Direct physical contact with magma is impossible due to the extreme temperatures involved. The intense heat would cause immediate, catastrophic harm long before any actual touch could occur. Understanding the sensory reality of this liquid rock requires exploring its physical properties, the overwhelming heat it radiates, and the varied textures it forms once it cools. The “feeling” of molten rock is therefore an indirect experience defined by thermal energy and resulting geological formations.
Magma vs. Lava: Defining the Difference
Magma is the term used for molten rock material, including dissolved gases and suspended crystals, when it remains beneath the Earth’s surface within underground chambers or conduits. The molten rock only becomes known as lava once it has been expelled from a volcanic vent or fissure and reaches the Earth’s surface. Any sensory experience involving liquid rock is inherently related to lava, not magma.
The Reality of Contact: Extreme Heat and Thermal Radiation
The primary sensation associated with active lava is not physical contact, but the overwhelming presence of intense heat. Erupting lava typically maintains temperatures ranging from approximately 700°C to over 1,200°C, depending on its chemical composition. This extreme heat source radiates thermal energy outward, making close proximity immediately dangerous. The danger is not primarily from the air heating up, but from the thermal radiation, which is an invisible form of energy transfer. This radiant heat flux travels through the air and is felt instantly, similar to standing very close to a massive bonfire, but multiplied many times over.
Objects and skin exposed to this radiative heat will rapidly combust or suffer severe burns. Even standing several meters away from a substantial lava flow, the heat can be so unbearable that it becomes physically difficult to breathe and forces a rapid retreat.
Viscosity and Flow: How Liquid Rock Moves
When lava is actively flowing, the closest indirect sensory experience is observing its movement, which is primarily dictated by its viscosity, or resistance to flow. This property is largely controlled by the lava’s silica content; lower silica results in runnier, less viscous lava, while high silica creates a thick, sticky material. Basaltic lavas, common in places like Hawaii, are low in silica and can flow relatively easily, sometimes compared to thick motor oil or slow-moving ketchup.
This runnier basaltic lava often forms two distinct types of flows, named with Hawaiian terms. Pahoehoe flows are characterized by a smooth, billowy, or ropy surface texture as the hot liquid beneath drags the quickly-cooled surface crust. A’a flows, conversely, form when the lava is slightly cooler or moves faster, causing the forming crust to break up into a jumbled mass of sharp, jagged blocks and clinkers.
Conversely, lavas rich in silica, such as rhyolite or dacite, are highly viscous, flowing more like thick, cold honey or even solid masses. This high internal friction means these lavas move extremely slowly, often piling up near the vent to form steep domes rather than flowing across the landscape.
The Solid State: Texture of Cooled Lava
The closest a person can come to physically “feeling” the material is by touching the resulting solid rock after it has cooled, which reveals a wide array of textures. The smooth, rope-like surface of cooled Pahoehoe can feel relatively gentle, though it is still abrasive and rough to the touch. In contrast, the surface of a cooled A’a flow is a chaotic field of sharp, broken blocks, requiring thick boots and gloves to traverse safely.
Rapid cooling can also create volcanic glass, such as obsidian, which has a remarkably smooth, conchoidal fracture but is also extremely sharp. When lava contains a high concentration of trapped gas bubbles, it forms highly porous rocks like scoria or pumice. Pumice, in particular, is so full of tiny air pockets that it can be incredibly lightweight, sometimes even floating on water, offering a surprisingly light and frothy texture for a rock.