The volcano Kilauea in Hawaii has been actively erupting for nearly a week out of several new fissures that have opened in a residential subdivision known as Leilani Estates. These events and the geology of the Hawaiian Islands have been summarized in a series of posts by @Sooflauschig that you might enjoy reading if you are interested in learning more.
While lava flows are common in Hawaii, the current activity is somewhat unique in that it is occurring in a populated area and has already destroyed dozens of houses. As the action is ongoing and new fissures are opening continually, I thought it would be pertinent to do a spatial analysis of the region in an attempt to assess the risk that these fissures might pose if they begin erupting significant amounts of lava. Based on the continued seismic activity in the area, it seems that the eruptions are not yet over. Let's see how the power of GIS can be utilized to help forecast this disaster.
In order to predict the direction of lava flow from the current fissures, we need be able to visualize the slope of Kilauea. There is elevation data available from the USGS, but the highest resolution Digital Elevation Model (DEM) is limited to 10 meters. Higher resolution data exists, but it is owned by a private company and is ridiculously expensive. For the purposes of this analysis, 10-meter resolution should suffice.
Upon obtaining the DEM, it was subjected to the slew of terrain calculations discussed in detail in my previous post Helping Communites 'Go Green'. With some light processing, the DEM was used to generate information on the slope, aspect, and terrain. Though lava is much more viscous than water, it still flows downhill in the same way (albeit much slower).
Leilani Estates is at the center of the current volcanic activity on Hawaii. The subdivision has hundreds of residents whose properties are at high risk of being overcome by lava flows and fire. The bulk of lava thus far has emerged from three fissures near the center of Leilani Estates and has moved over 1 kilometer downhill through the subdivision. Far to the west the red stars are locations where large cracks have developed in the road. The widening of these cracks suggest that fissures may develop here in the future. The fissures and cracks clearly follow a linear arcing trend running northwest / southeast, and they are all north of the dividing ridgeline created when this area experienced eruptions in 1955.
The area of activity is located on the eastern flank of Kilauea, approximately 40 kilometers from the summit crater. The highest point in this figure is in the bottom left (southwest) corner, causing a general sloping trend to the northeast. However, the ridge created by the 1955 eruptions (approximated by the dashed orange line) acts as a topographic division, with steep hills sloping toward the ocean to the south. Any eruptions north of this ridgeline will result in lava being directed northeast toward Leilani Estates.
As Hawaiian lava is exposed at the surface and loses heat, the viscosity gradually increases and the flow speed decreases. The steepness of the land has a profound influence on the rate at which any fluid material flows, especially as viscosity increases. In Leilani Estates, there are a few areas of moderate slope indicated by the northwest-trending yellow lines. Lava will tend to move downhill and perpendicular to these lines, but in flatter areas (shown in blue) the flow can spread laterally following the path of least resistance.
Coincident with the slope line analysis, aspect provides another way to quickly visualize the direction that the land is sloping. In this diagram, the majority of the fissures and nearly all of Leilani estates are colored in blue and green. This indicates that there is a general northeast slope downhill from the fissures. If the fissures had opened farther south on the other side of the ridge, the lava would flow south towards the ocean like it did in 1955.
There is an elegant analysis in the GrassGIS terraflow module known as a Topographic Convergence Index (TCI). A TCI is essentially a guide for how the terrain will influence water flowing on the surface. It examines the elevation, aspect, and slope to determine the topographic basins and is useful for predicting how lava will flow. In the above figure, areas of yellow and red are the lower drainages that will likely be the route followed by any future flows. The sections of Leilani Estates that are at highest risk of future lava flows depends on which fissures or cracks become active next. Based on the positions of the current openings, a series of flow risk zones can be established.
By synthesizing all of the information presented above and referencing the flows that have already occurred, it is possible to roughly predict where future lava flows might occur. For the residents whose houses are in the evacuation zone, they have a limited amount of time to return to their houses and retrieve items. This is not meant to be a comprehensive guide to what areas risk total destruction, but it is the best forecast that I can provide given the available data.
The forecasting of a moderate lava flow is based on the existing flow shown as an orange polygon. The distance that it traveled in relation to the slope and aspect that it flowed across was used to predict a similar flow from the other fissures and cracks. Moving from right to left,
Assuming that these eruptions continue for weeks or longer, there could be extreme amounts of lava flowing from the fissures. The above figure gives a forecast of what this scenario might look like. Moving from right to left,
It is important to understand that this is just an estimation of potential lava flow risk based on an analysis of elevation and the most recent spatial data. Every property on the eastern slope of Kilauea is at risk of being damaged or destroyed if things get worse, and it is impossible to predict exactly where new fissures might open in the future. The predicted lava flow paths that are included make several assumptions in regard to the volume of lava being extruded and the barriers that it may or may not encounter. The primary concerns are not limited to lava; fire, earthquakes, and toxic gases also poses a real threat.
For residents who live in a mandatory evacuation zone, it is advisable to remove your most important belongings while you still can and be prepared for the possibility of losing everything. A remotely sensed analysis of terrain using a 10-meter DEM can only go so far in accurately predicting what will happen. As lava flows and hardens, they create new barriers that may completely change the direction of subsequent flows. The only thing that seems to be certain at this point is that this disaster is far from over. I wish the best for all who have been directly or indirectly impacted by these events, and especially to those on the Island. Feel free to share this analysis with anyone who might find it useful or interesting!
