The highly energetic geological processes inevitably accompanying the Genesis Flood must have generated an enormous heat load without raising environmental temperatures beyond biological endurance limits. This is the fourth in a series of papers intended to identify and, where possible, to quantify the key sources of Flood heat. Our primary concern in this paper is with the heat deposited as a result of Flood and post-Flood magmatic activity. Most of this heat must have been removed from earth's surface rocks and biosphere within at most a few hundred years. Related preliminary questions considered here include global energy totals, the relative importance of plumes and plates in mantle convection, the significance of two enormous mantle heterogeneities on the core-mantle boundary, the onset of plate tectonics, and the thermal history of the mantle. For future reference the relevant literature is briefly reviewed for each of these topics. The ocean floors represent by far the largest source of magmatic heat released during and since the Flood. Although this cooling problem was addressed by Worraker and Ward (2018), no solution compatible with a biblical timescale was found. Here possible ways of modifying and extending that work are considered, including variations in model input parameters and the proposal that rapid cooling might have been accomplished by 4D thermal radiation. Diffusion chronometry, an important technique for estimating the duration of geochemical processes, is considered in relation to cooling times, which are often found to be shorter than expected within the uniformitarian paradigm. Other field evidence of cooling modes and timescales is also considered. Large Igneous Provinces (LIPs) are next in importance. After describing their general characteristics, the heat deposited in the formation of LIPs is estimated; in terms of the thermal capacity of the oceans this is overwhelming. Although this heat is insignificant in comparison with ocean floor heat as a whole, potentially it could have produced drastic local effects. LIP eruption rates and eruption patterns are then discussed, followed by their emplacement and cooling modes, and the timescales involved. Diffusion chronometry again figures as important in estimating cooling times. Our main conclusion is that the heat deposited in the formation of the ocean floors and of LIPs is overwhelmingly large and cannot be removed by known natural processes within a biblically compatible timescale. We have noted, however, that this is only a problem for our limited understanding of the processes at work during the Flood, which very probably involved supernatural intervention: God was in full control of every aspect throughout. The literature on the thermal history of earth's mantle indicates a general cooling of approximately 150°C since the onset of the Flood; the range of mantle potential temperatures at any one stratigraphic level has been ~170°C throughout. However several potentially fruitful lines of further investigation are suggested.