Pacaya
Pacaya has erupted continuously since 1963 with strombolian eruptions and lava flows. It is only 30 km south of the capital of Guatemala and easily reached by 4-wheel drive vehicle. Cars can approach but not as close. Unfortunately, this beautiful phenomenon must be visited with caution now, as thieves have systematically robbed robbed tourists recently. Check with knowledgeable travel or tour outfits before making a tourist visit here.
Pacaya's strombolian eruptions are often as closely spaced as every 5 minutes, although there is no strict periodicity. The magma is basalt, with low SiO2 (about 50%). The magma is not very viscous, so gases exsolve easily and grow into large bubbles that burst to make strombolian spatter. The primary characteristic of a strombolian eruption cloud is that its height is proportional to the initial velocity of the exploded fragments. There is no thermal convection because the thermal output is small, the particles are large and their low surface area to volume ratio makes them inefficient at transfering heat. The physics of cloud height is controlled by ballistic trajectories.
The lava flow picture shows how lavas grow walls or levees that constrain their flow. In the photo, a levee has just broken and a fragment of it is being rafted down the new channel. At the margins of the new channel, the lava is black, cooler and solidifying. It will freeze and grow higher as same lava spills over it, rapidly forming a new levee. Exposed lava freezes because its melting point, 1200C, is much higher than air. Thus, the margins of a flow always tend to stiffen up. At contact with air, a flow grows levees on both sides and a crust on top. The crust at the advancing front of the flow falls over the front edge and becomes the base as the liquid core of the flow overrides it. The crust is like a conveyer belt. It grows near the mouth, travels down between levees to the active front and is cascaded onto the ground in front of the flow. I try to sample near a flow mouth (boca) because the frozen crust there is the last material erupted, whereas the base of the levee, near the mouth, is the earliest erupted material.