 potentially active volcanoes worldwide; about 500 of them have erupted in historical time; most earthquakes and volcanic eruptions do not strike randomly but occur in specific areas.
Volcanic arcs and oceanic trenches partly encircling the Pacific Basin form the so-called Ring of Fire, a zone of frequent earthquakes and volcanic eruptions; volcanic island arcs lie parallel to and landward of the trenches.
[5] This Dynamic Earth: Understanding plate motions
US Geological Survey (USGS) Β· Reliability: High
Type: Government science agency booklet
At divergent boundaries plates move apart and new crust is created by magma pushing up from the mantle; at convergent boundaries plates move toward each other and sometimes one sinks (is subducted) under another; the Mid-Atlantic Ridge spreads on average about 2.5 cm per year; oceanic-continental convergence sustains many of the Earth's active volcanoes, such as the Andes and the Cascade Range.
Hotspots are relatively small, long-lasting, exceptionally hot regions in the mantle that supply heat for volcanoes far from plate boundaries; the Hawaiian chain formed as the Pacific Plate moved over a deep, stationary hotspot; plate movement carries each island beyond the hotspot, cutting it off from its magma, and a new volcano forms over the hotspot; rocks on Kauai are about 5.5 million years old, while the oldest exposed rocks on the Island of Hawaii are less than 0.7 million years old; some hotspots lie near the mid-ocean ridge, such as beneath Iceland.
The eruption temperature of KΔ«lauea lava is about 1,170 Β°C; lava in tubes is about 1,250 Β°C; yellow glowing lava is about 1,000β1,200 Β°C, orange about 800β1,000 Β°C and red about 600β800 Β°C.
British Geological Survey (BGS) Β· Reliability: High
Type: National geological survey education page
There are more than 1,500 active volcanoes on Earth, and volcanoes erupt roughly 50 to 70 times a year; some, such as Etna and Stromboli, erupt almost continuously, while others stay quiet for centuries or longer; eruptions can be explosive, sending ash, gas and magma high into the atmosphere, or effusive, producing lava flows and domes; different types of volcano form according to the properties of the magma; most volcanoes on Earth are not well monitored or not monitored at all.
[9] Magma Composition and Eruption Style (Physical Geology, section 4.2)
Physical Geology, open university textbook (eCampusOntario Pressbooks) Β· Reliability: Medium-high
Type: Open university textbook
Felsic magmas are more viscous because they have more silica; felsic magmas have 4% to 7% volatiles, intermediate 3% to 4% and mafic magmas typically 1% to 3%; the most abundant volatile is water, followed by carbon dioxide and then sulphur dioxide; in viscous magma gas cannot escape easily, pressure builds and leads to an explosive eruption; mantle plume and spreading-ridge magmas tend to be mafic, so effusive eruptions are the norm.
Physical Geology, open university textbook (BCcampus OpenText) Β· Reliability: Medium-high
Type: Open university textbook
Most volcanoes are associated with convergent plate boundaries (subduction zones); there is much volcanic activity at divergent boundaries and areas of continental rifting; composite volcanoes are normally associated with subduction; most shield volcanoes are associated with mantle plumes and erupt mafic lava flows; pyroclastic density currents can move at hundreds of km/h; lahars (volcanic mudflows) can destroy entire towns; lava flows move slowly enough for people to escape; prediction methods include monitoring earthquakes in volcanic regions, detecting volcanic gases and measuring deformation of a volcano's flanks.