A Giant Baumkuchen Carved in Stone! 18,000 Years Etched into Izu Oshima’s Cliffside Strata
I’m Ken Kuwako, the Science Trainer. Every day is an experiment.
Imagine standing in front of a towering cliff, tens of meters high, covered with perfectly layered brown stripes that look as though they’ve been baked to perfection. On Izu Oshima, there really is a gigantic rock formation affectionately known as the “Baumkuchen.” In this article, let’s uncover the story behind this incredible geological wonder and explore how nature spent thousands of years creating what looks like a giant slice of cake.
The Giant “Baumkuchen” of Izu Oshima
One of the places I was most excited to visit on my trip to Izu Oshima was this famous geological cross-section. Locals often call it the “Baumkuchen” because its alternating layers and golden-brown colors look astonishingly similar to the famous German cake.
At first glance, the wavy layers might make you think the rock has been bent and folded by powerful forces—a geological process known as folding. That was my first impression too.
Surprisingly, though, that’s not what happened here.
Instead, volcanic materials gradually piled up over an already uneven landscape. The hills and valleys that existed long before the eruptions simply became buried layer after layer, preserving the original contours beneath them. Rather than the ground being squeezed into shape, volcanic ash and scoria settled over the landscape much like snow covering mountains and valleys.
Over the past 18,000 years, more than 100 major eruptions deposited layer upon layer of volcanic material, gradually building the enormous striped pattern we see today. This spectacular outcrop wasn’t even discovered until 1953, when workers cut through the hillside to construct a road around the island. A chapter of Earth’s history that had been hidden underground for millennia was unexpectedly revealed through human engineering.
The Remarkable Black Layer That Tells the Story of an Island Being Born
Among all the layers, one especially thick black band of scoria immediately catches the eye. It’s the dark layer in the center of the photograph.
If you look beneath it, you’ll notice that the older layers are much more chaotic than those above.
Back then, Izu Oshima was still an underwater volcano. As the volcano was just beginning to emerge above the ocean’s surface, magma came into direct contact with seawater, triggering highly explosive eruptions. The material blasted out during those violent events formed this distinctive black, disturbed layer.
When seawater meets scorching magma, enormous amounts of steam are produced almost instantly, dramatically increasing the explosiveness of the eruption. Instead of settling into neat, even layers, the volcanic debris is scattered in every direction, leaving behind a much more chaotic deposit.
That single black layer records the extraordinary moment when Izu Oshima transformed from a submarine volcano into an island rising above the sea—a remarkable milestone preserved forever in stone.
How the “Baumkuchen” Was Built: A Three-Step Recipe
So how did these beautiful stripes form over thousands of years?
The basic cycle consists of three repeating steps.
1. A major eruption blankets the landscape with scoria and volcanic ash.
Powerful eruptions launch ash and fragments of volcanic rock high into the atmosphere. Carried by the wind, they eventually settle over the surrounding landscape, forming the dark-colored layers.
2. During quiet periods, the surface slowly weathers into soil.
Between eruptions, rain and wind gradually break down the surface. Fine dust carried by the wind accumulates over time, creating a thin layer of soil. These become the lighter-colored bands.
3. Another eruption covers everything once again.
Eventually the volcano erupts again, depositing a fresh blanket of ash and scoria on top of the soil.
This repeating sequence—a volcanic layer followed by a soil layer—is the basic building block of the cliff. Just as a baumkuchen cake is baked one thin ring at a time, the volcano added one geological “layer” after another over thousands of years.
When people think of rock layers, they often imagine sediments forming quietly on the seafloor. Seeing such perfectly preserved, dramatic layers created on land by volcanic activity was truly astonishing.
The thickness and color of each layer vary depending on the size of the eruption and how long the volcano remained quiet before erupting again. By carefully counting the layers, geologists can estimate how frequently the volcano erupted, much like counting the growth rings of a tree.
It’s amazing to think that a road construction project accidentally exposed nearly 18,000 years of volcanic history. Standing before this cliff, the stripes no longer look like ordinary rock layers—they feel more like the pages of a diary, recording the incredible story of how Izu Oshima came to be.
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